Is 50/50 Weight Distribution the best for GRIP?
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- Опубликовано: 30 июл 2024
- What is the best Weight Distribution for a car? Is it 50/50, or is that what auto manufacturer's want you to believe? Let's look under the 'hood' and see the physics of how front or rear bias weight distribution affects grip during steady state cornering, braking, and acceleration.
Topics covered:
00:00 Cars…
00:17 What is Weight Distribution?
01:02 Where is the Center of Gravity?
01:33 What is a moment?
02:06 Why is 50/50 good?
02:33 What happens to Grip when it's not 50/50?
03:34 Why are fast cars not 50/50?
04:10 When is Rear-Bias better than 50/50?
05:35 Is 50/50 ideal?
05:53 What you've been waiting for every video...
What happens to GRIP when a tire has more weight? Watch this: • How does WEIGHT affect...
Don't know why LOAD TRANSFER reduces grip? Watch this: • 4 setup changes to Imp...
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I study physics and I could never find a video giving an actual scientific explanation for this, but you have done so here and I really appreciate this
You've come to the right place!! ☺
Your explanition video's are very, very good. I hope you will make many more of these, coupled with driving techniques and setup guides. I am impressed.
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It is also a lot easier to fit wide tires in the back of a typical car than the front so it makes sense to put more weight in the back to make it easier to balance grip out. Very wide front tires can also numb the steering feel more so than wider rear tires so there are some additional benefits in handling and feel.
Great video! Love all the animations and stuff too! 👍👍👍
Thanks a bunch!
Great video
simple straight to the point .. got a sub from me
Thanks for subbing!
The weight transfer is depending on the height of the center of gravity and suspension (springs and shocks).
Actually the suspension is not a factor in how much total weight transfer occurs. May be this can help: ruclips.net/video/g6UWye-StcU/видео.html.
Do different types of races have different ideal weight biases? Ex: Would a downhill mountain race benefit a slight front weight bias in a low power FR car? or does AWD rally have a different ideal balance vs AWD track race because of the differing styles of driving?
It 'kind of' does. Going downhill, weight will be shifted forward, so you probably want to start with more rear bias in a rwd car. That said, you can make whatever platform 'work' to some extend, through wheel/suspension choices; just look at the 911.
As for AWD, my thought process would be to consider what the torque split will be, then think about what dynamic loads you want on each tire. That said, it's a bit backwards because it's easier to change the torque split than to change the weight distribution. Also, I haven't really looked into the physics of loose surfaces much so there may be factors I have not considered
togue?
Funny ending :D
Thanks!
This is sort of an observation and a question at the same time... Do RWD cars oversteer on throttle because the driven axle is behind the CoG? Conversely, FWD understeer because the driven axle is in front of the CoG? If you were to have a completely wonky setup where the CoG is somehow on the driven axle, what would happen under heavy throttle? Thanks :)
That's a great thought experiment. This video may help shed some light for you: "Why Load Transfer reduces Grip in corners [HOW TO GET MORE GRIP]" ruclips.net/video/g6UWye-StcU/видео.html.
If the CG was above the rear axle, it would mean the car could be balanced exactly on the rear axle, which would suggest the front axle would have no weight. Under any acceleration, the front will lift off the ground. In fact, any disturbance of an equilibrium would likely topple the car backwards. A real life proxy would be top fuel dragsters. They have a lot of their weight at the back (~80% I think?), right where they need it, and I'm sure you've seen what happens they launch.
So to answer your question, there are many factors that go into whether a car under or over steers. The drive wheel location (and in relation to the CG) is certainly one of them, and what you queried is one way to think about it. But in practice it would be inaccurate to suggest a car under/oversteers solely because of where it's drive wheels are. For example, a RWD car can be made to understeer on throttle, whilst a FWD can be made to oversteer. Similarly, AWD cars don't necessarily have neutral balance.
Yes. This is why rwd cars often come with offset tires. Putting bigger tires in the rear helps with the oversteer and makes the car less likely to fishtail. This giy has left out a lot of factors for strret cars. He left out a lot of the new tech that has made adding weight to the rear irrelevant. We dont drive f1 cars. He tried to use f1 cars to help explain this and that was odd. A f1 can have up to 5gs of downforce so they have thousands of lbs of force pushing them down probably 10 times the force of a street car. Any lack of weight on the rear can be fixed with proper geometry and physics. You can’t really do that with a street car. A street car can’t gas it to instantly add a 1000 lbs of downforce to the rear. With even most sports cars being closer to 50/50 is ideal unless you have a track car. This is why bmws are so fun to drive they understand this. The can make a giant suv that drives like a sports car and I promise you that 50/50 weight distribution plays an important role. He talked about fastest cars in a straight like now let’s have him mention the faster mass produced cars on a track. I bet they are closer to 50/50 🤔
Telsa came out and started making others panic. Things became less about handling and more about acceleration. So makers are making more 60/40 cars and 50/50 has become less of a goal because they want to have good 0-60
Question…. Ignoring engine placement bcs “electric motors” what’s the BEST weight distribution for an Awd long wheelbase coup in a hard acceleration situation like pro drag status?
Wow, that's an very unique question. I'll start by saying I don't know much about pro dragsters, but I'll take a stab at it. Since all 4 wheels are being driven, you want maximum grip on all 4 tires, which implies the load needs to be as evenly loaded as possible. Since during acceleration, load shifts rearward, a static front weight bias would result in even load distribution during acceleration. You'll want to find the front weight bias that results in 50/50 during max longitudinal acceleration, as that's when grip is most needed, and the long wheel base will reduce the amount of longitudinal load transfer.
However, that's holds true under the premise that all 4 motors, wheels, and tires are the same, and of course they don't have to be. If different wheels/tires are used for different axles, you're gonna start needing the tire model in order to figure out what load distribution provides the maximum total grip. Same goes for different motors. The axle with more torquey motors is going to need more grip.
There are numerous combinations you can play with. For example, having a static 50/50 weight distribution, but putting stronger motors on the rear axle to take advantage of the higher grip from rearward load transfer during acceleration. Sounds like you have a fun project your hands!
@@LastTenth …. THANKS a real answer 😎 I appreciate taking the time… since we’re invested in the topic, it is a single motor mid mount driven platform. placement of the rest of the components will determine final weight distribution. The vehicle can and will hold 1G of constant force under load up until near max speed where stability is still needed when coasting and stopping.
I know I’ll have to figure out some elements of geometry to find other points and angles that I’ll need to know to solve more formulas to find what I need to know. I also know that weight placement shouldn’t always be at the lowest center of gravity, sometimes we need to add weight higher up to achieve Weight transfer goals. In a perfect world…, If we know the vehicle will maintain one GeForce consistently for five seconds on an all-wheel-drive platform, are we looking at 60 in the front 40 in the rear? I know there are just way too many variables with tons of configurations to consider lol I just can’t help to pick your brain.
No problem at all. It's hard to say what the number you need is, whether it's 60/40, or 55/45, or other. I am no design engineer, but this is how I would approach it. First, determine the tire sizes and it's characteristics. Then you'll have to determine how much load you want on each axle to maximize longitudinal grip, from there determine how much load will transfer based on your dimensions (or vice versa), then the static weight distribution. Throughout this process I'm sure (re)iteration is required in order to satisfy practicalities like where to put what, chassis stresses, etc. But one thing to consider is that, the longer the wheel base, the higher up the CoG can be, as far as load transfer goes. Also, the less the load transfer and the more evenly loaded the axles, the more likely it will be easier (safer) to stop the car.
If the tyres are a different size though, such that the area of the front and rear contact patches were proportional to the weight biases, would this make for the same grip per weight ratio at the front and rear?
The patch size is more to do with load and tire pressure than tire size. Given same tire pressure, the heavier axle is going to have a larger patch. That said, the heavier axle generally should be running higher tire pressures to keep ride frequencies in check.
But to answer your question, more patch size would offer more grip on that axle, all else equal (which I'm not sure is possible). Moreover, anything and everything would affect the front/rear grip ratio; roll stiffness, suspension geometry, alignment, downforce, the list goes on... It's no coincidence that a 911 has much wider rear tires and a more sophisticated rear suspension than the front.
@@LastTenth firstly, thank you for getting back to me.
To double check, it sounds like then, all else being equal, the grip to weight ratio of the contact patch can be the same for both front and rear despite an unequal longitudinal (static) load? Which as you point out, the much wider rear tyres on the 911 hint towards that being likely the case?
You're welcome@@DrR1pper . In practice, all else won't be equal. With different loads, you can have the same patch size but different pressures, or if the pressures are the same, the patch sizes won't be. Even if the pressures were the same, the heavier axle will have less grip simply because of tire load sensitivity (ruclips.net/video/g6UWye-StcU/видео.htmlsi=ixo8V-WFUZH_mN3-)
@@LastTenth sorry to bring this thread back up but something is not clicking for me and I was hoping you might be able to pinpoint it out for me please.
So, if you make the rear tires larger than the front tires so that with the respectively different tire pressures for each (so that the front and rear tires have matching ride frequency) it produces a proportionally larger contact patch on the rear than the fronts (in the same proportion as the longitudinal weight distribution).....would this not produce the same levels of grip per unit weight on the rears vs fronts? The contact patch pressures would be the same for both front and rear tires. Intuitively that seems like that should therefore produce the same levels of grip per unit weight/load for both ends but I have a feeling you'd tell me my intuition is wrong here but I'm struggling to see why. Surely, tire load sensitivity must not only care about the level of normal load placed on the contact patch but also the size of the contact patch?
Many thanks in advance.
No problem@@DrR1pper. In a non-50/50 car, if the tires pressures are adjusted so that the ride frequencies are the same (ignoring springs for a moment), there's no telling whether their (static) contact patches can be proportional to their axle weight or not - that depends on the tires construction and 'spring' rate at different pressures. The heavier axle will by definition have higher tire pressures and most likely have a larger contact patch, and very unlikely will it be larger in proportion to it's weight.
If the axles somehow end up having contact patches in proportion to their weight, then I suppose the 'grip' per unit weight would be the same, given all else equal.
Theoretically, If I wanted to dive into 4 consecutive 35-45 deg.(approx.) linked turns going above 90mph with a vehicle of about 2700 lbs. rwd, what would be the best weight distribution in this scenario?
Can't really answer that; it depends on a LOT of other things things. Moreover, weight distribution is not a tuning tool. It's not generally something you can change, and when you can, it's rarely the goal.
Of course you can change it. Bmw has some this with the 3 series changing rather minor things. Also with newer tech there is no reason to have a 60/40 car is we are talking street cars. Beging up F1 cars makes no sense at all they dont relate to street cars at all. In fact if we tried to drive a f- car on the streets we could not turn the car safely and it will have very little traction. Your vidoe doest talk about downforce f1 cars must ha to handle well. Downforce also changes what the perfect weight distribution is and this is downforce street cars will never have.
Do you lose downforce when going up a hill ?
you may, depending on how the slope affects your rake, and how that rake change affects your aero.
Ok definitely moving the battery to the trunk
Yeah that's a common mod. Or at the very least, a lighter battery.
How about equally weight more towards the center like rally cars? Rally cars drivers literally are set on the middle of the vehicle.
I'm not sure what you mean by the drivers are set on the middle. More of the weight in the middle reduces moment of inertia, which makes it easier to rotate. I'm not sure rally car's fit that description since the engines are usually in the front, probably because of their production car requirements. I would expect formula cars to have the lowest moment of inertia, and among street cars it would probably be exotics.
@LastTenth OK, so I've noticed rally car builds that seats are moved more towards the center of the car, making the pilot and Co pilot sit at the center of the car Yes, the engine still at the front, but other components are moved to the rear such cooling components. For example, I drive a fw hatchback 400hp to the wheels as my commuter, no back seats. I've placed my spare tire right in the center of the car now that back seats are gone. Steering feels heavier now and corners very well 👌🏽 even when switching lanes, the steering is minimal.
@@lest187 That's pretty typical for any production car conversion, especially to get weight off the front of a front engine car. For example, one of the first things people do is move the battery to the back when converting to a race car. There maybe more reasons why they do it in a rally car because it's quite a bit of work to move the driver.