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.

 

[Ales Nocar]

EDIT: delete

 

[Maciej Dolinski]

TOE OUT (wheels poining outwards) is usually used in front to increase car turn-in response. If setup allows front TOE to have only positive values I would assume it indicates TOE OUT. So probably TOE in "car status" indicates TOE OUT when positive and TOE IN when negative.

 

[LazyBug]

So probably TOE in "car status" indicates TOE OUT when positive and TOE IN when negative.

I dont understand this since there are no negative value even i use the minimum value ... its very confusing to me.

 

[Pawel Ziolkowski]

TOE OUT (wheels poining outwards) is usually used in front to increase car turn-in response. If setup allows front TOE to have only positive values I would assume it indicates TOE OUT. So probably TOE in "car status" indicates TOE OUT when positive and TOE IN when negative.

Woha woha, I don't know what clever books about racing setups on superfast road cars say, but from engineering standpoint this have no sense.

Wheels pointing inwards (toe in) should help the car turn in. Since when we start steering, the load will start to shift from inside to outside wheel. For positive toe-in the outward wheel (more loaded) will then have more slip angle than the inside one, thus we'll get more load on higher slip angle faster, generating cornering force faster and helping the initial turn in.

As for setups, from what i know, the AC cars are modeled as close to the real ones as possible, so i wouldn't be surprised if real car had only +0,09 to +0,5 front toe-in.
And for setup number, i believe they based the numbers on real life as well, and these settings often don't have constant correlation with actual angle on the suspension.
This might be confusing and maybe they will clear things out but from what i've read on AC forums they are using numbers used on real vehicles as provided by manufacturer, and racing teams input. And I wouldn't be surprised if there were inconsistencies in designations IRL too.

 

[LazyBug]

Wheels pointing inwards (toe in) should help the car turn in. Since when we start steering, the load will start to shift from inside to outside wheel. For positive toe-in the outward wheel (more loaded) will then have more slip angle than the inside one, thus we'll get more load on higher slip angle faster, generating cornering force faster and helping the initial turn in

I dont know but from all the setup guide it say toe-out help turn in, not toe-in .. example this from nK-pro setup guide -->

Edit/Effect:
– Open toe (Toe Out) = quicker steering response, make the car turning into a
corner quicker, less stability
– Close toe (Toe In) = slower steering response, make the car turn slower into a
corner, car more stable"

And this is from Race 07 setup guide --
Toe In With Toe-in at the front or rear you can adjust the degree the front of the wheels angle towards or away from each other. Toe-in is used for directional stability and initial corner turn-in.
For the front wheels, the preferred setting is a slight amount of toe-out (negative setting), which helps turning in.
For the rear wheels, the preferred setting is toe-in (positive setting) because toe-out creates instability.

So toe-out for front wheel & toe-in for rear wheel looks ideal .. right ??

 

[Pawel Ziolkowski]

I dont know but from all the setup guide it say toe-out help turn in, not toe-in .. example this from nK-pro setup guide -->

Yeah you are right, many resources point that front toe-out gives better turn in. But they never explain why exactly.
In LFS i added toe-in for better turn in and it worked quite nice.
Also just now i tested Fabarth @ drift, full throttle until the first turn out of the pits, then turn and liftoff at a fixed point. With positive toe in i was almost hitting wall at the right, with negative toe-in (toe out) i was almost on the grass. There were more instances in AC and other sims where adding toe in helped with turn in, or adding toe out helped with braking stability (front wheels)

This of course isn't in any way conclusive, but as an engineer IRL this is the only way i see toe could work.This forums have a lot of experienced people, so i'm hopeful somebody comes here and prove me wrong if that's the case.

edit: anyways its probably more to do with naming conventions than bad physics.

 

[LazyBug]

Here is what i learn given by a member from AC official forum ..

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.

So looks like thats depend to if the car is FWD or RWD

 

[Pawel Ziolkowski]

Here is what i learn given by a member from AC official forum ..
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.

So looks like thats depend to if the car is FWD or RWD

Yeah but unfortunately that only describes what happens during acceleration (and braking).
The concern here is (for sim or RL) that the toe measured while stationary will shift a little while driving because the suspension isn't perfectly rigid. (I've actually remember having this on classes in basic vehicle design hehe , it's nice that modern sims can simulate this)

From what i've read on the matter, one thing worth noting were the differences on the actual definitions on directions. Some articles talked about toe in some about toe out some about negative toe in/out and some even had pictures showing opposite of what was written.

I'm pretty confident in my theory but it does contradict most sources so until we get some definite answer from somebody who actually works on the racing cars. I would just go by the feeling. Try both heavy toe-in and toe out and pick the one with more turn in, or if you see no difference leave at default value.

edit: Heey a badly drawn picture!! This is how i see effect of toe on front wheels in regards to the initial turn in. (Of course everything is overblown and, and happens right at the begining, before the car even settles itself in the turn.)

(bloody paint in win7 is useless, damn i want my XP paint back! If win8 followed the "improvements" it must have like two colors and one brush at most )

 

[Maciej Dolinski]

Well in your picture TOE IN creates forces pointing towards car center. So on turn-in force generated by right tyre should still exist working against forces generated by left tyre. I would guess this is why it would decrease car response. Also when cornering right tyres are closer to apex so turn radius for them is slightly smaller than for left tyres. For right tyre to have same slip angle as left tyre it need to point a bit more towards the turn.
Also I reserve my right to be completely wrong.

 

[Arkadiusz Wawrzyniak]

So... In AC we have toe in setting and most of the cars can't get negative values. Does that mean that positive toe in is making toe in stronger ?
And also what are desired values?

 

[Pawel Ziolkowski]

Well in your picture TOE IN creates forces pointing towards car center. So on turn-in force generated by right tyre should still exist working against forces generated by left tyre. I would guess this is why it would decrease car response. Also when cornering right tyres are closer to apex so turn radius for them is slightly smaller than for left tyres. For right tyre to have same slip angle as left tyre it need to point a bit more towards the turn.
Also I reserve my right to be completely wrong.

In the picture above i assumed the same magnitude of toe for both "in" and "out". In Toe-out left tire is working against turn direction, and since it will be the more loaded tire several miliseconds later, it will mean that steering response will be slower.

As for the second part about corner radius, that's why in normal cars we have something called Ackermann steering. Wiki has quite nice take on this, with pictures.
http://en.wikipedia.org/wiki/Ackermann_steering_geometry
Although this is used for road cars mostly, since in racing we rarely ever make very sharp turns (hello Monaco ) and the load on the inside tire is so low that it this effect does not change much. I'm not sure to what extent and on what race cars it the ackermann used but i heard not many. (this and LSD is why you hear tire screeching on some cars when moving around in pits.)

So... In AC we have toe in setting and most of the cars can't get negative values. Does that mean that positive toe in is making toe in stronger ?
And also what are desired values?

That's what i think, more toe in = more turn in, although even the damn books like renown "speed secrets" by Ross Bentley tells that it's toe out that gives better turn in (is the physics in america backwards? )

As for desired values i would use what is needed the most on given setup/car/track combination.
ex: Zonda @ Mugello i run negative toe in to help with balance under heavy braking in T1 as the car turn's in quite nicely already. (Im two places down on you @ RSR at that combo )

 

[Hannes-Joshua Thor Barthel]

I am not an engineer or mechanic.. and some car setup things still give me headaches .. but across all sims I've driven yet.. toe out (more negative toe in) gives a "pointier/faster" initial turn in

also in AC... the only thing which is a bit strange..and where I think the setup screen should become more streamlined across all cars.. for the final version... is that at some cars the value slider is set to the toe out (negative toe in) on the front.. and to toe in on the rear.. at other cars it is both at toe out.. and so on..

I was quite confused with the setup screen in AC too at the beginning.. coming from other sims.. but after just reading the "diagnostic screen" next to it.. it got better... however if in somecars still only the word TOE without in or out is shown... that is indeed still very confusing then.. because you don't know if it is negative or positive toe in or toe out...

I gladly know from other sims (and this toe thing gladly behaves everywhere more or less similar) to know after a test drive in which direction it goes..
however for people getting new into this with AC... it could be very confusing... (beside they already don't have a clue what all that things are if they are realy new... and then add to that these vague parameters of AC it could be realy hard for them.. if they for example try to learn it with theoretical books and such stuff... because it's often reffered as toe in... and toe out is often just displayed as negative toe in... however if AC now displays at some points toe in and at other points toe out...it can get very hard and strange then.. and even more if it just says toe without in or out... so I think streamlining the values / parameters in the setup across the cars is quite importend)

 

[Hannes-Joshua Thor Barthel]

I just wikipediad around... seems.. that negative toe is alsways toe out and positive toe always toe in ... so it's correct to just call it TOE without in or out.. so if the number is positive it's always toe in.. and if the number is negative it's always toe out..

but they still need to streamline the setup... because it's confusing that you have to decrease the value slider at some cars and to increase it in others to get the same direction


after reading more about it... maybe they did it this way.. because they are not referring to the actual. toe with that value but to the.. don't know the english word for it... I just call it "steering bar" for now... or better to the single points of each wheel connected to it..
so it depends wether that thing is in front or behind that "geometrical axis/axle"

that would make sense then... but then the word Toe for that option is a bit strange I think... or are these points actually called "toes" ? I don't know but I don't think so

However I am not a mechanic or so... but after reading more how steering works in wiki... the setup of the toe and that stuff in AC suddenly makes more sense and it explains why you have to increase that value at some cars and to decrease it at others...
so you are not setting up the value for the toe in or toe out itself.. but the point from where it is "toed" which depends on the steering geometry then if you have to increase or decrease it...

and because we often.. or at least I don't know how the specific car is built it was confusing... that's why I wouldn't had any clue if I toe it in or out.. without the "diagnostic screen" (and without driving)



so maybe no need for "streamlining" the setup... but maybe instead a little lesson about car geometry.. for people like me who don't have a clue about such things

interesting on what ideas people came .. what they engineered and developed.. etc

 

[LazyBug]

I actually wondering how come no racing game provide something like a "Tuning Tutorial" where the game give player a bad tune car and guide step by step like this --

1st step: Player have to drive this bad tune car for at least 10 laps & achieve a target lap time for at least 4 laps to unlock 2nd step.
2nd step: Player can now adjust tyre pressure ONLY and a new target lap time is given for player to beat before go to next step.
3rd step: Player can now adjust brake bias & disc size & again another new target lap time has to beat to unlock the next step & next step again until player finally fine tune the car & beat the final target lap time & win the "Bronze / Silver / Gold" achievement depend on the choosing difficulty... good idea ??

 

[Celtic Pharaoh]

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.

 

[LazyBug]

I thought toe-out = negative but toe-in = positive value ??

 

[Kristóf Kerekes]

I actually wondering how come no racing game provide something like a "Tuning Tutorial" where the game give player a bad tune car and guide step by step like this --

1st step: Player have to drive this bad tune car for at least 10 laps & achieve a target lap time for at least 4 laps to unlock 2nd step.
2nd step: Player can now adjust tyre pressure ONLY and a new target lap time is given for player to beat before go to next step.
3rd step: Player can now adjust brake bias & disc size & again another new target lap time has to beat to unlock the next step & next step again until player finally fine tune the car & beat the final target lap time & win the "Bronze / Silver / Gold" achievement depend on the choosing difficulty... good idea ??

The problem with that is someone that is experienced with sims can adjust to bad setups to get those "target times", which are usually not difficult. If they would be actual challenges, then people would start whining about the difficulty level being impossible. But at least, I can imagine myself going for the gold time with the base setups.


On topic: Negative toe -> toe in, vice-versa

The setups are car dependant, it doesn't matter if you can't achieve toe in, it's probably that way in real life then on that specific car.

 

[Tim Ling]

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

When the wheel on one side of the car encounters a disturbance, that wheel is pulled rearward about its steering axis. This action also pulls the other wheel in the same steering direction. If it's a minor disturbance, the disturbed wheel will steer only a small amount, perhaps so that it's rolling straight ahead instead of toed-in slightly. But note that with this slight steering input, the rolling paths of the wheels still don't describe a turn. The wheels have absorbed the irregularity without significantly changing the direction of the vehicle. In this way, toe-in enhances straight-line stability.

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 it's clear that toe-out encourages the initiation of a turn, while toe-in discourages it.




With toe-in (left) a deflection of the suspension does not cause the wheels to initiate a turn as with toe-out (right).


The toe setting on a particular car becomes a tradeoff between the straight-line stability afforded by toe-in and the quick steering response promoted by toe-out. Nobody wants their street car to constantly wander over tar strips-the never-ending steering corrections required would drive anyone batty. But racers are willing to sacrifice a bit of stability on the straightaway for a sharper turn-in to the corners. So street cars are generally set up with toe-in, while race cars are often set up with toe-out.

 

[Andrey Varlamov]

I thought toe-out = negative but toe-in = positive value ??

Yes, "Toe In"=+, "Toe Out"=-.