Toe-in/out sensitivity on different lateral levels

[sierra4000]

Hello,
How racing tire is sensitive on any toe changes over full lateral load range?
for example:
Is toe-out (always) more significant change when tire approach his lateral limit ?
Is same effect for both axles?
Is just reason why want minimum compliance steer,roll steer on rear axle?

Thank you for comments

 

[GregLocock]

Static toe setting is an important part of the linear range understeer for some vehicles. On the model I'm working on I have to check that the static toe is within 0.1 degrees of nominal after each change (I don't like the automatic aligner). On live rear axles a touch of toe-in is often a good idea.

I didn't really understand the rest of your question. I think you are asking if compliance steer is significant. Yes it is.



Cheers

Greg Locock


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[sierra4000]

Thanks Greg,
again excuse my english,

I try better understand tire behavior
so
1) if zero toe we can use like a basic value and car go up to max lateral level..............that tire slip angle development is reference
2) when static toe-in is increased +0,1 Degree, is same effect up to limit?
3) then gradually again and again +0,1 Degree............same effect?
4) vice versa toe-out effect?
5) same effect for compliance or roll steer, because only resultant toe value is important on specific lateral level?

I hope you understand better

 

[cibachrome]

For the couple dozen of racing (slick) tires I have test data on, they all show that a pair of them on 1 axle at any amount of load transferred prefer a ZERO toe setting (as in parallel steer) at maximum axle capability. Not at all the same for the many more passenger car and truck tires in my hive. Toe-out seems the be the winning majority alignment setting for them. These results are not from a vehicle simulation running a Max Lat test procedure, but from an organized process (in Matlab) that sweeps thru toe-in to toe-out as fixed load transfers are applied during slip angle sweeps. Mz and Mx and camber contributions are not considered. There are a few verbose self nominated 'author-ities' who state that lateral force characteristics are all that matter, anyway. Do the math or the testing yourself and avoid the hassle of non-ending speculation.

This should give you some relief because if it were any other result, the non-steered axle's force output would not be as good as the front's unless some absurd compliance or kinematic toe change effect could be configured (NOT just "4 wheel steering", that doesn't improve max grip at all.) That generally means a low understeering rice cah becomes a loose cannon when the going gets rough.

 

[sierra4000]

We can generally simplify that toe setting and his changes during lateral load or roll is most important in low g range and is use for straightline stability and transitional maneuvers but when car closer to limit then will require get close zero for maximize cornering capability?

 

[GregLocock]

That depends. If your ackerman curve is perfect then yes. But more than one famous racer has said that ackerman is rather a long way down their tuning list. One approach is to decide on your slowest corner and then tune the toe on that corner.

Cheers

Greg Locock


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[sierra4000]

I like parallel steering idea. And how the camber must be considered in this toe question?

 

[GregLocock]

I don't know how you tune camber settings on a race car. On a road car there is a weird (in my opinion) graph of desired camber vs static toe for optimum tire wear. So that defines the limits we use, then one of the golden bums goes out and tries a few settings.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?