About BMW Z4 E89 Step 1Toe-In / Out setup

[LazyBug]

I get very confuse when trying to setup the toe-in / out for the car so hope to get some explanation here ... pls have a look the 1st picture below -->

All minimum toe's result: If i " - " both front & rear toe to minimum value then front toe i get 0.5 & rear toe i get -0.23

All maximum toe's result: Now If i " + " both front & rear toe to maximum value then i get front 0.09 (smaller value compare to 1st picture) & rear 0.28 (bigger value compare to 1st picture) ??

So whats the deal here ?? How come one increase another one decrease ?? Also the front tyre dont seen to have negative value so is that mean Toe-Out is not available for front tyre ??

Thanks for the concern.

 

[Pawel Ziolkowski]

Sorry, I just had to make sure we all know what is needed for toe in/out. Taken from http://www.ozebiz.com.au/racetech/theory/align.html

Thank you very much for that link!! I think i get it now.

The thing that confused me was the very definition of turn in. It looks like "turn in" happens before weight transfer, not during it. And the effects of toe on stability are varied by rigidity of suspension and bumpiness of the track.

After trying the lotus49 which has older suspension i see that toe out does defiantly increase turn in. As the books say. But it looks like in more modern cars with rock stiff suspensions this effect is so small that is overshadowed by load transfer effects, which infact create reverse effect.

Just now I tried blind setups with extreme toe (in and out) on Zonda and lotus49 and increased toe gave a feeling of oversteer on zonda while giving understeer in lotus. So i think there is definitely more to toe than it looks on the surface.

I suspect for modern racecars the effect of toe on car handling is quite different than what old books based on older cars tell.

It's quite confusing when it is said that the effect of ie. stiffening roll bars is to increase turn in (quicker load transfer, but less grip later). One then could assume that toe setting increasing "turn in" also refer to faster load transfers, when infact they refer to general stability on straight and over bumps.

In my race sim experience, toe-in at the front will provide better turn in response (i.e.: negative values). I'm not an engineer but as far as I understand it, increasing toe-in (wheels pointing inwards) increases front end grip during lateral forces (cornering) but at the cost of longitudinal grip (i.e.: braking instability). I've never used a car with positive toe (or toe-out) at the front but then again, I hate understeer with a passion so anything that compromises turn-in is bad for me.

On the inverse, as far as I know, increasing toe-out (positive values) on the rear wheels will provide a similar effect of increasing toe-in (negative values) on the front wheels but I would say adjusting toe on rear wheels will probably be more focused on corner exit and not on entry. Though, it's all relative between the front and back of the car so you could have a slight bit of toe-out on the front but a hell of a lot of toe-out on the rear and it could give the same feeling as just increasing front toe-in.

In regards to Assetto Corsa specifically, I just realised that the front values are inverse of the rear :/. So decreasing the values on the rear increases toe-in while increasing the values on the front increases toe-in. I'll mention this in the bugs section of the Assetto Corsa forum since I believe it should be uniform between front and rear.

Yeah and that is (was) my problem, books say toe out = better turn in, sim experiance tells otherwise. Example: http://iracing.wikidot.com/components:toe-in-toe-out, they have a diagram of wheels pointing outwards for better turn in, while as you say "(wheels pointing inwards) increases front end grip during lateral forces (cornering)" and that increased front grip gives a feeling of faster response and oversteer, not stability as the article states.

 

[Celtic Pharaoh]

Yes, "Toe In"=+, "Toe Out"=-.
View attachment 48173

That diagram is wrong. If you even think about it, it's toe-"in" and toe-"out". It's analogically based on feet. You point your feet inwards, thus bringing toes in, is toe-in and vice versa.

 

[Hannes-Joshua Thor Barthel]

wiki says.. toe out are negative values and toe in are positive values... and in all sims I drove a negative toe in ..so toe out... value gives better turning....

 

[LazyBug]

Very very confuse ... some say this some say that ... but from all those guides & articles that i've read:

1. Negative value = Negative toe-in = More toe-out (the front part of the tire is pointing towards the outside of the car)
2. Positive value = Positive Toe-in = More Toe-in (the front part of the tire is pointing towards the inside of the car)

Or wrong again ??

 

[Andrey Varlamov]

That diagram is wrong. If you even think about it, it's toe-"in" and toe-"out". It's analogically based on feet. You point your feet inwards, thus bringing toes in, is toe-in and vice versa.

The diagram is correct, look at the steering wheel - it's just a front view of the car.

Very very confuse ... some say this some say that ... but from all those guides & articles that i've read:

1. Negative value = Negative toe-in = More toe-out (the front part of the tire is pointing towards the outside of the car)
2. Positive value = Positive Toe-in = More Toe-in (the front part of the tire is pointing towards the inside of the car)

Or wrong again ??

You're right.

 

[LazyBug]

Another one --

Since the technical name for this setup is call "Toe In" so i guess it make more sense Toe-out = negative value & Toe-In itself is positive value.

 

[Oemie]

wow, this is hella confusing. I always thought negative numbers was toe-in, as I can understand why that would aid cornering (as with the weight on the outside, those tires would form something of an arch). Turns out, what I thought was toe-in, is actually toe-out.... and I still don't understand how/why pointing the wheels outwards would help with turn in... Then the inside front wheel would turn more (which I do sort of see would be helpful), but that's not the one that holds the weight. Is it to get some sort of wishbone suspension effect, where the inside wheel is turned more than the outside?

What madness did you start, LazyBug!!?

 

[Maciej Dolinski]

From what i understood:
Game tooltip

Negative value - TOE-OUT
Positive value - TOE-IN

TOE-IN front - wheels point towards each other creating stabilizing force on straight. When turning inside wheel looks "away" from corner so it works against force generated by outside wheel decreasing car turn-in response.
TOE-OUT front - any steering change will cause one of the wheels to point more toward outside of a car increasing turn-in response.

I assume turn-in is a moment when car start to respond to driver input, and not steady state when all weight moved to one side. But even then TOE should still have some effect. TOE-OUT will make inside wheel look more towards corner (affecting ackermann). So it will try to steer in tighter radius than outer wheel creating additional slip and more cornering force (inner wheel travels along shorter turn radius than outside wheel so it need to be turned more).

 

[Pawel Ziolkowski]

While I'm still researching the relation of toe and turn in/stability, I think got to the point i could explain it a little. (still not 100% sure if correct)

Before load transfer (due to acceleration of whole car), toe-out gives better turn-in.
This is most apparent on bumpy tracks, with simple, soft suspension (not limited to springs, but general geometry stiffnes - rubber joints etc.). That's because when the wheel go over bump it will bend the suspension and the steering in that wheels direction. When car has toe out it increases the bump loaded wheel slip angle generating a turning (destabilizing) force for the car.

After the car starts to rotate, the horizontal acceleration will shift the load from inside to outside, and as in the picture i posted here earlier (http://www.racedepartment.com/forum...89-step-1toe-in-out-setup.80590/#post-1615751) toe-out will stabilize the car.
Because soft suspension move slower than steering input, this latter effect will be harder to notice when turning in. (It will be noticeable when operating throttle/brake and driving over big bumps/kerbs with constant steering input).

Now the problem with modern racecars/supercars is that they have 1) advanced suspensions that doesn't bend much over bumps 2) steering that is quite resistant to bumps and(*) 3) lightning fast weight transfer.
This three effects lower the turn-in effect of negative toe, while the really fast weight transfer increases stabilizing effect of negative toe.

This is why i believe on modern cars, and especially on flat tracks it's better to control turn-in with other setup features, and if anything add positive toe on fronts for increased dynamic front end "bite".

(*) I've read about differences in sims vs RL, that for GT racecars you get less feedback from the wheel than in sim actually, and the steering is just rock solid, even over bumps.

I assume turn-in is a moment when car start to respond to driver input, and not steady state when all weight moved to one side. But even then TOE should still have some effect. TOE-OUT will make inside wheel look more towards corner (affecting ackermann). So it will try to steer in tighter radius than outer wheel creating additional slip and more cornering force (inner wheel travels along shorter turn radius than outside wheel so it need to be turned more).

The problem with ackermann is speed, most racecars run almost no ackermann angle at all. Because of 1) large turn radiuses 2) minimal steering even on slow corners (thus minimal ackermann angles) and 3) almost no load on inside wheels meaning that during turn it doesn't really matter in what direction the wheel is pointing. (For example, search for F1 videos with Hamilton when he was racing for McLaren, his inside front was sometimes flying over the track right before apex.)

Also when comparing wheel slip angles of toe-in and toe-out, we cant just look at one tire. Yes the inside wheel will have more slip with toe-out. But the same will be true for outside wheel with toe-in, and it's the outside wheel that has more load, thus the same slip angle will generate more lateral force.

 

[LazyBug]

What madness did you start, LazyBug!!?

From all online articles that i read Toe-Out = Negative value example like "-0.5" & Toe-In = Positive value example like "0.5" & how they affect cornering ??
Check this out: http://www.ozebiz.com.au/racetech/theory/align.html or http://www.wheels-inmotion.co.uk/tech-wheeltoeintoeout.php
I manage to lap 0.6s faster driving Z4 E89 Step 1 in Magione modified the setup according to what i had understand about toe so far

 

[Oemie]

Thanks, now I get it:

If the car is set up with toe-out, however, the front wheels are aligned so that slight disturbances cause the wheel pair to assume rolling directions that do describe a turn. Any minute steering angle beyond the perfectly centered position will cause the inner wheel to steer in a tighter turn radius than the outer wheel. Thus, the car will always be trying to enter a turn, rather than maintaining a straight line of travel.
​

So, as Stary_Precel said, it's not when under load, but prior to it. The inner wheel wants to turn really before the real load transfer happens, so indeed, it is really on turn in only, but not while the weight is on the outer tires through the turn.

I guess for increased track contact through the corner, you'd use camber, then.

 

[Maciej Dolinski]

...
Also when comparing wheel slip angles of toe-in and toe-out, we cant just look at one tire. Yes the inside wheel will have more slip with toe-out. But the same will be true for outside wheel with toe-in, and it's the outside wheel that has more load, thus the same slip angle will generate more lateral force.

Now I feel lost.

If outside wheel reaches perfect slip angle then:

- with TOE OUT inner wheel will point more towards corner providing additional cornering force.

- with TOE IN inner wheel will face away from corner working against turn.

I assume outer tire have ideal slip angle because this is driver job to find it’s maximum grip level. I don’t know how it matters that with particular steering angle with TOE OUT wheel will be turned a degree less than with TOE IN. Driver can just turn wheel to get this one degree and find optimum grip.

 

[Risto Kappet]

I see walls of text which none respond to OPs problem.

If the toe adjustor itself does not do it, then also change rideheight and every other suspension setting that changes it. They sometimes have even bigger effect to toe (and camber)
Then you can get both ends to get toe in or out as much as you want.

 

[LazyBug]

From what i had read in this 2 weeks FWD should has Toe-Out (Front) / Toe-In (Rear) while RWD should has Toe-in (Front) / Toe-Out (Rear).
Dont ask me why, i dont know how to explain but all i know is that i really lap faster by setup the car according to this rule in AC.
And then Toe-Out assist turn-in but less stable in braking and more tyre wear while Toe-in more stable in braking / less tyre wear but less responsive turn-in.
Thats all i know & thats more than enough for me to know

 

[Andrey Varlamov]

FWD should has Toe-Out (Front) / Toe-In (Rear) while RWD should has Toe-in (Front) / Toe-Out (Rear).

Maybe vice versa?

 

[Pawel Ziolkowski]

Maybe vice versa?

Agreed. While toe on the front is more of a preference the general values of toe for the rear definitely should be "out" for FWD and "in" for RWD (to fight the throttle-on tendencies on corner exit - understeer for FWD and oversteer for RWD)

 

[LazyBug]

Maybe vice versa?

Honestly i dont know but here is the explanation:

As a front-wheel-drive car pulls itself forwards, the wheels will tend to pivot arount the king-pins, and thus towards the center of the car. To ensure they end up straight ahead, they should sit with a slight toe-out when at rest.

A rear-wheel-drive car pushes itself forward, and the front wheels are rotated by friction... thus they will tend to want to trail the king-pins, and therefore will want to splay apart. To ensure that they run parallel when rolling, they should be given some toe-in when at rest.

 

[Andrey Varlamov]

Honestly i dont know but here is the explanation:

Hmmm , but from Pointed the Right Way:

it is rare to set up a rear-drive race car toed out in the rear, since doing so causes excessive oversteer, particularly when power is applied. Front-wheel-drive race cars, on the other hand, are often set up with a bit of toe-out, as this induces a bit of oversteer to counteract the greater tendency of front-wheel-drive cars to understeer.

It's all so confusing .

 

[LazyBug]

Another one to keep people confusing

A Focus and almost all front wheel drive cars have TOE-OUT in the front. This is reflected by "negative" numbers on the alignment specs (TOE-IN are the "positive" numerals). Why toe out on the front? Its simple physics. As the tires pull themselves forward (aka torque) they pull themselves into the desired toe-in position. In essence it's a self compensating. Once at a consistent speed the resulting front toe ends up being a tiny bit inward. Just enough to allow that directional stability that is needed. If the toe is set to far out it never gets to the proper amount of toe-in when the car is moving. What are the downsides besides bad handling....tire wear. Too much "toe-out" causes inside edge tire wear (toe-in causes the outside edges of the tire to wear). Combine it with camber and it only amplifies the problem. Another thing to consider, the alignment specs were determined using factory bushings. When you install harder bushings, the wheels may not be able to pull themselves fully back into the desired toe-in position. Watch yours tires carefully for wear after installing bushings and be prepared to reduce the amount of initial toe-out if wear is occurring.

Source: http://www.focusfanatics.com/forum/showthread.php?t=143550

By the way may be its cause by the purpose of the car ?? I mean we dont set our daily use car as the same compare to racing car. One aim for safety purpose one aim for racing ??

 

[Pawel Ziolkowski]

By the way may be its cause by the purpose of the car ?? I mean we dont set our daily use car as the same compare to racing car. One aim for safety purpose one aim for racing ??

Road cars and racecars are definitely set up differently. With road cars the biggest concern is minimum rolling resistance / tire wear, so you want to have 0 toe angles when driving. But because of forces acting on suspension bending the wheels when driving, you need to compensate that with non-0 static values.

For racing its most important how the car behaves in transitional periods, like over bumps, and when applying inputs (steering, throttle, brake) so the static toe values are set in a way that gives wanted values during these short transitions (and depend heavily on car/track combo). So they will vary widely from road car values.

As Andrey Varlamov pointed out, your values of rear toe are backwards to what is standard (not saying they are bad, as it all comes down to driving style and car specifics, but just "standard").

And for front toe, there is so many factors influencing it that there is no standard. Racing books, articles, etc usually deal with concrete car/track combination (which is usually not a racecar used in professional racing as you are trying to set up). Thats why they can state "standard" toe values. But from what i understand, there is no magic standard for all cars.