Toe out for turn in

[Jersey Tom]

If its simple dynamics, why not let us in on the secret and we can all move on to try and work out solutions to some of the world's much bigger problems....?

I've been trying to. I've already said how to do it, even the area to look at.. shouldn't take an hour or two.

How are we going to solve the world's much bigger problems if we don't even take the time to understand the fundamentals?

[thisisatest]

i'm going to take a stab at this one, as it's been bothering me for years but i never actually found an answer. i have a theory:
i actually do think it has to do with the inside tire dragging the car into rotation. i also think that, with kingpin centerlines lying inboard of tires, the inside tire lowers (into the ground) and the outside tire rises slightly, so before the car body starts rolling, the inside tire is more heavily weighted (for an instant).
also, as often is said that toe out helps with turn in, it is also said that too much toe out can lead to understeer. i think this is part of the picture. if the end result is some understeer, then the transient turn in behavior will feel more aggressive.

am i on the right track? not even close?

[strad]

Speed runs a show about NASCAR Performance that had a couple of segments on caster/camber and toe in/out.
Very basic. It's aimed a people who know very little about these things. But hidden in there is the gist of how toe and camber can affect turn in etc.
And yes toe out can help turn in..didn't know it myself til recently. I hope this helps some...I know they only turn left, but think of it as the first turn on the old Hockenheim
click photos for video

.

[machin]

If its simple dynamics, why not let us in on the secret and we can all move on to try and work out solutions to some of the world's much bigger problems....?

I've been trying to. I've already said how to do it, even the area to look at.. shouldn't take an hour or two.

How are we going to solve the world's much bigger problems if we don't even take the time to understand the fundamentals?

The world certainly has bigger problems than the fundamentals of vehicle dynamics,

I just passed on the explanation in the most recent issue of Racecar Engineering. If you're keen to prove it wrong, then please be everyone's guest, as I said before; I'm more than willing to listen to an inciteful answer....

(Strad, I'll take a look at those videos when I'm home -blocked by my work's firewall, Cheers).

[Jersey Tom]

Oh I've already proven it out to myself conceptually and through a number of sim runs. Doesn't particularly bother me what anyone else chooses to believe, be it handwavy explanations passed around here and there. It's a bit disappointing no one else has been willing to take the time to do a dynamic sim to more rigorously prove or disprove the true behavior for themselves. That's the only way to really learn this stuff IMO.

What people choose to do, and whether they want to further their understanding of vehicle dynamics is up to them. I'm all for pointing in the right direction, but not going to spoon feed answers.

[The Thorn]

So, if you know that your theory is the right one, and the rest of the world believes that the other is right, what does it say about you?
I don't mean to be harmfull to your status, but I have never seen anybody, even racing engineers, going against the thing that front toe-out gives better reaction of the front tyres.

And why, if you are so sure about your case, wouldn't you show it to us? Only thing I can think about is that you just don't have any, and post here to make other people angry with your cocky appearance.

People can tell me anything, but if they don't come up with proof, I am not even willing to believe them.

[Jersey Tom]

I'm not saying front toe out can't improve entry feel. Just saying the rationale that's being put behind it isn't correct.. and some of the subjective feel descriptions may not be entirely accurate either. For that matter you'd be surprised how many drivers and engineers aren't on the same page with terms as deceivingly simple as "grip."

The dynamics of this are simple to show. I've explained how, and even what to look for. No one has done the work! Whether or not people want to learn dynamics and investigate things rigorously on their own is no bother to me. All I care about is improving myself and winning on Sundays.

[marcush.]

I'm not saying front toe out can't improve entry feel. Just saying the rationale that's being put behind it isn't correct.. and some of the subjective feel descriptions may not be entirely accurate either.

It's simple to show. I've explained how. Whether or not people want to learn dynamics and investigate things rigorously on their own is no bother to me. All I care about is improving myself and winning on Sundays.

that´s the point it gives a certain feel to the driver .For lap time it´s not important if your driver does not need that feel for his confidence.When you are able to show him the speed he´s gaining by not dragging the fronts on the straights he´s more than happy usually.

[strad]

Watch the video#2,,simplistic and they aren't scripted so they at times are less than clear,,but if you listen................What got me is Dale Sr. wanted negative caster on the right front.

[machin]

For those who just want to hear the toe-out bit of the video:-

A lot of people say it doesn't matter whether you put toe in or toe out on left front because the driver always drives off the right front because that's the most loaded tyre.

Some people don't see it that way, they say "we want to run toe out on the left front because once the right is more loaded the left is lightly loaded and it gives it more scrub and so it effectively works that tyre harder".

Now, before anyone ( ) comments, I'm not saying I agree or disagree with this... I'm just passing on what the guy on the video said.....

[tomislavp4]

Ok guys since I don´t have the knowledge to write some kind of a sim to test this on, I decided to test it in GTR2.

I changed the toe-out from -0,1 (standard) to 0,4 and than 0,7 degrees and I must say the car feels much more responsive with positive toe out. It is pretty useful on the slow circuits with tight corners but not that much on faster ones. Now I don´t know how accurate these things are simulated in the game but I just wanted to share this

[Jeffsvilleusa]

that´s the point it gives a certain feel to the driver .For lap time it´s not important if your driver does not need that feel for his confidence.When you are able to show him the speed he´s gaining by not dragging the fronts on the straights he´s more than happy usually.

Haven't Red Bull demonstrated you can sacrifice speed on the straights to get it back and then some on the turns?

[Lurk]

@marcush: driver needs to be confident to get the most of the car. He needs to know where the car will go and when he can push or not, he cannot do that without confidence.


Going back to the toe-out at the front, it was explain to me like this - it isn't very scientific so Jersey Tom shouldn't be satisified about my response, but it could at least be a basis for research.

When you turn, the outer wheel is the most loaded and give the direction to follow.
The inner wheel turns more than the outer wheel so "wants" to turn the car even more.
With toe-in, the inner wheel wants to turn the car less and the outer wheel have more work to get the car in position because it is "fighting" the inner wheel.

AFAIK, extreme toe-out is mainly a problem because of tyre wear and drag.
It also affect straight line stability because left wheel wants to go the the left and right wheel to the right - this is why you wants toe-in at the rear: far more easier to control on full throttle.
You can also increase Toe-in (rear) / Toe-out (front) if you struggles to warmup your tyres.

[HampusA]

I´ll give my theory as to why i think Toe out can help the front end initially on turn-in. Probably not a correct theory but here it goes,

Assuming we have a right hand corner, we enter this corner at exactly the same speed with and without Toe out.

If we start with no toe out as a starter, you would turn the wheel let say 90 degrees to make the corner.

With the added Toe out, your left wheel will effectively point out to the left, not much but still.

Wouldn´t this cause you to turn the wheel slightly slightly more to get the left tire in the same angle as the front left without toe as you corner?

If yes, then my theory is that once you gotten the loaded left front tire in the same angle as the non-toe-test you still have a slight advantage due to the right tire pointing slightly more into the turn.

Left side has the most load but the right side tires still have some grip.
So maybe it´s the inside tire that creates this extra feel for turn-in because you have the left side tire in the same angle as the non-toe tire.

Does this make any sense?

[GSpeedR]

There needs to be some consensus regarding the definition of "turn-in". I describe turn-in as the initial onset of steering to negotiate a corner, a change in the vehicle state from straight-line state. This means that slip angles are very small and very close to their straight-line values and wheel vertical load distribution is very close to static (neglecting changes from downforce etc). Lateral load transfer is very small since lateral acceleration lags lateral force, which is also small.

I agree with machin and others who claim that net yaw moments about the CG are responsible for front toe-out to create a faster response. You can visualize this simply by drawing a picture of a chassis in top (plan) view and using vector analysis. SAE convention dictates that lateral tire forces are perpendicular to the corresponding wheel plane, so it is the steering angles that are important. Yaw moments about the CG from lateral force are proportional to the perpendicular distance (moment arm) between the lateral force line-of-action and the CG. With no steering, the yaw moment arm from the front tires will be simply the distance between the front axle and CG. In an extreme case, if a tire's force line-of-action intersected the CG then that particular force produces no yaw moment.

As you add toe-in, the LF tire force-line (vector) begins to rotate towards the CG, as does the RF (direction of this force vector is not important since it will not affect magnitude). This creates less net yaw moment from each front tire's lateral force. The opposite is true when you add toe-out. The force vector rotates away from the CG and the moment arm (and thus the yaw moment into the corner) grows. If you had a symmetric car and your half-tracks equaled your half-wheelbases then the extreme case would occur at a steering setting of 45 degrees. This is a necessity due to the geometrical layout of a 4 wheeled vehicle with a CG inside the 4 wheels.

It is true, that braking forces, including slip angle drag, have an opposite effect. I would argue that a "turn-in" condition indicates the transition coming off the brakes and the building of lateral force. In any case, the above argument indicates a relative change in yaw moment into the corner (SAE convention is negative) regardless of the overall vehicle state. As lateral forces grow and load transfers occur and slip angles change you will need a simulation to observe the overall vehicle balance, but this geometrical effect is still contributing. During the initial stages of steering, I believe it is by far the most significant.