Toe out for turn in

[raymondu999]

I've just re-watched 2011 Monaco FP3 (yes, I'm sad. Blame it on F1 withdrawal symptoms) and Anthony Davidson says Toe In gives better turn in, makes it a more twitchy car; while toe out makes it more "lazy" on turn in.

[Jersey Tom]

It's all in how you interpret what the car is doing. Two different people can describe things very differently.

Toe-in can certainly make a car feel more lively, as I believe we've discussed earlier.

[raymondu999]

I think I'll just stop posting in this thread and shut up. All of this is confusing me! Makes the mind boggle how you tyre engineers work, JT

[marcush.]

it´s like everything -more and less can have almost similar effects depending on where your starting point is,the magnitude of change you create with your adjustment and of course if the car is even sensitive to the ajustment .
think of installation stiffness and a adjustment for toe in could well move to toe out or even more toe in under braking or acceleration or bump or simply deflection of frame or suspension components.
The moment you are not taking everything important into account the reactions on adjustments can easily surprise you.

[machin]

think of installation stiffness and a adjustment for toe in could well move to toe out or even more toe in under braking or acceleration or bump or simply deflection of frame or suspension components

I was kind of hoping that we would all be assuming that deflection of suspension bushes etc wouldn't be taken into account when discussing this thread, because, like you say, it complicates things somewhat... and anyway, a rear wheel drive car would generally try to "toe-out" when subjected to acceleration or braking, which is why to eliminate scrub the general rule (oops, there's another one!) for rear wheel drive cars is to have a little bit of toe-in.....

if the end result is some understeer, then the transient turn in behavior will feel more aggressive.

What's the mechanism that causes this? In traditional control theory if you increase the rate of response then the system becomes less stable, and vice versa... this would suggest that increasing the turn-in rate would lead to a more oversteery car...?

[Jersey Tom]

Front toe out doesn't increase the 'P' gain - it decreases it. Effectively you help dampen the system in yaw. End result is you should get to a settled condition more quickly and with more "precision" which IMO can be a plus.

Toe in front on the other hand should increase the 'P' gain for yaw/steering. If you are already very damped as it is and the car feels numb to steering input, this can also be advantageous.

Depends which side of the fence you're on. To that note, per RCVD's basic derivation the yaw damping is inversely proportional to speed (or the square of speed, don't have it handy) so a lot of this becomes contingent on what type of corner you're attacking, as well as how much downforce is available, type of tire, etc.

[Smokes]

JT does the model take into effect that in a straight line the front wheels want to toe out due tyre wall slip and flexural stiffness of the wheel and play in the linakage. When racing R/C cars you see issue like this due to materials used and wear an tear. I find front toe out seems to car have more turn in but makes the car turn argressivly, and toe in make the car understeer but it turn more lazy.
Plase note the servos can go from 0 to 60 degrees in 0.3s we tend to have to slow the turn rate through transmitter programing.

I am not sure what you think of this http://users.telenet.be/elvo/for r/c car handling.

[marcush.]

from a toe out straight ahead driving into a corner the loading of the tyre has to go through a change of load direction ,it´s a bit like a window wiper .If you are already preloading it in toe in it´s a progressive loading of the tyre if it´s in toe out you will feel a delay and then a more severe rise in loading of tire which may be interpreted as aggressiveness or responsiveness.

[Jersey Tom]

JT does the model take into effect that in a straight line the front wheels want to toe out due tyre wall slip and flexural stiffness of the wheel and play in the linakage. When racing R/C cars you see issue like this due to materials used and wear an tear. I find front toe out seems to car have more turn in but makes the car turn argressivly, and toe in make the car understeer but it turn more lazy.
Plase note the servos can go from 0 to 60 degrees in 0.3s we tend to have to slow the turn rate through transmitter programing.

I am not sure what you think of this http://users.telenet.be/elvo/for r/c car handling.

R/C cars use foam, non-pneumatic tires with no actual composite structure to them no? Completely different.

As for wanting to toe-out on a straight line... not sure I agree with that. Don't get slip angle confused, it's taken as the orientation of the WHEEL to travel direction. Don't get mixed up with sidewall deflection and whatever. Straight line there should be almost no compliance and linkage "slop" should be almost non-existent on any decent car.

[machin]

Straight line there should be almost no compliance and linkage "slop" should be almost non-existent on any decent car.

I highlight the word "decent" in your reply -a lot of us dabble with road cars where rubber suspension bushes are prevalent; here the turning moment caused by the drag from the wheel tends to cause the front wheels to point outwards when accelerating or braking (for rear wheel drive cars), or point in on acceleration and out on braking (front wheel drive cars)....

[Jersey Tom]

Even with a road car, bushings are a compliance rate rather than outright slop. Former is inevitable, latter is inexcusable.

[machin]

Exactly; its that compliance rate which we have to take into account when setting up our real cars...

But theoretically I'd assume that the bushes are perfect ; pure rotation in the desired directions and nothing more.

I'm starting to agree with one of your earlier posts; it depends how you define 'better turn in'... In my definition (achieve a desired turn rate quicker after starting to apply steering action) it doesn't seem to be improved by toe out at all... I think that's your conclusion right?

[Jersey Tom]

I'm starting to agree with one of your earlier posts; it depends how you define 'better turn in'... In my definition (achieve a desired turn rate quicker after starting to apply steering action) it doesn't seem to be improved by toe out at all... I think that's your conclusion right?

Even then by "quicker" do you mean a higher gain of yaw moment control, then leading to a higher initial yaw acceleration... or do you mean time for the system to reach equilibrium again after an input action.

[Smokes]

JT does the model take into effect that in a straight line the front wheels want to toe out due tyre wall slip and flexural stiffness of the wheel and play in the linakage. When racing R/C cars you see issue like this due to materials used and wear an tear. I find front toe out seems to car have more turn in but makes the car turn argressivly, and toe in make the car understeer but it turn more lazy.
Plase note the servos can go from 0 to 60 degrees in 0.3s we tend to have to slow the turn rate through transmitter programing.

I am not sure what you think of this http://users.telenet.be/elvo/for r/c car handling.

R/C cars use foam, non-pneumatic tires with no actual composite structure to them no? Completely different.

As for wanting to toe-out on a straight line... not sure I agree with that. Don't get slip angle confused, it's taken as the orientation of the WHEEL to travel direction. Don't get mixed up with sidewall deflection and whatever. Straight line there should be almost no compliance and linkage "slop" should be almost non-existent on any decent car.

Rubber with a foam insert for off road an touring cars foam insert controls the air gap between the rimm and the tyre a bit like changing tyre pressure. foam tyre are used in some classes but they have a stick slip behavior as they rubber foam is able slip at various angle due the air pockets in it which means they can pull 6g or 7g.

With regard to compliances Road car rubber bushes are far from perfect, shore tolerances for production is +- 5. The also perish a different rates due to heat exposure age and wear and tear. I just replaced rear supension bushes in 9 year old M3 that has done 52000 miles. The bushes had distringrated, they are usally designed for 100,000 miles or 10 years for prodution road cars.

[Ian P.]

It was about 20 years ago that I read Carroll Smith's "Tune To Win".

https://www.pegasusautoracing.com/group ... pID=CSMITH

He has a very specific and quite detailed section on setting up toe in/out for both ends of the car as well as recommending tweaking the Ackerman geometry of the front steering.
All of this was about affecting turn-in, stability and response of the rear of the car to steering inlut.
Naturally I was skeptical but had the opportunity to try it on a dune buggy and a couple of cars since. It all works exactly as he predicted. Front and back.
Toe out at the front (increasing Ackerman angle) gives more steering effect for the same steering wheel input.
Toe in at the rear does the opposite but for different reasons.
If you just do some simple geometry and sketching on a piece of paper, it pops out that the moment arm for the inside front wheel can be considerably more effective at turning a car, especially a front engined car, than the outside wheel. Take an Austin mini with loads of steering input, the lateral force vector of the outside wheel will come close to intersecting the CG, hence, no turning effect. Even though the inside wheel is only lightly loaded, this is where the turning moment comes from.
Keeping both front wheels on the ground is critical for most cars (especially F1 cars). The classic Porsche picture with the inside wheel up in the air is a different story, mostly because the CG is so far aft, the outside front wheel has loads of moment arm to act through to turn the car. Then you can reduce the rear roll stiffness to keep both rear wheels on the track and the car can still go round corners. Back to the paper and geometry exercise, where all is revealed.