There both more factors involved, and more reasons for stiffer suspension. A major factor not discussed are the shocks. In the example above, the rate of wheel movement towards the ground (for the dip) did not factor in the shocks (rebound), nor did the bump example for the stiff spring. It is complicated. Beyond that, stiffer springs help prevent body roll/lean and help keep the tire flat to the ground. Soft springs allow the body to roll, which changes the effective camber of the tire. If you compensate by adding static negative camber, this sacrifices straight line braking... stiffer allows for less static camber. And, stiffer means generally less tire wear (which is a major factor in racing, either for cost or for stint length.) Finally, stiffer also is important for transitions from left turn to right (and vice-versa). Soft cars allow the body to roll from one side to the other and for that to be a large and slow transition. Stiff springs prevent the roll in the first place and switch to the other side faster. Stiffer tends to stabilize more quickly after sudden transitions. So, its quite complicated. There is no best. Generally, for smooth tracks, stiffer is better. Generally, for bumpy tracks, softer is better. (Those comments are to be taken relatively to each other.) Last but not least, driver preference/confidence vary a lot with how the car feels - some like stiffer/firmer (springs and shocks) and some like softer. So while the engineer may say one way or the other is technically or theoretically better, the driver may feel (and perform) better with a different setup. Thanks for considering a complicated and interesting topic.
"We have two cars driving. They're about to collide which is unfortunate..." This cracked me up. Probably because i am quite tired, but still, i thought it was funny that he found that worth mentioning. lol
I've always loved Colin Chapman's philosophy in car suspension design. Softer springs with long suspension travel always make for a better ride and better grip on rough roads. The main reason why mass production cars are given stiffer springs is because people have the tendency to rely on their perception that cars that roll are more likely to lose grip on a fast turn.
Cars that roll don’t handle as well, it’s a simple fact..also we don’t drive at freeway speeds in cars off road, he seems to forget suspension settings are able the road surface your driving on,which dictates the suspension settings which work best..off road a softer longer setting is best , on a road course it’s a different beast, and even then having a adjustable setup is best
Soft if you can handle the roll, since a soft suspension means grip. I've noticed that in some cars, just upgrading anti-roll bars and adding sticky tires improves the handling a much greater amount than when a lowered and stiffer suspension was added.
Unbearable Pain I disagree. Some people say the primary roll stiffness should come from the springs, not the sway bars. The sway bars reduce the independence of the suspension.
TassieLorenzo totally untrue... wheel indepenence ist not nessesarily a good thing. the myth that stiff suspension and hard dampers are a good thing comes from formula 1. in formula 1 you want the car to have the same attitude to the road at all times to maximize downforce. "mechanical grip" is irrelevant in F1. but since a roadcar has no downforce soft suspension will be better. thats also the reason why for example ralleycars have really soft suspension compared to for example f1 cars even when the are driving a tarmac ralley.
MrBusunglueck "but since a roadcar has no downforce soft suspension will be better. " Then why do road-based race cars with no downforce have stiff suspension? ;)... I agree there is such a thing as too stiff, but driving some road car on a track day with Hoosiers and using stock comfort-tuned suspension will give a terrifying wallowy feeling and feeling of lack of control. There is a REASON after all why PROPER sporty cars like Renault Megane RS, Civic Type R, Lancer Evolution, indeed Ferrari F430, etc all come with relatively stiff suspension.... surely? ;)
TassieLorenzo the thing is... racecars with no downforce dont have stiff suspension. the reason why all sportscars are stiff is cause thats what people want. the nurburgring laptime off the current 911 turbo s for example was set with the dampers in comfort mode. the nurburgring is a bumpy track, but still that says a lot for me.
2 more reasons why stiff springs work well on the track: 1. To give a driver better feedback with regard to surface changes or communicate tire compliance with the road. So if you hit a spot of gravel vs ice you can feel the changes. 2. Also with higher speeds on a track, impacts from road surface changes or even suspension movement due to braking or cornering causes more travel and uses suspension compliance forcing the shock to operate outside of it's optimum stroke. So stiffer suspension is needed in order for the components to handle higher speeds. Granted your tires still have to be good enough to generate the traction needed to allow for it's proper operation or you can loose more traction because of the loss of compliance.
I am a bit confused. If we are just looking at spring rate, why aren't we looking at a spring that has enough travel to reach the 20mm? In that case the stiff spring would win, the only reason it loses is because it runs out of travel and gravity has to do the rest as you mentioned. I guess the video is not about preloading the spring and the only source of compression is vehicle weight. If it was preloaded (as almost all passenger cars are, and why spring removal has to be done carefully even when the wheels are lifted off the ground), then the stiff spring should have ~10X faster ground contact in the dip. Your point is very valid on the bump force though.
davetek490 The amount the spring compresses is based on the weight on it. A stiffer spring will compress less, and thus have less travel. 10x faster ground contact? Nope, the math says otherwise (even in the portion where there is still travel remaining).
Engineering Explained For the sake of being devils advocate I'm assuming a preload to allow stiff spring to travel 20mm. The stiffer spring has higher F/mm.... if F=ma, then if both springs are allowed to travel the full 20mm, at every mm of travel, the stiffer spring has more force. if a=F/m and m is constant, a is linearly higher with respect to F. I must be missing something.
davetek490 The thing you're missing is that as the spring releases (look at the graph I drew) the amount of force it presses decreases (rapidly with a stiff spring, slowly with a soft spring). The maximum force both springs press is the same, but the soft spring will press with a greater force for longer (it does more work).
Engineering Explained Ok, and that's only true in the case where the only force used to preload the spring is the 1000kg car. I get you, I think we're just using different initial conditions. Thanks for the explanation.
davetek490 a soft spring will make the car bouncy when the mass of the car is moving, like when you go over a crest. to stop this you ned a shockobsorber to steady out the pressure on tyres to keap traction. does a soft spring not need a harder obsorber with gives a harder spring some advatage when it comes to travel? great explanation on springs, very intresting
Every time I watch your videos like this one, you just make me want to keep my car stock, and just learn how to drive what I have better. So thanks for saving me money lol.
When you add the effects of compression and rebound dampening (oil damper), this gets much more complicated than just a spring with no damper. In fact, a spring alone does a terrible job of keeping the wheel on the ground. Playing with dirt bike suspension in the good old days of Motocross (using about 12" of travel), I found I actually got a plusher ride with a stiffer spring (front forks, and very little preload on the springs), that still resisted big bumps with less compression dampening, and more rebound dampening (assuming the dampers were set correctly with the stock springs). As for the preloaded travel of a dirt bike, you pretty much want your suspension to have eaten up about 33% of the total travel with you on the bike, no matter what your spring rates are, and that is adjusted by a preload ring that compresses the spring. But, if you add the dampening,--I bet the math work goes up exponentially---but it still has to work as well in the real world, and will need field testing to fix. Sophisticated suspension, (depending on the demands and severity of the application), seems to be one of those things that almost never comes off the drawing table very well. You should look at some of the front forks of MX bikes today. Nobody knows how to adjust them, there are so many knobs and air chambers. But one fork on Yamaha the kabaya (sp) SSS forks, that is over 10 yer old technology, and still uses a spring, romps them all in overall performance and probably every category. You post great stuff young man. I hope there are more like you.
If he wanted to bottom up design a car, I would help fund the dude. Guy should start a kickstarter collaborative with other car guys and design and build an affordable sports car that can be mass produced.
Why? He's just doing the same kind of engineering that's made at the factory. The output in that case would be a really nice, well engineered premium car, nothing out of this world.
4 those of u who didn't fully understand. What he has explained is the perfect formula to base a suspension set up "coilovers". Thanks to this man and his video I understand completely on how to set up my car the way I want it. There are an infinite amount of spring rate set ups. What it comes down too is your own style of driving to formulate a functional set up for both street and track "AutoX". I'm headed in that direction. I want the best of both worlds because math makes that possible. Thank you for your injenuity.
There is a very important point you missed, if not the most important. Roadcars are optimized for straight line rolling where load is equally dstributed to both sides of the car. Racecars are optimized for cornering where load is shifted to the outside wheels. So you need to calcualte spring stiffness and damping rate to that amount of load. when you corner with a soft spring, you lose alot of suspension travel right at the start because of body roll, thats because the springs are too soft for that scenario. with a stiffer spring you optimize for higher load, giving you less body roll and more suspension travel remains available mid corner. higher damping rates need to follow the higher spring rates in order to prevent unvanted body oscillating movement.
great video as usual but you gotta also count/add that stiffer setup enables car to react faster to driver inputs, especially during direction changes (which is what racing is about)
I'm surprised people actually still debated this. This was spot on to what I learned in school. stiffer suspension for street driven cars isn't always better. example: I had a 7gen galant that I threw springs (1in front/rear) and adjustable shocks on. Hard cornering was great, but the overall quality wasn't great, especially in the rain. I went through alot of trial and errors before I figured out that soft is safe.
There're 3 basic things who affect each other: Range of spring, spring rate and the shock absorber. Particularly the shock absorbers have to be well matched. For example there are high- and low-speed compression/rebound-stages and also the viscosity of the damping oil matters.
I used to race superbikes and the suspension settings always had me on the fly, it depends on temperature and surface conditions you will use, for normal street use you can set a medium setting it will get the best of both sides from soft to hard, it is quite tricky to find the right setting at the beginning, but you will get use to it.
Roll is grip, if you can control it. Can't remember where I heard that the first time, but it's catchy and quickly explains the effects of spring rate.
Jason, first off, a big fan thank you for making these videos for all of us to better understand the engineering behind cars and suspensions, they have been a big help for me in understanding what parts I might invest into my ride. I wanted to ask a clarifying question about the video, which is in reference to the drop that the wheel would have into the hypothetical pothole you discussed in this video. I understand what you were trying to say in the aspect of the importance of keeping all 4 tires on the ground as much as possible and with as much force as possible as this is the point of a suspension. However, what I am struggling with is understanding how the stiffer spring, that only compresses 10mm, would have a harder time hitting the ground compared to the softer spring that compresses 80mm. I struggle with envisioning this as being something that follows other aspects of physics, such as the overall weight of the car, and the speed as to which the wheel hits the bottom of the hypothetical pothole. If the stiffer spring only compresses 10mm and the pothole is deeper than 10mm then that would leave the assumption that the spring does not decompress further than 10mm, which when a car is lifted there is full droop in all 4 wheels, which is in response to the shocks and springs being fully extended and not being under pressure. For what you were saying in the video that the stiffer springs would not either reach the bottom of the pothole in the time that the softer ones would reach would also be assuming that the shocks are not factored into this statement because if what you were saying was the case then a car’s wheel would never experience full droop and would return to the base ride height + the decompression of the spring (10mm). I am confused because the speed as to when that wheel would hit the bottom of the pothole would also be dependent on the speed of the car moving forward + the speed of gravity as the car is being pulled down to the bottom of the pothole. It would sort of question also the speed difference between the spring decompressing and the speed of gravity (both forces would be happening simultaneously, the car falling and the spring decompressing). It also brings into question the force that would be impacted on the fall as well and looking at the spring rate to determine if the car’s force from the fall and momentum would cause the spring to compress more, thus potentially leading to bottoming out. As I see it, and I could be wrong, we have 3 forces in this hypothetical situation (the shocks, springs and gravity) and in “forces” I mean all things that would cause the wheel of the car to move downward in the event of driving over a pothole. All 3 would need to be taken into consideration when discussing the cons to stiffer springs, correct?
Very good explanation ! As you know & have to keep it simple for the layman . Shock absorbers , sway bars , bushings & tires etc. are also components of a suspension system & on the track , settings are softer in the wet vs. racing in dry conditions . Thanks for helping alot of people by posting this video !
For some that may not know the numbers used are specifically to show his point and are quite exaggerated compared real life. For ex he uses 1000kg of force but my entire car only weighs about 1200kg and you would never change your suspension by a factor of 10. Great explanation and the number make the calculations clean and easy to understand which I applaud just want the audience to know changing your suspension isn't going to wreck your car going up/down a 10mm gap.
One thing he didn't address is that softer springs will allow the unsprung weight of the wheel to induce further suspension compression which can cause the tire to lose contact with the road for a longer period of time as it goes through the compression and rebound cycle. A badly washboarded road is a good example. If your soft springs allow the wheel a greater range of motion and a slower rebound, you will have less braking and turning traction with that wheel. If you hit a series of consecutive bumps the tire can bounce up and down on the road like a basketball. No tire has grip when it is in the air. You can compensate with stiffer shocks, but the shock and springs should be changed simultaneously or either can wear out prematurely. This is why it's a bad idea to add lower (shorter) springs while keeping the same shocks. They must have similar driving and handling characteristics and capabilities.
+Chris Ashcroft This is not correct. On a washboarded road the tire will maintain contact much more with a softer spring than with a stiffer spring, which will bounce the whole car. The reason this is true is demonstrated mathematically in the video, as the force pressing down on the spring will remain greater for whatever amount of travel there is in the spring. Think about a car with no suspension (aka, infinitely stiff springs). In this case, as you hit any bump, the entire car is forced up (and the tire loses contact). If the spring is super soft, the suspension travel will absorb the bump, and the tire will maintain contact with the road.
+Engineering Explained For a very stiff spring, yes, but what about a very soft spring? Now the spring is under control of the dampening (compression and rebound dampening), to help the tire follow the road. But, for a hypothetical example, if the spring rate is soft (or not hard enough to rebound quickly), over stutter bumps, the shock could actually "pack" up into it's travel, because the next bump and next bump and the next bump compressed the shock more, and more, and more, until the spring rate is in a stiffer range of motion or the suspension bottoms out. When that happens, it could act a lot like a overly stiff spring, forcing the chassis upwards. Selecting the correct spring rate for your application is probably more important than getting the dampening dialed in, but they have to work together, and it is usually futile to try to tinker with dampening if you have the wrong spring rate. I learned something during the dirt bike suspension evolution from about 3" of travel to about 12" of travel. It was not always the longer travel that made a suspension perform better, but how well the spring and dampening handle the travel you have.
+Chris Ashcroft not only am I an engineer but I drive washboarded unsealed roads every day. I have two identical cars (GC Mazda 626s). One is turbocharged and my toy on the track with correspondingly stiff suspension. It is a nightmare to drive on these roads. My carburetted daily driver has very soft suspension with a high spring rate and glides over these surface imperfections with ease. When cornering on these surfaces it is much more stable than the track designed one.
the rx-8 has a much softer suspension then the fd 7 for exactly that reason. it's almost unbelievable how well it mantains grip. damn fast in the real world, but not so much on a race track. that's one of the main reasons why i didn't buy an s2000. there also is the benefit of a smoother ride.
WRC cars have softer springs on tricky gravel tracks ans stiff spring on tarmac mostly. i agree with this guy. there's a lot of accidents with cats super 7 and lotus elise on mountain tracks due to the very stiff suspension configuration, its so stiff and short that the wheel cant fill the whole gap during a depression. result, lack of traction. mountain roads work better with medium spring rates, gravel with soft and corsa with stiff. it all depends of the amplitude of the irregularities. short amplitude, stiff, long amplitude soft.
springs....coils of metal...thats it..... I gotta say, the half course of physics I took, the most amazing thing to me was how refined the concept of a spring is. So simple and so useful. I just love this stuff. Great video! I wish I knew more. Guess I gotta go take a full physics course next....Thanks brother!
+TheRealDannyE The lower the offset number, the more the wheel will stick out. the higher the offset the wheel will be more in the wheel well and will be less aggressive. every car uses different offsets. So you have to choose wisely
Further to the discussion, dedicated off-road vehicles typically use very soft suspensions to ensure transverse tire contact. A typical issue with hard suspensions off-road (read: Stock Pickup Trucks) is that the relatively low spring rate means that traversing a large bump with one wheel on a beam-axle suspension causes the other wheel to lift, thus reducing ground contact and traction. Essentially, instead of absorbing the bump into the suspensions travel, that bump causes the body to lift, which then because of the low spring rate, reduces the effective down-pressure on the other wheel on that axle. A loss of downwards pressure is a loss of traction. It's for this reason that dedicated off-road vehicles like Land Rovers and Jeeps typically use very soft suspensions (or variable spring rate suspensions like air-springs) to ensure that traversing a bump does not cause a total loss of traction for the vehicle. Pickup trucks on the other hand typically use multiple leaf springs with a very low spring rate because they're primarily designed to carry great deals of weight in the pickup bed. A stiff rear spring on a pickup truck is a decided advantage when carrying load, but a decided disadvantage when used off-road. If you're serious about off-roading a pickup truck, replacing the stock springs with much softer leafs and adding a levelling air-bag can make a huge difference to off-road performance.
I would love to see some sponsored content from Ohlins suspension on this channel. They are supposedly some of the most beautifully and meticulously designed suspension in terms of the quality of engineering and RnD that goes in to them. Plus they make them for your S2000 so you could get a set and try it out for free probably. I am interested to know how much of a difference their Dual Flow Valve technology makes on the street
I think a stiffer spring is better if tyres keeps contact to the ground, so after this point going soft will only decrease grip as it changes alignment unnecessarily like camber and toe.
I usually enjoy your videos but this one has some bad logic. This is a very very special case, which almost never occurs. That is hitting a bump larger than your suspension droop. I've had cars on 12kg and 10kg springs. Even an FC RX7 with Mcpherson front suspension of almost 1:1 moment arm with 12kg springs would have nearly an inch of droop. Don't know about you but if there's a road with that crazy of a drop, I'm not driving on it! So following that special case you're discounting all the other benefits of stiff springs and claiming that softer springs are better for the street?
TheXdmgx7 The logic is sound. Softer springs will allow for more compliance with the road (even if the examples are exaggerated to keep the math simple and explain a point). This doesn't mean soft is "best" for the street, it's simply factual that in non-perfect conditions it will do a better job of maintaining contact with the ground. Design for what road conditions you intend to drive on.
TheXdmgx7 It becomes a problem when you consider the force on the body creating an upward acceleration from stiff springs. The back side of a 10mm bump can cause an aftermarket suspension to lose contact with the ground because the body continues it's velocity upward which drags the wheels up with it an reduces the load on the springs, which removes droop velocity. Using an aftermarket ride height and spring perch separated adjustment coilover you can easily tune the suspension to be harsh either on the front side or back side of bumps using the preload adjustment on the lower spring perch. If you have conventional single collar adjustable coilovers this won't work because you cannot preload. For instance, i can set up my coilovers to have zero preload and thus maximum shock compression at static height, which will make it more likely for the shock to contact the bump stops, drastically increasing effective spring rate over sufficiently sized bumps and causing compression to be uncomfortable. In reverse, I can preload the spring to the point of zero shock compression at static height and as such giving the shock minimum droop travel, making the front side impact of bumps very gooshy but the back side of bumps like falling off a cliff. So it depends on the ratio of shock length and spring rate to determine the actual road-contacty-ness of a coilover.
Engineering Explained I agree that in non-ideal(horrible) conditions softer springs will do a better job maintaining traction but you did not claim that softer springs are better for non-ideal conditions. You claimed softer springs are better because the harder spring will run out of droop if you jump a huge curb and you will lose contact. In the real world it is VERY hard to lose contact due to inadequate suspension droop. (I'd be dead 10 times over if that wasn't the case)
TheXdmgx7 your assertions about the difficulty of losing contact depend entirely on the properties of the shock and spring combination. My coilovers can and do regularly lose contact with the ground. Engineering's extreme examples lay the groundwork for how relative wheel and chassis velocities work together. He is correct. You're just having trouble working between the extremes. In his example, wheel forces of 2g, 4g, 6g etc between the two extremes of 1g and 10g are possible. Those forces relate to how quickly the wheel follows the back side of every bump. The closer to 1g the more often the car will lose contact with the road. This can be due to spring rate, damper settings (over-damping on rebound for instance, lowering wheel velocity on extension) and of course limited droop travel (which is the problem with my coilovers).
Gregory Evans I completely agree, yet this is not enough of a reason for the claim "softer springs are better for the street." My problem is not with the overly simplified math but with stretching it and using it as a proof for a much more broad claim. An example would be the moose test(Real world, right?)... How do you think a softly sprung car will do? It'll be less responsive due to the delayed weight transfer. See my point?
Ok you helped us scratch the surface of understanding basic suspension physics. I think it would be great to talk about suspension setup on race cars both on road and off road that would be a very helpful video
All of your reasoning was pretty sound and the science was definitely correct. The only thing that struck me as a bit odd was that the comparison was pretty unrealistic. Nobody ever puts a spring that's 10x higher in spring rate while using the car for the same application ie. street driving etc. Typically, I see most tuners and companies going to a 1.5-4x spring rates depending on how stiff the car initially was and/or how much suspension travel they intend to utilize. That might have made a more reasonable comparison. Great video, nonetheless.
Ok, the thing is that stiff springs are supposed to be used on tracks, because they affect weight distribution and weight shift and also handling, stiffer springs allow more weight to be charged on them without the worry of them being squeezed to death so this allows them to handle drift better allowing you to go faster, on the other hand soft springs really shines in everything else because either on track (only of you are a grip guy) or a downhill/uphill scenario you have overall better grip as well as a smooth turn, but at contrary if you want to drift you will have to go slower to avoid hitting the wall and it's easier to spin out so, on a soft spring drive grippy and safe, please correct me if i'm wrong, always looking forward to improve :)
***** Rally drivers also slide their cars because of a technique called "late apex turning" it just allows the driver to see more of turn before having to decide if he/she needs to turn a lot or little. The body roll sounds like a good point as well for why they slide though too
lowering its not the only way to reduce body roll. anti-sway bars at the front and rear, tuned for your car, will reduce body roll maintaining the under/oversteer balance. a lot of cars of today have soft dampers with stiff sway bars.
I enjoyed the concepts provided by this video. I race as a hobby and have used stock soft to quite firm suspension setups both on and off road. I do think you need to discuss mass and damper reactions to these forces in order to fully understand the resulting motion as you experience them in the car. I think it's a little too simplified just to talk about a spring alone. Cars are dynamic systems. Even during steady state cornering, cars are still moving about, increasing, and decreasing applied force to the tires. For sport driving, stiffer is good in that it reacts faster. There's less time between input, settling of the chassis, and reactions. In many cases, reaction speed is a big factor in going fast. If a car is too sluggish, you might have a hard time transitioning through very dynamic sections without first slowing down a little in order to buy time for the car to react. The stiffness also can help generate tire loading forces specifically due to its ability to ramp up force via a jab of the brakes or flick of the steering wheel. Granted, the damper is playing a big roll in this while spring rates play second fiddle. Still, stiffness equals dynamic speed.
Very nice explanation why race cars have stiff suspension, but what about off road vehicles. They too have stiffer springs, and their track is by no means smooth. Thanks and keep up the good work!!
When racing downhill mountain bikes I tend to set my suspension up to be using about 75% travel to float over most terrain. If it is not using that much, i soften the spring rate and/or back of compression damping. The last 25% is used for g-out situations durning landings and such. Using this much suspension travel makes for an active and smooth ride.....any less and you are suffering unnecessarily and could be going faster. The only problem is that a huge compression coupled with an impact like a stone can blow into the bumpstop and dig deeply into the tire thickness often causing a pinch flat. it creates a condition where there is a huge risk of flatting but the massive amount of control will (hopefully) allow me to avoid those obstacles. Tire pressure is hugely important as it changes the frequency of the small chatter type bumps and works thoroughly in conjunction with the suspension. Tire technology has improved so much in cars and bikes that it is easier to avoid flats. This balance between compression and rebound damping, tire pressure, spring rate and rising/falling rate suspension can not be figured out mathematically and there is always a compromise. I tend to go soft and avoid big hits....I'm light and so are my vehicles. Big guys/heavy vehicles have to beef things up more and the weight begins to push heavier into the tires. I might run 30 psi where big guys will run 45-60. They handle the big hits but bounce around on the little stuff. For cars and street, set it up for where you want performance. Straight lines, or on ramps? Choppy alleys or highways? I like to be able to blow through transitions, chop and chatter with minimal fuss, smash speed bumps and humps and drive like a crazed rally driver. I'd prefer to not slow down over every rise or parking transition. I want to be able to keep up with most people on smooth but not necessary beat them in my 2800 lb truck and say bye bye over the crappy sections. I seem to get around better than most road cars and our town has terrible roads. Temperature also affects the durameter of the tires. Tuning the tire pressure is equally important to spring rate. If I were upgrading a car, I'd start with firmer/lower profile tires and then moderate spring stiffening after. If your vehicle is fairly good as it is, adjust incrementally.
+GunFun ZS Used those on an old caprice. Car was smooth sailing, but when it came time to load up, and you can load those things, didn't have to worry about sagging or bottoming out on a big bump.
I didn't get all of the verbal jargon a but I understood what you're saying as I feel them out on the road and track having stiff spring rates on both my cars.
Seems like you just talked about compression and left out preload and rebound. Your videos are great but to explain the real reasons behind race/street suspension in 6 minutes is impossible.
Hi very interesting.....I could suggest that what you said about the springs in a suspension system applies also to the profile of tyres. The higher the profile the more comfortable ride. Remember road races and your skinny tyres
Since I did spend a bit of my career as a suspension engineer - for the sake of the viewers - I would like to here more about ride quality at speed and the compromise of ride vs turning handling.
That may be right on some cars. 1. Variable grip level of tire through body roll ads force to the tires. Remember you are balancing thousands of pounds on 4 small patches. If your spring has too much play the car will only shift the the side that G forces are acting on. Meaning understeer or oversteer Sports cars have the set up and power to hold more G forces on a constant road surface.
TassieLorenzo Also means he can enter a corner faster, go look up suspension dynamics and you will see what going with a soft front vs a hard front does. Also oversteer is better than understeer as it can be controlled with enough practice.
TassieLorenzo oversteer is better than understeer and like they are right, soft front gives you better grip on the front wheels so better conering speed
Really good video and good food for thought. The only thing I would add to this, is particular with regards to racecars as a rough rule of thumb the stiffer the suspension, both in spring and bar the more it will put temperature into the tyre. Consequently when you start running race rubber you always play a delicate balancing act between mechanical grip and ensuring the tyre is up to temp.
+Adnan Rahman I believe spring rate is about the force necessary to generate each 1mm of compression in the spring. so, the higher the spring rate, the stiffer the spring is.
Adnan Rahman haha i get what you mean. i think what throws people off is that the word "rate" is often used by normal people to describe some sort of speed or change in distance over time. here, it's really more about the spring's compression, so not much to do with time at all. glad it helped you!
As usual, this is a great video on a great subject. However, I'm seeing a lot of confusion on this topic, so I thought I'd try to help those trying to learn with a little more "real world" application of these concepts that were likely beyond the scope of this video. Suspension set-up (and the related subject of vehicle dynamics) is a VERY complex subject. You cannot just make blanket statements like "stiff is better, bro" or "soft is faster, dude." Suspension tuning is not a binary decision between either extremely stiff or completely soft. Those arguing for either/or are missing the point. All race car set-ups are a trade-off between COMPLIANCE and vehicle RESPONSE to driver's inputs, and that applies to everything: dampers, roll bars and springs.. The more you stiffen the car, the more total vehicle grip and traction you actually lose, but you gain improved response to vehicle direction change. You have to find the cross-over point. Too much roll and the car feels sloppy and slow to change direction. Too stiff and the vehicle will be very responsive in change of direction but you’re actually losing grip, and combined with a lack of compliance ,it will make the car slide all over the place, chatter over the bumps,etc. which does nothing but destroy the tires which just compounds the handling problems. The "correct" set-up will always depend on track characteristics and driver preference, and in the case of street car performance set-ups, a compromise between all of this and vehicle ride characteristics. I'm sure everyone has ridden in the tuned car on the street with a suspension so overly stiff it crashes over the smallest bumps and rattles the fillings out of your back teeth. I highly advise anyone out there wanting to learn more about this subject to read the great books on this subject like Tune to Win by Carroll Smith and How to Make Your Car Handle by Fred Puhn. You will learn a lot for the investment in time.
What if the driver is 70 kg or 130Kg :D if u have soft springs and the person is heavy... than you get hard springs I think it is personal what the driver like, Comfortable or sport drive
yes maybe when the car is 1500kg then u not can see it maybe, but when i see my friend from 100kg step in his lowering car 980kg.. i see the car go more down on his side
MMD While the vast majority of cars are nowhere near that small, a 60 kg difference is still only 6% of the car. The car's stock suspension is designed to work with that kind of load and does not require a stiffer suspension.
Better is subjective based on the goal of the user. Suspension is not only to help maintain contact with the ground, but to affect how quickly or slowly the vehicle turns (provided the tires have stiff sidewalls) and the comfort of the passengers.
As has been stated, in the racing world, you go with as soft a spring as possible. If a car has downforce, and is very pitch-sensitive because of said downforce, you will end up being forced to run a stiffer spring. Many of the new GT cars have front splitters designed to create massive downforce when placed close to the ground. Not only are they very pitch-sensitive, but they have to be withing a couple inches of the racing surface. Obviously with such limited ride height and pitch allowance, very stiff springs are used. For people bringing up spring splits, this is how one would balance the car. Usually, race cars will tend to like a certain spring split "window", a specific F/R spring ratio that moves together when stiffening/softening the car. This ratio can be moved slightly to affect the balance of the car in different parts of the corner. Also understand that a "big spring" will take a "big damper" to control it. This is very complex process, so please don't say things like "you can usually go with X front and Y rear". Without knowing car weight, motion ratio of the wheel, intended ride height, intended use, tire type, etc., you really can't state a spring rate.
Very good video, thanks. I may add few things. Lets look at stiff suspension pros & cons and we may assume the soft susp. will be reverse of these. stiff susp. pros: as you expressed on your video plus, stiff suspensions allow more precise handling on smooth surfaces and they tend to more responsive to driver inputs than the softer suspension. cons * relatively quick tire wear * difficult handling on bumpy surfaces and more stress on suspension members & attached points. * not comfortable IMHO the best suspension is.. what is the definition of the "best" btw? Ok, let's say average "best" for the sake of the argument, it is dependent to the surface quality, road conditions, appropriateness of tires, the driver and maybe the mood of the driver :)
I think both work. But for a stiff one you need a resistant car (frame, body, and every articulation) because the suspension is not soft enough to absorb shock so it is transmitted to the whole car. For soft ones, the only problem are body roll, wave, lean. The car (frame etc.) is more protected cause the movements will be smothier. The soft sprint can absorb the movements as they can shape faster. Shock absorbers will not help much because if you use strong ones, it will limit the advantage you get from soft springs. The ideal would be soft spring+variable shock absorbers able to variably absorb shocks. For example, letting the tire goes down (smoof spring) but harden and do not allow the car to be wavy once the bump is done.
to build on earlier comments, I would like to see a follow-on of this video not just showing the extremes of very tall soft springs vs very short stiff springs, but realistic middle ground and typical suspension swaps.
Stiffer springs help maintaining lower diving on heavy braking and turning. This is helpful because the sudden changes of load disrupt the balance of the vehicle and the contact patch of the tires. Having said that, most of the times racing cars' suspensions (that applies to bikes also) have stiffer rebound settings which actually help keeping the tires on the ground more under heavy acceleration or braking. That's why most of the times when tuning a car you don't mess with the springs instead you change the shocks. Just my 2 cents...
thanks for this video!!! very structured and well made! one minor thing i want to add, you said beginning at 3:45 that "the softer spring presses it [the wheel] down faster". In your example both springs press the wheels down equally fast, the stiffer spring is just less mm compressed in your case. your sentence implied (my opinion) that the softer spring itself is faster. you made it very clear that the rest of the travel distance to the ground is pulled by earth graviation, but this sentence alone seems a bit missleading for me. is this nitpicking? i hope you dont get mad over me! i really like your videos, please continue!! ;) cheers!
Phil Langer What I'm implying is that the wheel with a soft spring with more travel will contact the ground faster than the stiff spring with less travel. Less travel is a result of the stiffness of the spring, so they've very much intertwined.
Engineering Explained in your example yes the softer tyre with more travel would act faster but if the bump was smaller, like a race track bump of 10mm or less then the stiffer spring would react quicker, which is why race cars have those short suspension travel stiff spring setups. Also a softer spring is more compliant, easier to put power down etc however slower to react to weight shift. Understand though there are so so many aspects you can't cover it in one video. Suspension and spring setups are a fine art..
BenjiMC1 I would agree with Jason in the softer spring get's to the ground faster, even in your 10mm example. What you are neglecting is the pre-load on the springs. Both springs are pre-loaded with 10,000N but if the stiff spring experiences a 1 mm dip in the road it now only has 9000N while the soft spring (all from his example) would have 9900N. Since a=F/m the soft spring has more force with the same mass thus higher acceleration towards the new surface in the road.
In general softer suspension are better suitable for road cars which constant meets unexpected and uneven road surfaces. Race cars on race track which constantly drive at very high speed on controled flat surfaces should use hard suspension setup. Because of aerodynamic lifts and down forces effects the racer so you must use hard suspension setup to maintain the height. Some people still don't have any clue due to the amount of softness and hardness to use for customize their own vehicle. Although not all the time but most of the time your vehicle manufacturer's engineers has calculated the best compomise settings for your vehicle's main use purpose. But randomly some owners may not agrees with his OEM setup. So if you need to customize it then you must figure out how much softer or harder than the OEM. Not surprisingly it will be trials and errors for your perfect setting. Unless you have the opportunity to full access to your manufacture's engineering faculty or luckly for you the after market supplying you an exact test mule as your vehicle. If you still don't understand why and how, then stick with OEM can't go wrong. After all you are betting with your wallet.😇
When the car is driving at high speed, the frequency of the bump accelerates, and if the tire is to get maximum grip, the shock-absorbing system that requires a short travel schedule can follow the frequency of the bump.
Wow! I had never heard that before! I thought the purpose of the suspension was to keep the vibrations of the road from loosening bolts and ripping parts off the car! So, you're saying that the suspension is designed to keep the car tethered to the ground! Well, I guess you learn something every day!! ( I have a go-kart with no suspension, and I am constantly having to tighten the bolts and mounts after I drive it offroad. I just assumed...)
This is why the Alfasud was the best handling ROAD car in its time. Public roads are not flat and hole free, so soft long travel with good damping is the way to go. There is a reason why WRC cars have such huge suspension travel compared to an F1 car. Body roll is not a problem with a properly designed multi link suspension, where toe and camber are controlled. The choice of dampers is more important, getting the balance of bump and rebound matched to the spring rates and body mass.
I like Carrol Smith's advice.. Have just enough spring to keep the nose off the pavement under maximum braking load. Do the rest with sway bars. Also feels like relatively softer in bump and stiffer in rebound for the shocks seems like a good idea.
ive tried stiff/soft suspension on a corolla for street driving and honestly the only difference i can feel is the stiffness and softness of the springs. i can push the same speed around ramps and canyon curves and the tires will stick to the ground. the difference between the two for me is the feel of the car. in my case, i would leave my car with softer springs bc its convenient and does what i want/need it to do opposed using stiffer springs.
+Bee Vang I felt the same with my old corona, I felt I had more control with the softer springs on canyon/mountain roads, stiffer and the car loved to understeer. Plus stiff springs on the street I felt would wear out my chassis.
There is another factor in play - damper rate. A stiffer spring demands a tighter damper to control it at resonance. Damper rates are measured in m*sec^-1*N^-1. Tighter dampers transfer more shocks. Yet another factor is the lowpass filter created by the spring and the mass. The tighter the spring the higher the frequency at which the filter operates. In other words the stiffer spring transfers vibration at a higher frequency into the car body, resulting in excess road noise and passenger discomfort.
The springs should be as soft as possible, but as hard as necessary. While the stock suspension of a Integra GSi is perfectly adequate for circa 1995 all-season tyres (as fitted and engineered for when it was new), when you throw on Hoosier R-compounds, probably on a 8-inch wide rim instead of the stock 6.5-inch wide rim, and take it to an autocross suddenly it's no longer as "hard as necessary"... Hence uprated springs/shocks or coilovers being required. :)
Ideally every motion, (ride, pitch, roll) of a vehicle should be controlled by a separate set of spring and dampers. I think it is more appropriate to say this video covers more about ride spring which control the vertical motion of the car. In general ride spring is set as soft as you can get away with that provides enough support so the car don't bottom out and don't over extend given the type of surface the car will have to negotiate. However most vehicle we see on the road are not designed with ride spring that only controls ride, but also pitch and roll. This results in a compromising situation where you can't go as soft as you want on ride while maintain high pitch and roll response like you want in a racing situation.
It depends on if you're driving on or off-road along with personal driving preference. I drive on pavement and my car has a low center of gravity, wallowing like a pig doesn't do anything good for steering compliance - so stiff is the way I prefer it. It's more manueverable and responsive. If I liked driving trucks I'd probably have a different opinion. Of course these days many cars are made with variable-rate springs. An attempt to split the difference for the best of both worlds.
Herb Adams (has a book, chassis engineering) said IIRC, soft springs, stiff shocks, big sway bars and used big jounce bumpers to limit the travel in bumps and corners. He was mostly into live axle Trans Ams and Camaros. You know, old crap......Maybe ill need to read it again.
I put as wide and as sticky a tire as I could fit on my car. the result was the grip made the suspension feel weak. it couldn't keep up with the grip from the tires and the result was extreme body roll. I raised the spring rate to match the grip levels better and it feels better. on bumpy tracks I need to have the bump setting on my dampers at full soft or I get worse breaking.
This video is very subjective. Each has advantages, but for street driving, stiff and low allows for better handling and more grip through turns. The best case for soft springs is in rally racing, where the springs are very soft, but very long. That allows for the car to have a low stance (low center of gravity), but keeps the tires pushing to the ground despite all the dips and bumps on the uneven surface. That's just my two cents. Great explanation though.
IMO it would be better if you had started with pure definitions of different vehicle motions (Heave, Pitch, Roll, Twist ....) and from this point you can add more to which motion you are considering. For example you have mentioned in the reasons why to use stiff suspension ((which still undefined which stiff motions you are mentioning)) is to reduce body roll ! As mentioned in some comments you can stiffen roll mode with for example U-bare connects the end wheels and still have soft coil springs per corner.
I love your videos! I'm going through the pre-engineering classes for math and physics right now and I can only hope to remember half the stuff you explain. lol
This would be much more accurate if you included tire physics in your explanation. Sure, soft springs will give higher max grip in a car under steady state longitudinal acceleration but the moment you turn the wheel body roll will rob grip from your outside tire greatly reducing your max lateral acceleration. Not to mention the fact that a car with soft springs will experience all kinds of wacky yaw charicarisitibs if you take into account fore-aft weight transfer in the braking/acceleration parts of a turn. With overly stiff springs even a neutral steer car with IDEAL suspension geometry at steady state will push/spin in corner entry/exit respectively As you said, tires are everything, but the job of suspension is not as simple as "keeping the tire on the ground." A good suspension needs to keep the load on each of the four tires within their ideal load sensitivity. Finally critical damped stiff springs can avoid many of the problems you enumerated with stiff setups (see ohlins or moton street car setups).
Ref the body roll control aspect - how do anti-roll bars / torsion bars play into the equation vs. simply reducing suspension travel and/or increasing spring rate? Probably needs a "What an ARB does" explainer vid first come to think of it :D It's nice to see this stuff explained with simple maths... keep up the good work.
The problem with these videos is that it talks about the effects of a piece of suspension in isolation. The problem I have with this is that in isolation something may hold true, but on an actual car it certainly doesn't because a suspension is a SYSTEM and a complex one at that. Spring rates themselves are not responsible for keeping a tire on the ground. Their role in the suspension is to control the sprung mass (everything that the spring supports, like the chassis). They play a minor part in controlling the contact patch but ultimately that job is in the dampers (shocks/struts). Furthermore, this video does not consider ALL of the springs in the equation. Your tire acts as a spring, as do the bushings in the suspension if they are bonded rubber bushings, as does the damper (to an extent), as do any bumpstops. It's hard to consider things in isolation when the whole suspension is a SYSTEM where one change here can have five or six changes over there.
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There both more factors involved, and more reasons for stiffer suspension. A major factor not discussed are the shocks. In the example above, the rate of wheel movement towards the ground (for the dip) did not factor in the shocks (rebound), nor did the bump example for the stiff spring. It is complicated.
Beyond that, stiffer springs help prevent body roll/lean and help keep the tire flat to the ground. Soft springs allow the body to roll, which changes the effective camber of the tire. If you compensate by adding static negative camber, this sacrifices straight line braking... stiffer allows for less static camber. And, stiffer means generally less tire wear (which is a major factor in racing, either for cost or for stint length.)
Finally, stiffer also is important for transitions from left turn to right (and vice-versa). Soft cars allow the body to roll from one side to the other and for that to be a large and slow transition. Stiff springs prevent the roll in the first place and switch to the other side faster. Stiffer tends to stabilize more quickly after sudden transitions.
So, its quite complicated. There is no best. Generally, for smooth tracks, stiffer is better. Generally, for bumpy tracks, softer is better. (Those comments are to be taken relatively to each other.)
Last but not least, driver preference/confidence vary a lot with how the car feels - some like stiffer/firmer (springs and shocks) and some like softer. So while the engineer may say one way or the other is technically or theoretically better, the driver may feel (and perform) better with a different setup.
Thanks for considering a complicated and interesting topic.
Summed up perfectly.
agree
What about Citroen DS cars? They drive as if they are floating over the road and yet they turn as if they have stiff suspension! How do they do it?
Good comment
Learned a lot between the video + this rebuttal. Thanks for the concise write-up!
"We've got two cars driving. They're about to collide which is unfortunate, but that's irrelevant." LOL
Watching the video again... still interesting 😂
LMAO.. . Was reading this comment as he said it.
Lol, correct! Hahahaha
Very factual as always..
Wait, that's Mr. Vortex radar
"We have two cars driving. They're about to collide which is unfortunate..." This cracked me up. Probably because i am quite tired, but still, i thought it was funny that he found that worth mentioning. lol
Kaelin the Sergal Dragon Made me laugh indefinitely
"They're about to collide, which is unfortunate, but it's irrelevant" LOL
irrelevant xD
was staring at his collar the whole time
lmfaooooooooooooooo
+Wake Boarder replay*
here for this comment. It bugged me more than it should
lol
I laughed so hard at this xD
I've always loved Colin Chapman's philosophy in car suspension design. Softer springs with long suspension travel always make for a better ride and better grip on rough roads. The main reason why mass production cars are given stiffer springs is because people have the tendency to rely on their perception that cars that roll are more likely to lose grip on a fast turn.
Cars that roll don’t handle as well, it’s a simple fact..also we don’t drive at freeway speeds in cars off road, he seems to forget suspension settings are able the road surface your driving on,which dictates the suspension settings which work best..off road a softer longer setting is best , on a road course it’s a different beast, and even then having a adjustable setup is best
I seriously appreciate someone who can breakdown a subject and explain it clearly thanks @engineeringexplained
Did you say "clearly"??
When they say "it's not rocket science"
Yeah... You understand.
Soft if you can handle the roll, since a soft suspension means grip. I've noticed that in some cars, just upgrading anti-roll bars and adding sticky tires improves the handling a much greater amount than when a lowered and stiffer suspension was added.
Unbearable Pain I disagree. Some people say the primary roll stiffness should come from the springs, not the sway bars. The sway bars reduce the independence of the suspension.
TassieLorenzo True, but in big V8 muscle cars the suspension isn't independent anyways.
TassieLorenzo totally untrue... wheel indepenence ist not nessesarily a good thing. the myth that stiff suspension and hard dampers are a good thing comes from formula 1. in formula 1 you want the car to have the same attitude to the road at all times to maximize downforce. "mechanical grip" is irrelevant in F1. but since a roadcar has no downforce soft suspension will be better. thats also the reason why for example ralleycars have really soft suspension compared to for example f1 cars even when the are driving a tarmac ralley.
MrBusunglueck "but since a roadcar has no downforce soft suspension will be better. " Then why do road-based race cars with no downforce have stiff suspension? ;)... I agree there is such a thing as too stiff, but driving some road car on a track day with Hoosiers and using stock comfort-tuned suspension will give a terrifying wallowy feeling and feeling of lack of control. There is a REASON after all why PROPER sporty cars like Renault Megane RS, Civic Type R, Lancer Evolution, indeed Ferrari F430, etc all come with relatively stiff suspension.... surely? ;)
TassieLorenzo
the thing is... racecars with no downforce dont have stiff suspension. the reason why all sportscars are stiff is cause thats what people want. the nurburgring laptime off the current 911 turbo s for example was set with the dampers in comfort mode. the nurburgring is a bumpy track, but still that says a lot for me.
2 more reasons why stiff springs work well on the track:
1. To give a driver better feedback with regard to surface changes or communicate tire compliance with the road. So if you hit a spot of gravel vs ice you can feel the changes.
2. Also with higher speeds on a track, impacts from road surface changes or even suspension movement due to braking or cornering causes more travel and uses suspension compliance forcing the shock to operate outside of it's optimum stroke. So stiffer suspension is needed in order for the components to handle higher speeds. Granted your tires still have to be good enough to generate the traction needed to allow for it's proper operation or you can loose more traction because of the loss of compliance.
I am a bit confused. If we are just looking at spring rate, why aren't we looking at a spring that has enough travel to reach the 20mm? In that case the stiff spring would win, the only reason it loses is because it runs out of travel and gravity has to do the rest as you mentioned. I guess the video is not about preloading the spring and the only source of compression is vehicle weight.
If it was preloaded (as almost all passenger cars are, and why spring removal has to be done carefully even when the wheels are lifted off the ground), then the stiff spring should have ~10X faster ground contact in the dip. Your point is very valid on the bump force though.
davetek490 The amount the spring compresses is based on the weight on it. A stiffer spring will compress less, and thus have less travel.
10x faster ground contact? Nope, the math says otherwise (even in the portion where there is still travel remaining).
Engineering Explained
For the sake of being devils advocate I'm assuming a preload to allow stiff spring to travel 20mm. The stiffer spring has higher F/mm.... if F=ma, then if both springs are allowed to travel the full 20mm, at every mm of travel, the stiffer spring has more force. if a=F/m and m is constant, a is linearly higher with respect to F.
I must be missing something.
davetek490 The thing you're missing is that as the spring releases (look at the graph I drew) the amount of force it presses decreases (rapidly with a stiff spring, slowly with a soft spring). The maximum force both springs press is the same, but the soft spring will press with a greater force for longer (it does more work).
Engineering Explained
Ok, and that's only true in the case where the only force used to preload the spring is the 1000kg car. I get you, I think we're just using different initial conditions. Thanks for the explanation.
davetek490 a soft spring will make the car bouncy when the mass of the car is moving, like when you go over a crest. to stop this you ned a shockobsorber to steady out the pressure on tyres to keap traction. does a soft spring not need a harder obsorber with gives a harder spring some advatage when it comes to travel? great explanation on springs, very intresting
Every time I watch your videos like this one, you just make me want to keep my car stock, and just learn how to drive what I have better. So thanks for saving me money lol.
Stock is general purpose needed, except you're a special driver 😁.
how did i get here from gordon ramsays kitchen nightmares?
No idea, but I can start yelling loudly if it will make you feel more comfortable! :)
Skip M what are you even talking about lol?
Brandon Inu is the slight accent
What the F*** is this?? you call this a suspension??...DO IT AGAIN and this time make it STIFF
They have a passion for what they do
When you add the effects of compression and rebound dampening (oil damper), this gets much more complicated than just a spring with no damper. In fact, a spring alone does a terrible job of keeping the wheel on the ground.
Playing with dirt bike suspension in the good old days of Motocross (using about 12" of travel), I found I actually got a plusher ride with a stiffer spring (front forks, and very little preload on the springs), that still resisted big bumps with less compression dampening, and more rebound dampening (assuming the dampers were set correctly with the stock springs).
As for the preloaded travel of a dirt bike, you pretty much want your suspension to have eaten up about 33% of the total travel with you on the bike, no matter what your spring rates are, and that is adjusted by a preload ring that compresses the spring.
But, if you add the dampening,--I bet the math work goes up exponentially---but it still has to work as well in the real world, and will need field testing to fix.
Sophisticated suspension, (depending on the demands and severity of the application), seems to be one of those things that almost never comes off the drawing table very well.
You should look at some of the front forks of MX bikes today. Nobody knows how to adjust them, there are so many knobs and air chambers. But one fork on Yamaha the kabaya (sp) SSS forks, that is over 10 yer old technology, and still uses a spring, romps them all in overall performance and probably every category.
You post great stuff young man. I hope there are more like you.
Top 5 best car channel on RUclips, hands down. The content value is amazing compared to most car channels.
If this dude built an entire car himself it would pull 4 lateral Gs and have a top speed of ∞
+Rough Muff No I don't think so, he would just understand why it wasn't that fast!! LOL.
Wet Towelette god damn.. this comment actually made me laugh out loud. Laughed more than I should and I dont even know why.
if he entered a race series he'd win, with no team.
If he wanted to bottom up design a car, I would help fund the dude. Guy should start a kickstarter collaborative with other car guys and design and build an affordable sports car that can be mass produced.
Why? He's just doing the same kind of engineering that's made at the factory. The output in that case would be a really nice, well engineered premium car, nothing out of this world.
4 those of u who didn't fully understand. What he has explained is the perfect formula to base a suspension set up "coilovers". Thanks to this man and his video I understand completely on how to set up my car the way I want it. There are an infinite amount of spring rate set ups. What it comes down too is your own style of driving to formulate a functional set up for both street and track "AutoX". I'm headed in that direction. I want the best of both worlds because math makes that possible. Thank you for your injenuity.
you should've just yelled "soft!" and then stared at the camera for 4 minutes.
+Nicholas Wilson Science and engineering are about the "whys", not just the "whats". In other words they're about understanding, not just knowing.
0:28 that made me laugh harder than it should have...
PotatoadZ 0:29
0:30
0:24
There is a very important point you missed, if not the most important.
Roadcars are optimized for straight line rolling where load is equally dstributed to both sides of the car. Racecars are optimized for cornering where load is shifted to the outside wheels. So you need to calcualte spring stiffness and damping rate to that amount of load. when you corner with a soft spring, you lose alot of suspension travel right at the start because of body roll, thats because the springs are too soft for that scenario. with a stiffer spring you optimize for higher load, giving you less body roll and more suspension travel remains available mid corner. higher damping rates need to follow the higher spring rates in order to prevent unvanted body oscillating movement.
great video as usual
but you gotta also count/add that stiffer setup enables car to react faster to driver inputs, especially during direction changes (which is what racing is about)
Not drag racing.
I'm surprised people actually still debated this. This was spot on to what I learned in school. stiffer suspension for street driven cars isn't always better. example: I had a 7gen galant that I threw springs (1in front/rear) and adjustable shocks on. Hard cornering was great, but the overall quality wasn't great, especially in the rain. I went through alot of trial and errors before I figured out that soft is safe.
You should do a video on air suspension
There're 3 basic things who affect each other: Range of spring, spring rate and the shock absorber.
Particularly the shock absorbers have to be well matched. For example there are high- and low-speed compression/rebound-stages and also the viscosity of the damping oil matters.
I used to race superbikes and the suspension settings always had me on the fly, it depends on temperature and surface conditions you will use, for normal street use you can set a medium setting it will get the best of both sides from soft to hard, it is quite tricky to find the right setting at the beginning, but you will get use to it.
i’ve never gotten confused quicker than watching this video
Roll is grip, if you can control it. Can't remember where I heard that the first time, but it's catchy and quickly explains the effects of spring rate.
Zoinks, this guy's spooky smart, scoob...there's like, no way i can keep up.
i wish i had a ham sandwich to like, calm my nerves man...
Too many hash scoobie snacks
Playboysmurf1 straight off the tree in my house
Dammit. .. I read this like Shaggy in my head.
Pan tera LMAO
Pan tera 🤘🏽Pantera🤘🏽 kicks ass
This actually helps me a ton with my mountain bike, this makes suspension sag make a ton more sense.
"They're about to collide...so that's unfortunate" hahaha😂😂
Jason, first off, a big fan thank you for making these
videos for all of us to better understand the engineering behind cars and
suspensions, they have been a big help for me in understanding what parts I
might invest into my ride. I wanted to ask a clarifying question about the
video, which is in reference to the drop that the wheel would have into the
hypothetical pothole you discussed in this video. I understand what you were
trying to say in the aspect of the importance of keeping all 4 tires on the
ground as much as possible and with as much force as possible as this is the
point of a suspension. However, what I am struggling with is understanding how
the stiffer spring, that only compresses 10mm, would have a harder time hitting
the ground compared to the softer spring that compresses 80mm. I struggle with
envisioning this as being something that follows other aspects of physics, such
as the overall weight of the car, and the speed as to which the wheel hits the
bottom of the hypothetical pothole. If the stiffer spring only compresses 10mm
and the pothole is deeper than 10mm then that would leave the assumption that
the spring does not decompress further than 10mm, which when a car is lifted
there is full droop in all 4 wheels, which is in response to the shocks and
springs being fully extended and not being under pressure. For what you were
saying in the video that the stiffer springs would not either reach the bottom
of the pothole in the time that the softer ones would reach would also be
assuming that the shocks are not factored into this statement because if what
you were saying was the case then a car’s wheel would never experience full
droop and would return to the base ride height + the decompression of the
spring (10mm). I am confused because the speed as to when that wheel would hit
the bottom of the pothole would also be dependent on the speed of the car
moving forward + the speed of gravity as the car is being pulled down to the
bottom of the pothole. It would sort of question also the speed difference
between the spring decompressing and the speed of gravity (both forces would be
happening simultaneously, the car falling and the spring decompressing). It
also brings into question the force that would be impacted on the fall as well
and looking at the spring rate to determine if the car’s force from the fall
and momentum would cause the spring to compress more, thus potentially leading
to bottoming out. As I see it, and I could be wrong, we have 3 forces in this
hypothetical situation (the shocks, springs and gravity) and in “forces” I mean
all things that would cause the wheel of the car to move downward in the event
of driving over a pothole. All 3 would need to be taken into consideration when
discussing the cons to stiffer springs, correct?
Michael Capozzi is this a poem?
Very good explanation ! As you know & have to keep it simple for the layman . Shock absorbers , sway bars , bushings & tires etc. are also components of a suspension system & on the track , settings are softer in the wet vs. racing in dry conditions . Thanks for helping alot of people by posting this video !
For some that may not know the numbers used are specifically to show his point and are quite exaggerated compared real life. For ex he uses 1000kg of force but my entire car only weighs about 1200kg and you would never change your suspension by a factor of 10. Great explanation and the number make the calculations clean and easy to understand which I applaud just want the audience to know changing your suspension isn't going to wreck your car going up/down a 10mm gap.
One thing he didn't address is that softer springs will allow the unsprung weight of the wheel to induce further suspension compression which can cause the tire to lose contact with the road for a longer period of time as it goes through the compression and rebound cycle. A badly washboarded road is a good example. If your soft springs allow the wheel a greater range of motion and a slower rebound, you will have less braking and turning traction with that wheel. If you hit a series of consecutive bumps the tire can bounce up and down on the road like a basketball. No tire has grip when it is in the air. You can compensate with stiffer shocks, but the shock and springs should be changed simultaneously or either can wear out prematurely. This is why it's a bad idea to add lower (shorter) springs while keeping the same shocks. They must have similar driving and handling characteristics and capabilities.
+Chris Ashcroft This is not correct. On a washboarded road the tire will maintain contact much more with a softer spring than with a stiffer spring, which will bounce the whole car. The reason this is true is demonstrated mathematically in the video, as the force pressing down on the spring will remain greater for whatever amount of travel there is in the spring. Think about a car with no suspension (aka, infinitely stiff springs). In this case, as you hit any bump, the entire car is forced up (and the tire loses contact). If the spring is super soft, the suspension travel will absorb the bump, and the tire will maintain contact with the road.
+Engineering Explained
For a very stiff spring, yes, but what about a very soft spring?
Now the spring is under control of the dampening (compression and rebound dampening), to help the tire follow the road. But, for a hypothetical example, if the spring rate is soft (or not hard enough to rebound quickly), over stutter bumps, the shock could actually "pack" up into it's travel, because the next bump and next bump and the next bump compressed the shock more, and more, and more, until the spring rate is in a stiffer range of motion or the suspension bottoms out. When that happens, it could act a lot like a overly stiff spring, forcing the chassis upwards.
Selecting the correct spring rate for your application is probably more important than getting the dampening dialed in, but they have to work together, and it is usually futile to try to tinker with dampening if you have the wrong spring rate.
I learned something during the dirt bike suspension evolution from about 3" of travel to about 12" of travel. It was not always the longer travel that made a suspension perform better, but how well the spring and dampening handle the travel you have.
+Chris Ashcroft not only am I an engineer but I drive washboarded unsealed roads every day. I have two identical cars (GC Mazda 626s). One is turbocharged and my toy on the track with correspondingly stiff suspension. It is a nightmare to drive on these roads. My carburetted daily driver has very soft suspension with a high spring rate and glides over these surface imperfections with ease. When cornering on these surfaces it is much more stable than the track designed one.
the rx-8 has a much softer suspension then the fd 7 for exactly that reason. it's almost unbelievable how well it mantains grip. damn fast in the real world, but not so much on a race track. that's one of the main reasons why i didn't buy an s2000.
there also is the benefit of a smoother ride.
WRC cars have softer springs on tricky gravel tracks ans stiff spring on tarmac mostly. i agree with this guy. there's a lot of accidents with cats super 7 and lotus elise on mountain tracks due to the very stiff suspension configuration, its so stiff and short that the wheel cant fill the whole gap during a depression. result, lack of traction. mountain roads work better with medium spring rates, gravel with soft and corsa with stiff. it all depends of the amplitude of the irregularities. short amplitude, stiff, long amplitude soft.
springs....coils of metal...thats it..... I gotta say, the half course of physics I took, the most amazing thing to me was how refined the concept of a spring is. So simple and so useful. I just love this stuff. Great video! I wish I knew more. Guess I gotta go take a full physics course next....Thanks brother!
Do a video on rim offset
+Kurtis Snyder Agreed. I need to understand it better.
+TheRealDannyE The lower the offset number, the more the wheel will stick out. the higher the offset the wheel will be more in the wheel well and will be less aggressive. every car uses different offsets. So you have to choose wisely
I thought it was the other way around.
Further to the discussion, dedicated off-road vehicles typically use very soft suspensions to ensure transverse tire contact. A typical issue with hard suspensions off-road (read: Stock Pickup Trucks) is that the relatively low spring rate means that traversing a large bump with one wheel on a beam-axle suspension causes the other wheel to lift, thus reducing ground contact and traction.
Essentially, instead of absorbing the bump into the suspensions travel, that bump causes the body to lift, which then because of the low spring rate, reduces the effective down-pressure on the other wheel on that axle. A loss of downwards pressure is a loss of traction. It's for this reason that dedicated off-road vehicles like Land Rovers and Jeeps typically use very soft suspensions (or variable spring rate suspensions like air-springs) to ensure that traversing a bump does not cause a total loss of traction for the vehicle. Pickup trucks on the other hand typically use multiple leaf springs with a very low spring rate because they're primarily designed to carry great deals of weight in the pickup bed. A stiff rear spring on a pickup truck is a decided advantage when carrying load, but a decided disadvantage when used off-road. If you're serious about off-roading a pickup truck, replacing the stock springs with much softer leafs and adding a levelling air-bag can make a huge difference to off-road performance.
man, I love these videos.
I would love to see some sponsored content from Ohlins suspension on this channel. They are supposedly some of the most beautifully and meticulously designed suspension in terms of the quality of engineering and RnD that goes in to them. Plus they make them for your S2000 so you could get a set and try it out for free probably. I am interested to know how much of a difference their Dual Flow Valve technology makes on the street
I think a stiffer spring is better if tyres keeps contact to the ground, so after this point going soft will only decrease grip as it changes alignment unnecessarily like camber and toe.
I usually enjoy your videos but this one has some bad logic. This is a very very special case, which almost never occurs. That is hitting a bump larger than your suspension droop. I've had cars on 12kg and 10kg springs. Even an FC RX7 with Mcpherson front suspension of almost 1:1 moment arm with 12kg springs would have nearly an inch of droop. Don't know about you but if there's a road with that crazy of a drop, I'm not driving on it!
So following that special case you're discounting all the other benefits of stiff springs and claiming that softer springs are better for the street?
TheXdmgx7 The logic is sound. Softer springs will allow for more compliance with the road (even if the examples are exaggerated to keep the math simple and explain a point). This doesn't mean soft is "best" for the street, it's simply factual that in non-perfect conditions it will do a better job of maintaining contact with the ground. Design for what road conditions you intend to drive on.
TheXdmgx7 It becomes a problem when you consider the force on the body creating an upward acceleration from stiff springs. The back side of a 10mm bump can cause an aftermarket suspension to lose contact with the ground because the body continues it's velocity upward which drags the wheels up with it an reduces the load on the springs, which removes droop velocity.
Using an aftermarket ride height and spring perch separated adjustment coilover you can easily tune the suspension to be harsh either on the front side or back side of bumps using the preload adjustment on the lower spring perch. If you have conventional single collar adjustable coilovers this won't work because you cannot preload. For instance, i can set up my coilovers to have zero preload and thus maximum shock compression at static height, which will make it more likely for the shock to contact the bump stops, drastically increasing effective spring rate over sufficiently sized bumps and causing compression to be uncomfortable. In reverse, I can preload the spring to the point of zero shock compression at static height and as such giving the shock minimum droop travel, making the front side impact of bumps very gooshy but the back side of bumps like falling off a cliff.
So it depends on the ratio of shock length and spring rate to determine the actual road-contacty-ness of a coilover.
Engineering Explained I agree that in non-ideal(horrible) conditions softer springs will do a better job maintaining traction but you did not claim that softer springs are better for non-ideal conditions. You claimed softer springs are better because the harder spring will run out of droop if you jump a huge curb and you will lose contact.
In the real world it is VERY hard to lose contact due to inadequate suspension droop. (I'd be dead 10 times over if that wasn't the case)
TheXdmgx7 your assertions about the difficulty of losing contact depend entirely on the properties of the shock and spring combination. My coilovers can and do regularly lose contact with the ground. Engineering's extreme examples lay the groundwork for how relative wheel and chassis velocities work together. He is correct. You're just having trouble working between the extremes. In his example, wheel forces of 2g, 4g, 6g etc between the two extremes of 1g and 10g are possible. Those forces relate to how quickly the wheel follows the back side of every bump. The closer to 1g the more often the car will lose contact with the road. This can be due to spring rate, damper settings (over-damping on rebound for instance, lowering wheel velocity on extension) and of course limited droop travel (which is the problem with my coilovers).
Gregory Evans I completely agree, yet this is not enough of a reason for the claim "softer springs are better for the street."
My problem is not with the overly simplified math but with stretching it and using it as a proof for a much more broad claim.
An example would be the moose test(Real world, right?)... How do you think a softly sprung car will do? It'll be less responsive due to the delayed weight transfer. See my point?
Ok you helped us scratch the surface of understanding basic suspension physics. I think it would be great to talk about suspension setup on race cars both on road and off road that would be a very helpful video
All of your reasoning was pretty sound and the science was definitely correct. The only thing that struck me as a bit odd was that the comparison was pretty unrealistic. Nobody ever puts a spring that's 10x higher in spring rate while using the car for the same application ie. street driving etc. Typically, I see most tuners and companies going to a 1.5-4x spring rates depending on how stiff the car initially was and/or how much suspension travel they intend to utilize. That might have made a more reasonable comparison. Great video, nonetheless.
Ok, the thing is that stiff springs are supposed to be used on tracks, because they affect weight distribution and weight shift and also handling, stiffer springs allow more weight to be charged on them without the worry of them being squeezed to death so this allows them to handle drift better allowing you to go faster, on the other hand soft springs really shines in everything else because either on track (only of you are a grip guy) or a downhill/uphill scenario you have overall better grip as well as a smooth turn, but at contrary if you want to drift you will have to go slower to avoid hitting the wall and it's easier to spin out so, on a soft spring drive grippy and safe, please correct me if i'm wrong, always looking forward to improve :)
So what's going on with rally suspension? I know they have lots of travel but are they stiff or soft?
I guess they have a "pretty soft" but not too soft springs with very very good damping
soft suspension
GrahamBartle soft springs, hard shocks and long travel.
*****
Rally drivers also slide their cars because of a technique called "late apex turning" it just allows the driver to see more of turn before having to decide if he/she needs to turn a lot or little. The body roll sounds like a good point as well for why they slide though too
lowering its not the only way to reduce body roll. anti-sway bars at the front and rear, tuned for your car, will reduce body roll maintaining the under/oversteer balance. a lot of cars of today have soft dampers with stiff sway bars.
I enjoyed the concepts provided by this video. I race as a hobby and have used stock soft to quite firm suspension setups both on and off road.
I do think you need to discuss mass and damper reactions to these forces in order to fully understand the resulting motion as you experience them in the car. I think it's a little too simplified just to talk about a spring alone.
Cars are dynamic systems. Even during steady state cornering, cars are still moving about, increasing, and decreasing applied force to the tires. For sport driving, stiffer is good in that it reacts faster. There's less time between input, settling of the chassis, and reactions. In many cases, reaction speed is a big factor in going fast. If a car is too sluggish, you might have a hard time transitioning through very dynamic sections without first slowing down a little in order to buy time for the car to react. The stiffness also can help generate tire loading forces specifically due to its ability to ramp up force via a jab of the brakes or flick of the steering wheel. Granted, the damper is playing a big roll in this while spring rates play second fiddle. Still, stiffness equals dynamic speed.
I cannot go too stiff because my city is full of "depressions". LOL
Very nice explanation why race cars have stiff suspension, but what about off road vehicles. They too have stiffer springs, and their track is by no means smooth. Thanks and keep up the good work!!
I didn't have time to watch this video, but it shouldn't be left without a like.
When racing downhill mountain bikes I tend to set my suspension up to be using about 75% travel to float over most terrain. If it is not using that much, i soften the spring rate and/or back of compression damping. The last 25% is used for g-out situations durning landings and such. Using this much suspension travel makes for an active and smooth ride.....any less and you are suffering unnecessarily and could be going faster. The only problem is that a huge compression coupled with an impact like a stone can blow into the bumpstop and dig deeply into the tire thickness often causing a pinch flat. it creates a condition where there is a huge risk of flatting but the massive amount of control will (hopefully) allow me to avoid those obstacles. Tire pressure is hugely important as it changes the frequency of the small chatter type bumps and works thoroughly in conjunction with the suspension. Tire technology has improved so much in cars and bikes that it is easier to avoid flats. This balance between compression and rebound damping, tire pressure, spring rate and rising/falling rate suspension can not be figured out mathematically and there is always a compromise. I tend to go soft and avoid big hits....I'm light and so are my vehicles. Big guys/heavy vehicles have to beef things up more and the weight begins to push heavier into the tires. I might run 30 psi where big guys will run 45-60. They handle the big hits but bounce around on the little stuff. For cars and street, set it up for where you want performance. Straight lines, or on ramps? Choppy alleys or highways? I like to be able to blow through transitions, chop and chatter with minimal fuss, smash speed bumps and humps and drive like a crazed rally driver. I'd prefer to not slow down over every rise or parking transition. I want to be able to keep up with most people on smooth but not necessary beat them in my 2800 lb truck and say bye bye over the crappy sections. I seem to get around better than most road cars and our town has terrible roads. Temperature also affects the durameter of the tires. Tuning the tire pressure is equally important to spring rate. If I were upgrading a car, I'd start with firmer/lower profile tires and then moderate spring stiffening after. If your vehicle is fairly good as it is, adjust incrementally.
this is "suspension for dummies 101". Pure basic knowledge. There is much, much more to say about suspension.
Okay sir. Congratulations. You have accurately described the purpose of this video.
The fact these videos are free is mind blowing to me. Thanks for all the info you put out there!
Of course the best question is "why not both" --- variable rate springs.
+GunFun ZS because until recently variable rate damping didn't exist.
That's true for a lot of things. It's still the right question.
+GunFun ZS Hydraulics suspension, i think is the solution
+GunFun ZS Used those on an old caprice. Car was smooth sailing, but when it came time to load up, and you can load those things, didn't have to worry about sagging or bottoming out on a big bump.
I didn't get all of the verbal jargon a but I understood what you're saying as I feel them out on the road and track having stiff spring rates on both my cars.
Seems like you just talked about compression and left out preload and rebound. Your videos are great but to explain the real reasons behind race/street suspension in 6 minutes is impossible.
Dani2wheels That's why I have more than one video on suspensions. :) Not trying to cover everything in one video, just spring rates for this one.
Engineering Explained i think the title should have spring in it instead of the blanket of suspension
AMGV Media Done!
Hi very interesting.....I could suggest that what you said about the springs in a suspension system applies also to the profile of tyres. The higher the profile the more comfortable ride. Remember road races and your skinny tyres
7 years late but... Never knew this before. Glad the algorithm is doing its job. 🙂
Progressively wound springs. Best of both worlds.
+Jack Allen nope
Since I did spend a bit of my career as a suspension engineer - for the sake of the viewers - I would like to here more about ride quality at speed and the compromise of ride vs turning handling.
Ah ha, so that's what Einstein was talking about ?!?
That may be right on some cars.
1. Variable grip level of tire through body roll ads force to the tires.
Remember you are balancing thousands of pounds on 4 small patches.
If your spring has too much play the car will only shift the the side that G forces are acting on.
Meaning understeer or oversteer
Sports cars have the set up and power to hold more G forces on a constant road surface.
This could sound bad but i prefer soft on front and stiff on the rear XD lol
***** Hello oversteer!!
TassieLorenzo Also means he can enter a corner faster, go look up suspension dynamics and you will see what going with a soft front vs a hard front does. Also oversteer is better than understeer as it can be controlled with enough practice.
TassieLorenzo Dat weight transfer though, better for braking and cornering, especially if he has an FWD car.
TassieLorenzo oversteer is better than understeer and like they are right, soft front gives you better grip on the front wheels so better conering speed
Really good video and good food for thought. The only thing I would add to this, is particular with regards to racecars as a rough rule of thumb the stiffer the suspension, both in spring and bar the more it will put temperature into the tyre. Consequently when you start running race rubber you always play a delicate balancing act between mechanical grip and ensuring the tyre is up to temp.
Is that spring rate or spring stiffness? or are they both the same thing?
+Adnan Rahman I use them interchangeably. Ultimately you're measuring force over distance (how much force is required to compress the spring 1 mm).
+Adnan Rahman I believe spring rate is about the force necessary to generate each 1mm of compression in the spring. so, the higher the spring rate, the stiffer the spring is.
Thanks for the response guys. I was just a little confused because I always took rate as something per unit of time
Adnan Rahman haha i get what you mean. i think what throws people off is that the word "rate" is often used by normal people to describe some sort of speed or change in distance over time.
here, it's really more about the spring's compression, so not much to do with time at all. glad it helped you!
Screw school, the only thing I need is your channel
As usual, this is a great video on a great subject. However, I'm seeing a lot of confusion on this topic, so I thought I'd try to help those trying to learn with a little more "real world" application of these concepts that were likely beyond the scope of this video.
Suspension set-up (and the related subject of vehicle dynamics) is a VERY complex subject. You cannot just make blanket statements like "stiff is better, bro" or "soft is faster, dude." Suspension tuning is not a binary decision between either extremely stiff or completely soft. Those arguing for either/or are missing the point.
All race car set-ups are a trade-off between COMPLIANCE and vehicle RESPONSE to driver's inputs, and that applies to everything: dampers, roll bars and springs.. The more you stiffen the car, the more total vehicle grip and traction you actually lose, but you gain improved response to vehicle direction change. You have to find the cross-over point. Too much roll and the car feels sloppy and slow to change direction. Too stiff and the vehicle will be very responsive in change of direction but you’re actually losing grip, and combined with a lack of compliance ,it will make the car slide all over the place, chatter over the bumps,etc. which does nothing but destroy the tires which just compounds the handling problems. The "correct" set-up will always depend on track characteristics and driver preference, and in the case of street car performance set-ups, a compromise between all of this and vehicle ride characteristics. I'm sure everyone has ridden in the tuned car on the street with a suspension so overly stiff it crashes over the smallest bumps and rattles the fillings out of your back teeth.
I highly advise anyone out there wanting to learn more about this subject to read the great books on this subject like Tune to Win by Carroll Smith and How to Make Your Car Handle by Fred Puhn. You will learn a lot for the investment in time.
Nostalgia. Brings back the good memory on studying the first Physics class exam and A's it.
What if the driver is 70 kg or 130Kg :D if u have soft springs and the person is heavy... than you get hard springs
I think it is personal what the driver like, Comfortable or sport drive
Driver weight generally has no impact on how the suspension performs.... You're talking a 60 kg difference in a 1500kg car.
yes maybe when the car is 1500kg then u not can see it maybe, but when i see my friend from 100kg step in his lowering car 980kg.. i see the car go more down on his side
MMD While the vast majority of cars are nowhere near that small, a 60 kg difference is still only 6% of the car. The car's stock suspension is designed to work with that kind of load and does not require a stiffer suspension.
and also when u put a big subwoofer in the trunk the car go down, so not very usefull information in this video ;)
MMD For example, in a 900 kg Mitsubishi Mirage, the suspension is designed to support an additional 400 kg in passengers and cargo.
Better is subjective based on the goal of the user. Suspension is not only to help maintain contact with the ground, but to affect how quickly or slowly the vehicle turns (provided the tires have stiff sidewalls) and the comfort of the passengers.
this is almost as true as 9/11
woah I've watched this 4 times and i still can't decide what I want for my truck. I want the best mix for daily driving and performance.
Nice job with these videos. I am an Engineer by training and still learn a ton from these short videos. Thank You for the good information
I think stiff is always better............
You think wrong, next time look video before coment.
As has been stated, in the racing world, you go with as soft a spring as possible. If a car has downforce, and is very pitch-sensitive because of said downforce, you will end up being forced to run a stiffer spring. Many of the new GT cars have front splitters designed to create massive downforce when placed close to the ground. Not only are they very pitch-sensitive, but they have to be withing a couple inches of the racing surface. Obviously with such limited ride height and pitch allowance, very stiff springs are used. For people bringing up spring splits, this is how one would balance the car. Usually, race cars will tend to like a certain spring split "window", a specific F/R spring ratio that moves together when stiffening/softening the car. This ratio can be moved slightly to affect the balance of the car in different parts of the corner. Also understand that a "big spring" will take a "big damper" to control it. This is very complex process, so please don't say things like "you can usually go with X front and Y rear". Without knowing car weight, motion ratio of the wheel, intended ride height, intended use, tire type, etc., you really can't state a spring rate.
Very good video, thanks.
I may add few things.
Lets look at stiff suspension pros & cons and we may assume the soft susp. will be reverse of these.
stiff susp.
pros: as you expressed on your video
plus, stiff suspensions allow more precise handling on smooth surfaces and they tend to more responsive to driver inputs than the softer suspension.
cons
* relatively quick tire wear
* difficult handling on bumpy surfaces and more stress on suspension members & attached points.
* not comfortable
IMHO the best suspension is.. what is the definition of the "best" btw?
Ok, let's say average "best" for the sake of the argument, it is dependent to the surface quality, road conditions, appropriateness of tires, the driver and maybe the mood of the driver :)
I think both work.
But for a stiff one you need a resistant car (frame, body, and every articulation) because the suspension is not soft enough to absorb shock so it is transmitted to the whole car.
For soft ones, the only problem are body roll, wave, lean. The car (frame etc.) is more protected cause the movements will be smothier. The soft sprint can absorb the movements as they can shape faster. Shock absorbers will not help much because if you use strong ones, it will limit the advantage you get from soft springs.
The ideal would be soft spring+variable shock absorbers able to variably absorb shocks. For example, letting the tire goes down (smoof spring) but harden and do not allow the car to be wavy once the bump is done.
If both vehicles are going to collide, it probably does not matter what kind of shocks you have
Seriously , informative video
to build on earlier comments, I would like to see a follow-on of this video not just showing the extremes of very tall soft springs vs very short stiff springs, but realistic middle ground and typical suspension swaps.
Stiffer springs help maintaining lower diving on heavy braking and turning. This is helpful because the sudden changes of load disrupt the balance of the vehicle and the contact patch of the tires. Having said that, most of the times racing cars' suspensions (that applies to bikes also) have stiffer rebound settings which actually help keeping the tires on the ground more under heavy acceleration or braking. That's why most of the times when tuning a car you don't mess with the springs instead you change the shocks. Just my 2 cents...
thanks for this video!!! very structured and well made!
one minor thing i want to add, you said beginning at 3:45 that "the softer spring presses it [the wheel] down faster". In your example both springs press the wheels down equally fast, the stiffer spring is just less mm compressed in your case. your sentence implied (my opinion) that the softer spring itself is faster. you made it very clear that the rest of the travel distance to the ground is pulled by earth graviation, but this sentence alone seems a bit missleading for me.
is this nitpicking? i hope you dont get mad over me!
i really like your videos, please continue!! ;)
cheers!
Phil Langer What I'm implying is that the wheel with a soft spring with more travel will contact the ground faster than the stiff spring with less travel. Less travel is a result of the stiffness of the spring, so they've very much intertwined.
Engineering Explained in your example yes the softer tyre with more travel would act faster but if the bump was smaller, like a race track bump of 10mm or less then the stiffer spring would react quicker, which is why race cars have those short suspension travel stiff spring setups. Also a softer spring is more compliant, easier to put power down etc however slower to react to weight shift. Understand though there are so so many aspects you can't cover it in one video. Suspension and spring setups are a fine art..
BenjiMC1 I would agree with Jason in the softer spring get's to the ground faster, even in your 10mm example. What you are neglecting is the pre-load on the springs. Both springs are pre-loaded with 10,000N but if the stiff spring experiences a 1 mm dip in the road it now only has 9000N while the soft spring (all from his example) would have 9900N. Since a=F/m the soft spring has more force with the same mass thus higher acceleration towards the new surface in the road.
In general softer suspension are better suitable for road cars which constant meets unexpected and uneven road surfaces. Race cars on race track which constantly drive at very high speed on controled flat surfaces should use hard suspension setup. Because of aerodynamic lifts and down forces effects the racer so you must use hard suspension setup to maintain the height.
Some people still don't have any clue due to the amount of softness and hardness to use for customize their own vehicle. Although not all the time but most of the time your vehicle manufacturer's engineers has calculated the best compomise settings for your vehicle's main use purpose. But randomly some owners may not agrees with his OEM setup. So if you need to customize it then you must figure out how much softer or harder than the OEM. Not surprisingly it will be trials and errors for your perfect setting. Unless you have the opportunity to full access to your manufacture's engineering faculty or luckly for you the after market supplying you an exact test mule as your vehicle.
If you still don't understand why and how, then stick with OEM can't go wrong. After all you are betting with your wallet.😇
When the car is driving at high speed, the frequency of the bump accelerates, and if the tire is to get maximum grip, the shock-absorbing system that requires a short travel schedule can follow the frequency of the bump.
Wow! I had never heard that before! I thought the purpose of the suspension was to keep the vibrations of the road from loosening bolts and ripping parts off the car!
So, you're saying that the suspension is designed to keep the car tethered to the ground! Well, I guess you learn something every day!!
( I have a go-kart with no suspension, and I am constantly having to tighten the bolts and mounts after I drive it offroad. I just assumed...)
Wow! The physics is reeel! I figured that's what stiff suspension meant, but now I have a better understanding of it. Thanks!
This is why the Alfasud was the best handling ROAD car in its time. Public roads are not flat and hole free, so soft long travel with good damping is the way to go. There is a reason why WRC cars have such huge suspension travel compared to an F1 car. Body roll is not a problem with a properly designed multi link suspension, where toe and camber are controlled. The choice of dampers is more important, getting the balance of bump and rebound matched to the spring rates and body mass.
I like Carrol Smith's advice.. Have just enough spring to keep the nose off the pavement under maximum braking load. Do the rest with sway bars. Also feels like relatively softer in bump and stiffer in rebound for the shocks seems like a good idea.
I thought I was watching mechanic stuff. This is an engineering class!
ive tried stiff/soft suspension on a corolla for street driving and honestly the only difference i can feel is the stiffness and softness of the springs. i can push the same speed around ramps and canyon curves and the tires will stick to the ground. the difference between the two for me is the feel of the car. in my case, i would leave my car with softer springs bc its convenient and does what i want/need it to do opposed using stiffer springs.
+Bee Vang I felt the same with my old corona, I felt I had more control with the softer springs on canyon/mountain roads, stiffer and the car loved to understeer. Plus stiff springs on the street I felt would wear out my chassis.
There is another factor in play - damper rate. A stiffer spring demands a tighter damper to control it at resonance. Damper rates are measured in m*sec^-1*N^-1. Tighter dampers transfer more shocks.
Yet another factor is the lowpass filter created by the spring and the mass. The tighter the spring the higher the frequency at which the filter operates. In other words the stiffer spring transfers vibration at a higher frequency into the car body, resulting in excess road noise and passenger discomfort.
The springs should be as soft as possible, but as hard as necessary. While the stock suspension of a Integra GSi is perfectly adequate for circa 1995 all-season tyres (as fitted and engineered for when it was new), when you throw on Hoosier R-compounds, probably on a 8-inch wide rim instead of the stock 6.5-inch wide rim, and take it to an autocross suddenly it's no longer as "hard as necessary"... Hence uprated springs/shocks or coilovers being required. :)
you missed one point, stiff springs can sustain the upspring mass better when you turn, that means, more overall grip capability of your tires
Ideally every motion, (ride, pitch, roll) of a vehicle should be controlled by a separate set of spring and dampers. I think it is more appropriate to say this video covers more about ride spring which control the vertical motion of the car. In general ride spring is set as soft as you can get away with that provides enough support so the car don't bottom out and don't over extend given the type of surface the car will have to negotiate. However most vehicle we see on the road are not designed with ride spring that only controls ride, but also pitch and roll. This results in a compromising situation where you can't go as soft as you want on ride while maintain high pitch and roll response like you want in a racing situation.
It depends on if you're driving on or off-road along with personal driving preference. I drive on pavement and my car has a low center of gravity, wallowing like a pig doesn't do anything good for steering compliance - so stiff is the way I prefer it. It's more manueverable and responsive. If I liked driving trucks I'd probably have a different opinion.
Of course these days many cars are made with variable-rate springs. An attempt to split the difference for the best of both worlds.
Herb Adams (has a book, chassis engineering) said IIRC, soft springs, stiff shocks, big sway bars and used big jounce bumpers to limit the travel in bumps and corners. He was mostly into live axle Trans Ams and Camaros. You know, old crap......Maybe ill need to read it again.
I put as wide and as sticky a tire as I could fit on my car. the result was the grip made the suspension feel weak. it couldn't keep up with the grip from the tires and the result was extreme body roll. I raised the spring rate to match the grip levels better and it feels better. on bumpy tracks I need to have the bump setting on my dampers at full soft or I get worse breaking.
This is an amazing video. I wanted give my car a much smoother feel when I'm driving on dirt roads.
This video is very subjective. Each has advantages, but for street driving, stiff and low allows for better handling and more grip through turns. The best case for soft springs is in rally racing, where the springs are very soft, but very long. That allows for the car to have a low stance (low center of gravity), but keeps the tires pushing to the ground despite all the dips and bumps on the uneven surface. That's just my two cents. Great explanation though.
IMO it would be better if you had started with pure definitions of different vehicle motions (Heave, Pitch, Roll, Twist ....) and from this point you can add more to which motion you are considering.
For example you have mentioned in the reasons why to use stiff suspension ((which still undefined which stiff motions you are mentioning)) is to reduce body roll !
As mentioned in some comments you can stiffen roll mode with for example U-bare connects the end wheels and still have soft coil springs per corner.
I love your videos! I'm going through the pre-engineering classes for math and physics right now and I can only hope to remember half the stuff you explain. lol
My brain hurts, but a great explanation Jason. For some reason I'm craving Fig Newtons now. ;)
This would be much more accurate if you included tire physics in your explanation. Sure, soft springs will give higher max grip in a car under steady state longitudinal acceleration but the moment you turn the wheel body roll will rob grip from your outside tire greatly reducing your max lateral acceleration. Not to mention the fact that a car with soft springs will experience all kinds of wacky yaw charicarisitibs if you take into account fore-aft weight transfer in the braking/acceleration parts of a turn. With overly stiff springs even a neutral steer car with IDEAL suspension geometry at steady state will push/spin in corner entry/exit respectively As you said, tires are everything, but the job of suspension is not as simple as "keeping the tire on the ground." A good suspension needs to keep the load on each of the four tires within their ideal load sensitivity. Finally critical damped stiff springs can avoid many of the problems you enumerated with stiff setups (see ohlins or moton street car setups).
Ref the body roll control aspect - how do anti-roll bars / torsion bars play into the equation vs. simply reducing suspension travel and/or increasing spring rate?
Probably needs a "What an ARB does" explainer vid first come to think of it :D
It's nice to see this stuff explained with simple maths... keep up the good work.
The problem with these videos is that it talks about the effects of a piece of suspension in isolation. The problem I have with this is that in isolation something may hold true, but on an actual car it certainly doesn't because a suspension is a SYSTEM and a complex one at that. Spring rates themselves are not responsible for keeping a tire on the ground. Their role in the suspension is to control the sprung mass (everything that the spring supports, like the chassis). They play a minor part in controlling the contact patch but ultimately that job is in the dampers (shocks/struts). Furthermore, this video does not consider ALL of the springs in the equation. Your tire acts as a spring, as do the bushings in the suspension if they are bonded rubber bushings, as does the damper (to an extent), as do any bumpstops. It's hard to consider things in isolation when the whole suspension is a SYSTEM where one change here can have five or six changes over there.