PLEASE continue this series. You're the only person who explains not only this precisely, but who provides quantification. I'm hoping through trawling what you have created that I can find something on heave spring / 3rd element. So far, I've yet to see a good explanation. But I'd settle out of court for explanations on shocks, ideal suspension stiffness, and of course, you probably know better than I what things most people either don't understand or (worse) falsely believe they do understand. I can only imagine how busy you must be (assuming you're an ME), but you'd easily develop a channel far larger than Engineering Explained. You're just a better teacher. I see you've done a few on braking which I think I'll watch first. I think most people misunderstand brake hardware, and assume more pistons, cross drilled, and larger radius equals greater clamping pressure, provides needed ventilation and greater leverage for stopping. If I'm not mistaken, the usual problem is adequate thermal mass in the heatsink and rate of heat removal afterwards to avoid fade ... which can be accomplished either through larger radius or via thicker rotors. In which, I'd assume a thicker rotor would be superior: Providing slightly less angular inertia / momentum. Provided the existing calipers have the clamping force to lock up the wheels at the highest top speed, ,additional pistons aren't needed. And cross drilled are just opportunities for cracks ... if any machining should be done, gas slotted is preferable. But all things being equal, the lightest caliper that provides _adequate clamping force_ for the peak angular momentum is the proper sized rotor. In order to need more clamping force, you'd either need to stop the same angular and linear momentum, or, have increased traction via grippier tires and downforce. Otherwise, most bigger brakes (especially on lighter weight cars) is a vanity purchase / cosmetic. What I really want to learn more about / understand is bump & rebound (shocks), and how to make them work best. And of course, the aforementioned physics of heave springs and their limitations: Can it reduce only a percent? If so, what's the upper limit? Or can it eliminate an axle's squat completely ..? I wish you were local. I'd love to work with you creating content. I honestly think you could be a "youtube star." As in ... get manufacturers offering you loaner vehicles for articles, and ultimately income. Not only do you understand your field, but you're an exceptional educator. If you're interested ... please contact me. same username at google's mail. I think I could help with a few things: Content ideas, editing (i'm not great but I don't mind putting the work in) ... and as someone who doesn't know much, I think it's kinda difficult for people who know things to remember what it's like to not know, and to know when they've adequately explained to the weakest link's pace. I can be that weakest link. :) (so weird that more companies aren't looking for my amazing skill). And if not, I'll just enjoy watching your content. Thank you again for your generosity of time and knowledge.
Great stuff. I didn't know about the distinction in anti-squat with IRS vs live axle, and the explanation of AWD vs RWD was also new for me. Anti-squat is something I want to look at on my BRZ. Common wisdom in the community is that it has too much because its rear suspension comes from the Impreza.
Just stumbled onto your channel, you're doing a very good job! One thing that confused me though, if you look at Race Car Vehicle Dynamics page 631, it seems you don't find the instant center by drawing lines through the chassis mounts, but rather the continuation of the A arms untli you're laterally in the center of the wheel. I.e. with parallel wishbones, your instant center would be correct, but with the angled upper wishbone, the upper line would be offset vertically, imagining the upper wishbone to extend all the way until the tire center line, and your instant center would be a bit further to the left.
Niels, Yes, that is correct but it really only becomes an issue if the sideview angle of the arms is very severe which it rarely is. With more conventional arm angles, the error is small and can be ignored. To me, what it really points to is that the second method, which looks at the motion of the contact patch, is really the preferred method and it is what is done by all multi-body dynamic software systems that I have used. It's far more accurate and doesn't care what the suspension architecture is.
@@suspensionsexplained Thanks for your reply! I like how you present it, the sliding pin example as well. Hope you get more views in the future. There is a lot of popular superficial vehicle dynamics on youtube, often including mistakes, so it is refreshing to see your stuff.
Good question. It would certainly be different. The way to think it through is to picture the vehicle up against a wall. Apply torque from the engine and see what happens. The car can't move because of the wall so the engine just torques up the wheel. In a normal independent suspension, the wheel would try to turn but couldn't because of friction with the road. the result is that the engine torque just tries to push the suspension forward at the wheel center. With a portal axle, you still have the force pushing the wheel center forward, but there is also the gears in the hub where the gear attached to the input shaft is trying to "walk" around the gear attached to the wheel, so there is a moment being generated inside the knuckle/hub. The size of that moment also depends on the gear ratio of the portal axle and the type of gears: is it a simple two piece gear reduction or is it a planetary set, in which case the input shaft may actually spin in the opposite direction compared to the wheel. All of these factors would influence how the anti-properties would be affected by a portal axle setup. Sorry, there are never easy answers!
I’m glad Matt recommend your channel, you explain things well. How do the principles apply with leaf springs and traction bars on a straight axle car? I understand the traction bar is really to keep the spring from wrapping up. Would you move the front spring eye up or down to adjust anti-squat? Also how would the regular spring shackles vs a slider at the rear of the spring affect the anti-squat.
The principles are exactly the same. Keep in mind that with a solid axle, the line needs to be drawn from the tire contact patch, not the wheel center.
The Yamaha Tenere 700 utilizes anti-squat. Front wheel traction is important when riding motorcycles off-road to steer/counter-steer using throttle. Helps alleviate rear suspension from compressing and rebounding too quickly, causing a highside crash which can launch the rider clean off the bike.
Hello! Could you please elaborate more on why the reaction point is different between live axle and independent suspension? I am doing a research, if you can please point me out if you know literature which expands on the physics behind this. thank you very much
Excellent explanaition, even though200/25 is not 80, 2000/25 is, so i understand what you mean! Kgm ( kilogram meter is a very good definition of torque, 1kgm=1kg, one meter from center of rotation.
What is the advantage to a geometry that squats in an independent rear suspension, rear drive car? Does it make acceleration out of a corner more controllable or predictable? I know that a drift setup often shifts weight to the rear wheel opposite the slide. For grip racing why would any car be setup to increase squat on acceleration?
hello sir can you post a series on DESIGNING A SUSPENSION GEOMETRY FOR A FSAE CAR - DOUBLE WISHBONE, DAMPER TO LOWER ARM TO BODY or PUSH ROD SUSPENSION, I will be waiting sir i request you sir
No, the ideal line is drawn to the tire contact patch only with solid axles. With independent suspensions, the line is drawn from the wheel center. Always drawing it from the tire contact patch is the mistake many people make.
There is something that does not make sense to me. You describe 100% anti-squat as "completely cancelling out weight transfer". My understanding of weight transfer is the reduction in normal load of the front tyres and corresponding increase in normal load of the rear tyres under acceleration, which occurs for the reason you explained at the start of the video, with the moment created by the CoG being some non-zero height above the contact patch. I can see how 100% anti-squat will mean that no compression of the rear suspension springs (and corresponding extension of the front suspension springs) will occur- the vehicle will remain completely level during acceleration. However I cannot see how this can change the normal load on the tyres themselves. If we treat the wheels and body of the car as a whole system, the free body diagram you drew at the start of the video still applies- any forces that occur within that system must cancel each other out. Alternatively, looking at the system as the body and wheels separately, if we consider your wheel with a pin moving in a slot, if the wheel pushes the body of the car up due to the angle of the slot, the body of the car must push the wheel down with an equal magnitude force. In other words, the load transfer, and therefore ultimately the normal load "felt" by the front and rear tyres has not changed whether we have anti-squat or not. I understand that there will be a caveat to this, that the amount of anti-squat will to some extent change the motion of the CoG itself in the car's reference frame during acceleration, but I imagine the effect of this on load transfer is low. Please let me know if I have understood this correctly and thank you in advance!
You're understanding is spot on. As you noted, the amount of weight transfer is independent of the anti properties of the suspension. It is simply a function of the mass of the vehicle, the acceleration, the CG height and the wheelbase. Nothing else. You are also correct in assuming that the motion of the body as a result of squat and lift will have some impact on the height of the CG, and therefore the weight transfer, but the effect is minimal. Similarly, 100% anti-squat in the rear suspension also will have no impact on the weight transfer, only on the way the suspension reacts to it. But it will only impact the way the rear suspension reacts to it. It can have no effect on the front suspension since in a RWD car, the front has no acceleration forces to help counteract the weight transfer. The front will lift in response to the weight transfer no matter what is happening at the rear. Having 100% anti-squat simply means the rear suspension will not deflect in response to the weight transfer. That is all it does. I hope this helps.
This video illustrates a solid axle real differential but that setup is omitted from the roll center video. Does anybody know of a good video about the rear roll center with a solid axle and panhard bar? Thanks
I have never designed a suspension for a race car but I have talked to people who have. The general feeling I have heard from them is to keep the amount if anti properties to a minimum. That way, you can control the way the car moves with springs, dampers and anti-roll bars. If you have a lot of anti properties, and this includes high roll centers since those are in reality anti properties in cornering, reduce the amount of force traveling through the springs. This means that spring changes have less impact on the way the car handles since they have less force to work with. Think of it as a signal to noise ratio. Having as much force traveling through the springs during cornering, braking and acceleration means you have more "signal" to work with when it comes to tuning the suspension. Also, anti properties mean that the weight transfer reaches the tires sooner because you're not waiting for the body to react and move before the force builds in the tire. This may cause changes in the loading of the tire contact patch that may be too quick for the tire to handle. I can imagine a slower build-up of tire forces meaning that any over or understeer that would happen as a result of the weight transfer would happen slower and be easier to catch and manage. I'd love to learn more about this if anyone has any thoughts or experiences with it.
I've been told that independent suspension cannot have strong enough anti-properties (particularly anti-squat) without making other responses like the roll centers and various geometry gains far less than ideal. Is this the case, and if not, which independent suspension designs are there that can be used both front and rear that allow you to independently control as many responses as possible?
The instant centers are independent of other properties like camber gain, toe change, or roll center height because those are properties that happen in the other dimensions. i.e., camber change happens in the rear view, toe change happens in the top view while the anti properties happen on the side view. Since they are effectively orthogonal to each other, you can independently control them to a large extent There are limits of course, but they are at the extremes. Most independent suspension designs give you the ability to control these factors independently.
@@suspensionsexplained How much anti-squat do you think a designer should go with in a street driven performance car? I've read that you don't want 100% because then the driver doesn't feel right when the car accelerates, but at the same time, it's demonstrably better to have some anti-squat for forward acceleration. Also, over 100% can do weird and messed up things, correct? All that aside, I also just watched your video on anti-dive and lift... Is it better to prioritize high anti-lift even if you DO end up getting weird 100% or more anti-squat, or should you get your anti-squat correct and then just accept whatever anti-lift that gives you? Also, is the instantaneous radius method also better for anti-squat calculations, or is the geometric method typically more viable here than it is for anti-dive/lift?
Congratulations on recognising this. Squat and dive are simply positive and negative pitch. The pitch centre is found in side view in exactly the same way as the roll centre is found in cross section.
Yes and no. The roll center is always found with lines drawn to the tire contact patch. My point here is that for anti-squat, you sometimes need to go to the contact patch and sometimes to the wheel center, depending on your suspension and brake system architecture. Too many people seem to think you always go to the contact patch and that is not correct, as I described.
Hi Hubert, Thank a lot for your video I finally understood why force would apply at CP on a live axle. 👍 I have one for you: If the car you draw @6:20 is a RWD with a live rear axle, it would have 100% anti squat. So no squat on power, right? Now if you draw the Side View Instant Center of the front suspension, the intersection of front and rear SW IC will be the pitch centre, right? It is totally possible that your pitch centre locates way below the Suspended Mass CoG... So then if you have a pitch moment, how can you not have squat?🤔 The way I feel it, is that anti effect work according to this definition only if one axle is connected... Laurent
Laurent, The front suspension IC would only be relevant if there is also drive torque going through the front. But in a RWD car, all the drive torque is going through the rear so there are no forces being applied on the front to help counteract the lift that happens on the front during acceleration due to the weight transfer. That is why on a RWD car, the ideal line does not go through the CG but instead goes through a point at the height of the CG above the front wheel centerline. Remember, the pitch moment comes from a horizontal force acting at the height of the CG. It doesn't care where the CG is longitudinally. It only cares about its height above ground.
@@suspensionsexplained Hubert, I agree but that's not my point. Let's take this example: Say you design a RWD car with 100% anti squat. Make it accelerate from a stop at 1G Will it squat? supposedly No..... Design the front suspension so that the Pitch axis is well below the SM_cg. Now you have a car with 100% anti squat but also a consequent pitch moment arm. Make it accelerate from a stop at 1G Will it squat?
No it will not squat, but the front will lift. "Anti" properties (anti-lift, anti-squat, anti-dive) work because they take the horizontal forces (from acceleration or braking) and convert them into vertical forces which counteract the forces from weight transfer. So, if there are no horizontal forces then there cannot be any "anti" forces. What this means is for a RWD car, the front suspension design has no impact on the amount of squat that happens in the rear. All the front suspension does is react to the weight transfer since there are no horizontal forces to counteract it. This means the IC of the front suspension or where it crosses the IC line of the rear suspension is irrelevant. It doesn't matter if this intersection is below the CG or not. All that matters is where the IC line from the rear goes since that is the only place where acceleration forces are coming from.
The pitch axis is relevant during braking because there are forces coming from both the front and rear suspensions. It can also be relevant during acceleration in an AWD situation but then the lines need to be drawn correctly considering which suspension is a live axle and which one is independent.
Thank you for your video, i do have a question, would Anti-Squat affect grip or not? if yes/no, how and why? by common sense, it seems that if there is Anti-Squat, eventually the tire will took all the force. If not, the suspension can absorb some. so Anti-Squat seems to have negative effect on available grip? i try to find the answer online for a long time, some say yes, some say no and i still do not get a proper answer.
The answer to this question is very complicated and not one I have seen much discussion on. I have talked to race car drivers/builders who feel that excessive anti-squat is bad. Weight transfer will happen regardless of how much anti-squat you have. It is simply a function of the wheelbase, CG height, vehicle weight and acceleration. It has absolutely nothing to do with the suspension. However, the speed at which the weight transfer happens and the speed at which the tires "see" the weight transfer is definitely a function of the suspension. With a lot of anti-squat, the tires see the effect of the weight transfer more quickly. The affect can be that the tires are suddenly hit by the weight transfer and this can upset the tires and make them loose traction. I think this is what the race drivers are talking about. With less anti-squat, the tires will see the effect of the weight transfer more slowly. I have never seen any science behind this though so this is all strictly anecdotal.
@@suspensionsexplained Thank you so much for answering me. For myself, it is harder for me to feel the limit of the tire with a car with high anti-geometry. Especially when turn in with high anti-dive geometry car. May you talk about anti roll bar in later video? will it affect grip as well? For example comparing a car with both big anti roll bar front and rear with a car with small anti roll bar front and rear.
Sir, why is that one arm in the lower wishbone is always perpendicular to the body rather than like in the upper arm where both two arms are in same angle with respect to the body
Leaf springs do make thing a bit more difficult but the main thing to remember is that with leaf springs you are talking about a live axle so the anti-squat lines go to the tire contact patch, not the wheel center. The problem is knowing exactly how the contact patch will move since the arc of the springs, the orientation of the shackles, and the location of the axle along the length of the springs all play a role in determining how the contact patch moves as the axle moves up and down. It is much more difficult to model than a suspension made up of links and control arms.
A lot of "tutorials" often depict F1 cars, which I assume have an IRS ;) They create an instant center but then draw the line from that center to the contact patch (example suspensionsecrets) -- that is incorrect then?
Thank you for taking the time to make these videos, they are much appreciated. What I rarely see mentioned is the effects of varying antisquat % on forward traction or bite on a powerful RWD car on radial tires. Do you generally want less antisquat % so as not to shock the tire, or more antisquat % to push the car forward? This of course assumed a modern, competent IRS setup without excessive camber change with bump or nasty bumpsteer. Interested to hear your thoughts on this.
@@suspensionsexplained Drag-oriented vehicles with automatic transmissions and 15" slicks, racing from a dig generally run ride rates of 1.0-1.2Hz and anti-squat percentages > 100. What would be a good ballpark for a powerful road-race (or drift) oriented RWD running 18" rubber and a ride rate in the region of 1.7-2.0Hz?
@@HydraPerformance. I'm no expert on drift cars but it seems to me you wouldn't want much anti-squat at all in a drift car since you want to be able to break the tires loose at any time. Lots of anti-squat means the tires are jammed into the ground when you apply the throttle giving them more traction instantaneously. I would recommend very little anti-squat and instead control the motion of the body with spring rate.
Hello from South Africa. How could I apply this anti squat to my Formula Vee which has trailing arms that go to rear of frame. Surely I need some a ti squat to help car come out of corners. My trailing arms are adjustable with spaces. How could I measure anti squat with my rear suspension system. Thanks in advance NB:- Have not found and suspension program that can measure that. All for wishbone type suspensions.
Trailing arms can cause big problems with anti-squat. The most famous example of this was the Triumph TR6 which had trailing arms and was pro-squat, meaning it would squat a ton during acceleration. What you need to make sure is that the trailing arm attachments to the body are located higher than the wheel center. That way the wheel center will have a rearward trajectory as it moves up. That was not the case with the TR6. The fix for the TR6 was to drill another set of holes in the body to allow the brackets holding the arm bushing to move up. I used to own one of these cars and that modification does make a big difference.
@@suspensionsexplained I have never run trailing arm higher than wheel centre. Dropped in down(remember my trailing arms go to rear of frame) . I ran them level this last meeting and in the rain we had car was terrible to drive. Will drop down again for next race meeting early October. Would have to buy longer bolts to move arms up. Will try that for last race meeting early November.Thanks for your help. Will let u know how mods helped. Are u in the UK???
0:15 wasnt sure if the video would touch on anti sway bars, because I see all these guys putting sway bars in their cars. Why would you want to install a bar that makes your car squirrelly?
There are a number of reasons for installing an anti-sway bar but anti-squat is not one of them. Sway bars, or anti-roll bars, work in cornering, not during acceleration. That's a topic for a future video.
No, the weight transfer won't increase significantly if at all by having pro squat. You'll just get other undesirable dynamic geometry changes by compressing the rear suspension, like more negetive camber (not good for acceleration) to
Wow, Ok just Wow but, I have questions; "The "anti's" are very important for a super high horse-power vehicle. How do you weight the value of anti-squat over a spectrum of vehicles say, Dragster to a truck for hauling to a 4WD off road vehicle?" How does one adjust the instant center goals for these vehicles? There are drag enthusiasts who explain what they need to race but, the concepts are never adjusted from 2000HP drag car to a 600HP 4WD truck. And AWD car has a torque distribution but, a real 4WD truck is most often only 2WD at 0% torque distribution. What are your thoughts on this? I understand how to maintain pinion angle but, that isn't the whole story. That effort must be balanced with concerns about instant center location. This is quite a balancing act. I did notice that the upper A frame of my 2500 was not parallel to the lower and I thought "WHAT". Now I see why. The A frame pair have their own instant center and if they were parallel the axis lines would never intersect. Same is true with a 4-link rear suspension. If each pair of links, upper and lower were parallel the pinion angle would be maintained over the range of travel but there would not be any projected instant center for the rear suspension. Now that I am a "wise-idiot" I'd love to know more about how to balance all this.
you explained what it is quite well - but I was expecting you to show how push rods and pull rods are changed to actually perform this function. - move this forward and you increase anti squat for example....
Great video! I would add that upper a-arms also effect jacking when they are present and in most instances override or counter the jacking effect of the lowers.
Great explanation. The piece I'm still trying to wrap my head around is how much anti-dive or anti squat or anti-roll do I want in a design? Could you do a video talking about that a bit?
If a vehicle were equipped with electric hub motors, would it be modeled as an independent suspension or a live axle? Thank you for the excellent content! You have a new subscriber
Kinda blew my mind that the slot would have more angle, not less, on a split AWD system.. I figured the AWD would squat less to start with, due to less torque being sent to the rear wheels pushing the car down. I am trying to remember if the rear suspension on my AWD E46 is different from the RWD cars, or if it was "close enough for government work" and the parts are all interchangeable. I know the springs are different (mine is on aftermarket H&Rs though) and the dampers might be as well (I have Bilsteins, and when I replaced them due to one of the rears being blown, the new recommendation from Bilstein was to use the E36 M3 dampers out back... the other design was weaker with a smaller rod).
mry82, The "anti" properties of a suspension have the function of taking horizontal forces (like from acceleration or braking) and turning them into vertical forces that counteract the weight transfer force. Since the weight transfer force is a function of the total acceleration or deceleration of the vehicle, the rear suspension in a RWD car will have more force to work with than the rear suspension of an AWD car. This is because in an AWD car, the percentage of acceleration contributed by the rear suspension is less than it would be in a RWD car. This means that the lower amount of acceleration force coming from the rear has to do more work to counteract the weight transfer which is a function of the TOTAL acceleration force.
PLEASE continue this series. You're the only person who explains not only this precisely, but who provides quantification. I'm hoping through trawling what you have created that I can find something on heave spring / 3rd element. So far, I've yet to see a good explanation. But I'd settle out of court for explanations on shocks, ideal suspension stiffness, and of course, you probably know better than I what things most people either don't understand or (worse) falsely believe they do understand. I can only imagine how busy you must be (assuming you're an ME), but you'd easily develop a channel far larger than Engineering Explained. You're just a better teacher.
I see you've done a few on braking which I think I'll watch first. I think most people misunderstand brake hardware, and assume more pistons, cross drilled, and larger radius equals greater clamping pressure, provides needed ventilation and greater leverage for stopping. If I'm not mistaken, the usual problem is adequate thermal mass in the heatsink and rate of heat removal afterwards to avoid fade ... which can be accomplished either through larger radius or via thicker rotors. In which, I'd assume a thicker rotor would be superior: Providing slightly less angular inertia / momentum. Provided the existing calipers have the clamping force to lock up the wheels at the highest top speed, ,additional pistons aren't needed. And cross drilled are just opportunities for cracks ... if any machining should be done, gas slotted is preferable. But all things being equal, the lightest caliper that provides _adequate clamping force_ for the peak angular momentum is the proper sized rotor. In order to need more clamping force, you'd either need to stop the same angular and linear momentum, or, have increased traction via grippier tires and downforce. Otherwise, most bigger brakes (especially on lighter weight cars) is a vanity purchase / cosmetic.
What I really want to learn more about / understand is bump & rebound (shocks), and how to make them work best. And of course, the aforementioned physics of heave springs and their limitations: Can it reduce only a percent? If so, what's the upper limit? Or can it eliminate an axle's squat completely ..?
I wish you were local. I'd love to work with you creating content. I honestly think you could be a "youtube star." As in ... get manufacturers offering you loaner vehicles for articles, and ultimately income. Not only do you understand your field, but you're an exceptional educator.
If you're interested ... please contact me. same username at google's mail. I think I could help with a few things: Content ideas, editing (i'm not great but I don't mind putting the work in) ... and as someone who doesn't know much, I think it's kinda difficult for people who know things to remember what it's like to not know, and to know when they've adequately explained to the weakest link's pace. I can be that weakest link. :) (so weird that more companies aren't looking for my amazing skill).
And if not, I'll just enjoy watching your content. Thank you again for your generosity of time and knowledge.
I haven't covered heave springs yet but I covered springs in general in my video on spring stiffness: ruclips.net/video/feu6-6unarM/видео.html
Really should try rewatching this whilst less sleep deprived lol
I’m there
OMG this is so enlighting, I've never seen any content that as specific like this! Thank you, sir!
Thank you for your kind words and you're welcome. There's much more to come.
Wow I haven't understood anti-squat for so long, this was an amazing explanation!
Great stuff. I didn't know about the distinction in anti-squat with IRS vs live axle, and the explanation of AWD vs RWD was also new for me. Anti-squat is something I want to look at on my BRZ. Common wisdom in the community is that it has too much because its rear suspension comes from the Impreza.
Thank you for finally shows how it actually works instead of just saying "do this to find this"!
Just stumbled onto your channel, you're doing a very good job! One thing that confused me though, if you look at Race Car Vehicle Dynamics page 631, it seems you don't find the instant center by drawing lines through the chassis mounts, but rather the continuation of the A arms untli you're laterally in the center of the wheel. I.e. with parallel wishbones, your instant center would be correct, but with the angled upper wishbone, the upper line would be offset vertically, imagining the upper wishbone to extend all the way until the tire center line, and your instant center would be a bit further to the left.
Niels, Yes, that is correct but it really only becomes an issue if the sideview angle of the arms is very severe which it rarely is. With more conventional arm angles, the error is small and can be ignored. To me, what it really points to is that the second method, which looks at the motion of the contact patch, is really the preferred method and it is what is done by all multi-body dynamic software systems that I have used. It's far more accurate and doesn't care what the suspension architecture is.
@@suspensionsexplained Thanks for your reply! I like how you present it, the sliding pin example as well. Hope you get more views in the future. There is a lot of popular superficial vehicle dynamics on youtube, often including mistakes, so it is refreshing to see your stuff.
I came her from Matt's recent video, I will definitely watch some more videos on here!
Welcome!
SuperFastMatt sent me as well
The kind of a channel that I've been looking for so long.. great videos! Thanks for your great explanation 😊
Very interesting and clear.
What about if it was a Portal axle, where the center of the axle shaft is not the center of the wheel hub?
Good question. It would certainly be different. The way to think it through is to picture the vehicle up against a wall. Apply torque from the engine and see what happens. The car can't move because of the wall so the engine just torques up the wheel. In a normal independent suspension, the wheel would try to turn but couldn't because of friction with the road. the result is that the engine torque just tries to push the suspension forward at the wheel center. With a portal axle, you still have the force pushing the wheel center forward, but there is also the gears in the hub where the gear attached to the input shaft is trying to "walk" around the gear attached to the wheel, so there is a moment being generated inside the knuckle/hub. The size of that moment also depends on the gear ratio of the portal axle and the type of gears: is it a simple two piece gear reduction or is it a planetary set, in which case the input shaft may actually spin in the opposite direction compared to the wheel. All of these factors would influence how the anti-properties would be affected by a portal axle setup. Sorry, there are never easy answers!
Boom another highly concise and informative one thanks a lot sir
I’m glad Matt recommend your channel, you explain things well.
How do the principles apply with leaf springs and traction bars on a straight axle car?
I understand the traction bar is really to keep the spring from wrapping up. Would you move the front spring eye up or down to adjust anti-squat? Also how would the regular spring shackles vs a slider at the rear of the spring affect the anti-squat.
The principles are exactly the same. Keep in mind that with a solid axle, the line needs to be drawn from the tire contact patch, not the wheel center.
WOW! Thank you, I am the only person on earth that will need to watch this twice...lol
Brilliant, clear explanation. thank you!
The Yamaha Tenere 700 utilizes anti-squat. Front wheel traction is important when riding motorcycles off-road to steer/counter-steer using throttle. Helps alleviate rear suspension from compressing and rebounding too quickly, causing a highside crash which can launch the rider clean off the bike.
it shows the advantage and shortcomings of the different suspensions in a blink of the eye
brilliant explanation for anti-squat. thank you!
Clear, simple, brilliant
we need a video on dive, and lift....good coverage
Hello! Could you please elaborate more on why the reaction point is different between live axle and independent suspension? I am doing a research, if you can please point me out if you know literature which expands on the physics behind this. thank you very much
Does this work the same way for front wheel driven cars?
Excellent explanaition, even though200/25 is not 80, 2000/25 is, so i understand what you mean! Kgm ( kilogram meter is a very good definition of torque, 1kgm=1kg, one meter from center of rotation.
What is the advantage to a geometry that squats in an independent rear suspension, rear drive car? Does it make acceleration out of a corner more controllable or predictable?
I know that a drift setup often shifts weight to the rear wheel opposite the slide. For grip racing why would any car be setup to increase squat on acceleration?
“It’s all going to come out…in the end” : That guy.
Great great video. Thank you!
hello sir can you post a series on DESIGNING A SUSPENSION GEOMETRY FOR A FSAE CAR - DOUBLE WISHBONE, DAMPER TO LOWER ARM TO BODY or PUSH ROD SUSPENSION,
I will be waiting sir
i request you sir
Do we draw the line for the perfect angle from the contact patch to the front axle / CG point regardless of where the differential is mounted?
No, the ideal line is drawn to the tire contact patch only with solid axles. With independent suspensions, the line is drawn from the wheel center. Always drawing it from the tire contact patch is the mistake many people make.
There is something that does not make sense to me. You describe 100% anti-squat as "completely cancelling out weight transfer".
My understanding of weight transfer is the reduction in normal load of the front tyres and corresponding increase in normal load of the rear tyres under acceleration, which occurs for the reason you explained at the start of the video, with the moment created by the CoG being some non-zero height above the contact patch. I can see how 100% anti-squat will mean that no compression of the rear suspension springs (and corresponding extension of the front suspension springs) will occur- the vehicle will remain completely level during acceleration. However I cannot see how this can change the normal load on the tyres themselves. If we treat the wheels and body of the car as a whole system, the free body diagram you drew at the start of the video still applies- any forces that occur within that system must cancel each other out. Alternatively, looking at the system as the body and wheels separately, if we consider your wheel with a pin moving in a slot, if the wheel pushes the body of the car up due to the angle of the slot, the body of the car must push the wheel down with an equal magnitude force. In other words, the load transfer, and therefore ultimately the normal load "felt" by the front and rear tyres has not changed whether we have anti-squat or not.
I understand that there will be a caveat to this, that the amount of anti-squat will to some extent change the motion of the CoG itself in the car's reference frame during acceleration, but I imagine the effect of this on load transfer is low.
Please let me know if I have understood this correctly and thank you in advance!
You're understanding is spot on. As you noted, the amount of weight transfer is independent of the anti properties of the suspension. It is simply a function of the mass of the vehicle, the acceleration, the CG height and the wheelbase. Nothing else. You are also correct in assuming that the motion of the body as a result of squat and lift will have some impact on the height of the CG, and therefore the weight transfer, but the effect is minimal.
Similarly, 100% anti-squat in the rear suspension also will have no impact on the weight transfer, only on the way the suspension reacts to it. But it will only impact the way the rear suspension reacts to it. It can have no effect on the front suspension since in a RWD car, the front has no acceleration forces to help counteract the weight transfer. The front will lift in response to the weight transfer no matter what is happening at the rear. Having 100% anti-squat simply means the rear suspension will not deflect in response to the weight transfer. That is all it does.
I hope this helps.
This video illustrates a solid axle real differential but that setup is omitted from the roll center video. Does anybody know of a good video about the rear roll center with a solid axle and panhard bar?
Thanks
What would be, for you, the best system to use in drag racing on tracks WITHOUT GLUE, NO PREP, that works above 100 AS or below?
I have never designed a suspension for a race car but I have talked to people who have. The general feeling I have heard from them is to keep the amount if anti properties to a minimum. That way, you can control the way the car moves with springs, dampers and anti-roll bars. If you have a lot of anti properties, and this includes high roll centers since those are in reality anti properties in cornering, reduce the amount of force traveling through the springs. This means that spring changes have less impact on the way the car handles since they have less force to work with. Think of it as a signal to noise ratio. Having as much force traveling through the springs during cornering, braking and acceleration means you have more "signal" to work with when it comes to tuning the suspension. Also, anti properties mean that the weight transfer reaches the tires sooner because you're not waiting for the body to react and move before the force builds in the tire. This may cause changes in the loading of the tire contact patch that may be too quick for the tire to handle. I can imagine a slower build-up of tire forces meaning that any over or understeer that would happen as a result of the weight transfer would happen slower and be easier to catch and manage.
I'd love to learn more about this if anyone has any thoughts or experiences with it.
Sory, i says for dragrace NO PREP
Thanks once again. What do they say? "If I knew then what I know now". (-;
I've been told that independent suspension cannot have strong enough anti-properties (particularly anti-squat) without making other responses like the roll centers and various geometry gains far less than ideal. Is this the case, and if not, which independent suspension designs are there that can be used both front and rear that allow you to independently control as many responses as possible?
The instant centers are independent of other properties like camber gain, toe change, or roll center height because those are properties that happen in the other dimensions. i.e., camber change happens in the rear view, toe change happens in the top view while the anti properties happen on the side view. Since they are effectively orthogonal to each other, you can independently control them to a large extent There are limits of course, but they are at the extremes. Most independent suspension designs give you the ability to control these factors independently.
@@suspensionsexplained How much anti-squat do you think a designer should go with in a street driven performance car? I've read that you don't want 100% because then the driver doesn't feel right when the car accelerates, but at the same time, it's demonstrably better to have some anti-squat for forward acceleration. Also, over 100% can do weird and messed up things, correct?
All that aside, I also just watched your video on anti-dive and lift... Is it better to prioritize high anti-lift even if you DO end up getting weird 100% or more anti-squat, or should you get your anti-squat correct and then just accept whatever anti-lift that gives you? Also, is the instantaneous radius method also better for anti-squat calculations, or is the geometric method typically more viable here than it is for anti-dive/lift?
Congratulations on recognising this. Squat and dive are simply positive and negative pitch. The pitch centre is found in side view in exactly the same way as the roll centre is found in cross section.
Yes and no. The roll center is always found with lines drawn to the tire contact patch. My point here is that for anti-squat, you sometimes need to go to the contact patch and sometimes to the wheel center, depending on your suspension and brake system architecture. Too many people seem to think you always go to the contact patch and that is not correct, as I described.
Hi Hubert,
Thank a lot for your video I finally understood why force would apply at CP on a live axle. 👍
I have one for you:
If the car you draw @6:20 is a RWD with a live rear axle, it would have 100% anti squat. So no squat on power, right?
Now if you draw the Side View Instant Center of the front suspension, the intersection of front and rear SW IC will be the pitch centre, right?
It is totally possible that your pitch centre locates way below the Suspended Mass CoG...
So then if you have a pitch moment, how can you not have squat?🤔
The way I feel it, is that anti effect work according to this definition only if one axle is connected...
Laurent
Laurent, The front suspension IC would only be relevant if there is also drive torque going through the front. But in a RWD car, all the drive torque is going through the rear so there are no forces being applied on the front to help counteract the lift that happens on the front during acceleration due to the weight transfer. That is why on a RWD car, the ideal line does not go through the CG but instead goes through a point at the height of the CG above the front wheel centerline. Remember, the pitch moment comes from a horizontal force acting at the height of the CG. It doesn't care where the CG is longitudinally. It only cares about its height above ground.
@@suspensionsexplained Hubert, I agree but that's not my point.
Let's take this example:
Say you design a RWD car with 100% anti squat.
Make it accelerate from a stop at 1G
Will it squat? supposedly No.....
Design the front suspension so that the Pitch axis is well below the SM_cg.
Now you have a car with 100% anti squat but also a consequent pitch moment arm.
Make it accelerate from a stop at 1G
Will it squat?
No it will not squat, but the front will lift. "Anti" properties (anti-lift, anti-squat, anti-dive) work because they take the horizontal forces (from acceleration or braking) and convert them into vertical forces which counteract the forces from weight transfer. So, if there are no horizontal forces then there cannot be any "anti" forces. What this means is for a RWD car, the front suspension design has no impact on the amount of squat that happens in the rear. All the front suspension does is react to the weight transfer since there are no horizontal forces to counteract it. This means the IC of the front suspension or where it crosses the IC line of the rear suspension is irrelevant. It doesn't matter if this intersection is below the CG or not. All that matters is where the IC line from the rear goes since that is the only place where acceleration forces are coming from.
@@suspensionsexplained Hubert, thank you for your explanations!
But what does the pitch axis do then? Maybe you need to make a new video...😉
The pitch axis is relevant during braking because there are forces coming from both the front and rear suspensions. It can also be relevant during acceleration in an AWD situation but then the lines need to be drawn correctly considering which suspension is a live axle and which one is independent.
I'm in Albuquerque, can I have a anti -theft suspension , please.
Sure, move to Idaho.
It's called a manual transmission!
Thank you for your video, i do have a question, would Anti-Squat affect grip or not? if yes/no, how and why?
by common sense, it seems that if there is Anti-Squat, eventually the tire will took all the force. If not, the suspension can absorb some. so Anti-Squat seems to have negative effect on available grip?
i try to find the answer online for a long time, some say yes, some say no and i still do not get a proper answer.
just to clarify, i am talking about mechanical grip, aero is not considered
The answer to this question is very complicated and not one I have seen much discussion on. I have talked to race car drivers/builders who feel that excessive anti-squat is bad.
Weight transfer will happen regardless of how much anti-squat you have. It is simply a function of the wheelbase, CG height, vehicle weight and acceleration. It has absolutely nothing to do with the suspension. However, the speed at which the weight transfer happens and the speed at which the tires "see" the weight transfer is definitely a function of the suspension. With a lot of anti-squat, the tires see the effect of the weight transfer more quickly. The affect can be that the tires are suddenly hit by the weight transfer and this can upset the tires and make them loose traction. I think this is what the race drivers are talking about. With less anti-squat, the tires will see the effect of the weight transfer more slowly. I have never seen any science behind this though so this is all strictly anecdotal.
@@suspensionsexplained Thank you so much for answering me. For myself, it is harder for me to feel the limit of the tire with a car with high anti-geometry. Especially when turn in with high anti-dive geometry car.
May you talk about anti roll bar in later video? will it affect grip as well?
For example comparing a car with both big anti roll bar front and rear with a car with small anti roll bar front and rear.
Subscribed
So, does it actually reduce load transfer?
Mbac i pil da minc
Sloppy explanation. Have no idea what he's talking about.
Sir, why is that one arm in the lower wishbone is always perpendicular to the body rather than like in the upper arm where both two arms are in same angle with respect to the body
Having a leaf spring rear wheel drive vehicle makes this video more than confusing
Leaf springs do make thing a bit more difficult but the main thing to remember is that with leaf springs you are talking about a live axle so the anti-squat lines go to the tire contact patch, not the wheel center. The problem is knowing exactly how the contact patch will move since the arc of the springs, the orientation of the shackles, and the location of the axle along the length of the springs all play a role in determining how the contact patch moves as the axle moves up and down. It is much more difficult to model than a suspension made up of links and control arms.
A lot of "tutorials" often depict F1 cars, which I assume have an IRS ;) They create an instant center but then draw the line from that center to the contact patch (example suspensionsecrets) -- that is incorrect then?
Yes, that is incorrect. With an IRS, the line is drawn from the wheel center, not the tire contact patch.
Thank you for taking the time to make these videos, they are much appreciated. What I rarely see mentioned is the effects of varying antisquat % on forward traction or bite on a powerful RWD car on radial tires. Do you generally want less antisquat % so as not to shock the tire, or more antisquat % to push the car forward? This of course assumed a modern, competent IRS setup without excessive camber change with bump or nasty bumpsteer. Interested to hear your thoughts on this.
It's a balancing act. A bit of anti-squat does help push the tire into the pavement initially, but too much will "shock" the tire.
@@suspensionsexplained Drag-oriented vehicles with automatic transmissions and 15" slicks, racing from a dig generally run ride rates of 1.0-1.2Hz and anti-squat percentages > 100. What would be a good ballpark for a powerful road-race (or drift) oriented RWD running 18" rubber and a ride rate in the region of 1.7-2.0Hz?
@@HydraPerformance. I'm no expert on drift cars but it seems to me you wouldn't want much anti-squat at all in a drift car since you want to be able to break the tires loose at any time. Lots of anti-squat means the tires are jammed into the ground when you apply the throttle giving them more traction instantaneously. I would recommend very little anti-squat and instead control the motion of the body with spring rate.
Hello from South Africa. How could I apply this anti squat to my Formula Vee which has trailing arms that go to rear of frame. Surely I need some a ti squat to help car come out of corners. My trailing arms are adjustable with spaces. How could I measure anti squat with my rear suspension system. Thanks in advance NB:- Have not found and suspension program that can measure that. All for wishbone type suspensions.
Trailing arms can cause big problems with anti-squat. The most famous example of this was the Triumph TR6 which had trailing arms and was pro-squat, meaning it would squat a ton during acceleration. What you need to make sure is that the trailing arm attachments to the body are located higher than the wheel center. That way the wheel center will have a rearward trajectory as it moves up. That was not the case with the TR6. The fix for the TR6 was to drill another set of holes in the body to allow the brackets holding the arm bushing to move up. I used to own one of these cars and that modification does make a big difference.
@@suspensionsexplained I have never run trailing arm higher than wheel centre. Dropped in down(remember my trailing arms go to rear of frame) . I ran them level this last meeting and in the rain we had car was terrible to drive. Will drop down again for next race meeting early October. Would have to buy longer bolts to move arms up. Will try that for last race meeting early November.Thanks for your help. Will let u know how mods helped. Are u in the UK???
No, I'm in California.
Brilliant, clear explanation, clear pronunciation, very enjoyable! Thanks!
Built this into my V8 trike. 400 hp in a 1,200 lbs vehicle.
Ai has gone too far
god damn , so i basically designed everything wrong but the car is already built .... also , can u be my dad ? :)
I'd love to be your dad, but you'll have to get past your would-be siblings first. The interview process is hell!!
0:15 wasnt sure if the video would touch on anti sway bars, because I see all these guys putting sway bars in their cars.
Why would you want to install a bar that makes your car squirrelly?
There are a number of reasons for installing an anti-sway bar but anti-squat is not one of them. Sway bars, or anti-roll bars, work in cornering, not during acceleration.
That's a topic for a future video.
If you are in a rear wheel drive would pro-squat not be desirable to get you more traction on the rear wheels?
No, the weight transfer won't increase significantly if at all by having pro squat. You'll just get other undesirable dynamic geometry changes by compressing the rear suspension, like more negetive camber (not good for acceleration) to
Great content.
Wow, Ok just Wow but, I have questions; "The "anti's" are very important for a super high horse-power vehicle. How do you weight the value of anti-squat over a spectrum of vehicles say, Dragster to a truck for hauling to a 4WD off road vehicle?" How does one adjust the instant center goals for these vehicles? There are drag enthusiasts who explain what they need to race but, the concepts are never adjusted from 2000HP drag car to a 600HP 4WD truck. And AWD car has a torque distribution but, a real 4WD truck is most often only 2WD at 0% torque distribution. What are your thoughts on this? I understand how to maintain pinion angle but, that isn't the whole story. That effort must be balanced with concerns about instant center location. This is quite a balancing act. I did notice that the upper A frame of my 2500 was not parallel to the lower and I thought "WHAT". Now I see why. The A frame pair have their own instant center and if they were parallel the axis lines would never intersect. Same is true with a 4-link rear suspension. If each pair of links, upper and lower were parallel the pinion angle would be maintained over the range of travel but there would not be any projected instant center for the rear suspension. Now that I am a "wise-idiot" I'd love to know more about how to balance all this.
you explained what it is quite well - but I was expecting you to show how push rods and pull rods are changed to actually perform this function. - move this forward and you increase anti squat for example....
Really good stuff! I wonder how thiis affects ghe job of the dampener/shock absorber? Do you want anti squat if the track is uneven?
Great video! I would add that upper a-arms also effect jacking when they are present and in most instances override or counter the jacking effect of the lowers.
You make me immediately want to go back to college, if you don't teach professionally you certainly should
Great explanation. The piece I'm still trying to wrap my head around is how much anti-dive or anti squat or anti-roll do I want in a design? Could you do a video talking about that a bit?
For more on anti-dive, including some target numbers, see my video here: ruclips.net/video/HeclLbsRHbc/видео.html
New subscriber! Nice explanation!
You explain this well. Do you teach at a school?
If a vehicle were equipped with electric hub motors, would it be modeled as an independent suspension or a live axle? Thank you for the excellent content! You have a new subscriber
Or would need modeled as a live axle because the torque reaction is going through the suspension.
Kinda blew my mind that the slot would have more angle, not less, on a split AWD system.. I figured the AWD would squat less to start with, due to less torque being sent to the rear wheels pushing the car down. I am trying to remember if the rear suspension on my AWD E46 is different from the RWD cars, or if it was "close enough for government work" and the parts are all interchangeable. I know the springs are different (mine is on aftermarket H&Rs though) and the dampers might be as well (I have Bilsteins, and when I replaced them due to one of the rears being blown, the new recommendation from Bilstein was to use the E36 M3 dampers out back... the other design was weaker with a smaller rod).
mry82, The "anti" properties of a suspension have the function of taking horizontal forces (like from acceleration or braking) and turning them into vertical forces that counteract the weight transfer force. Since the weight transfer force is a function of the total acceleration or deceleration of the vehicle, the rear suspension in a RWD car will have more force to work with than the rear suspension of an AWD car. This is because in an AWD car, the percentage of acceleration contributed by the rear suspension is less than it would be in a RWD car. This means that the lower amount of acceleration force coming from the rear has to do more work to counteract the weight transfer which is a function of the TOTAL acceleration force.
Thanks for that clear, concise explanation! Looking forward to more videos. @@suspensionsexplained
Matt Brown sent me! Glad I found your channel. If I may make a request: could you do a video discussing preload and how it effects ride comfort?
Thanks for the suggestion. This will be part of a larger bushing topic that I will cover in the future.
@@suspensionsexplained Thank you. Looking forward to it