godlameroso wrote: ↑
Sun Apr 04, 2021 8:01 pm
marcush wrote: ↑
Sun Apr 04, 2021 3:21 am
I fail to see how 1mm more or less toe should affect aero in any meaningfull way , if that was the case the car would simply be impossible to drive in a straight line as any minor correction on the steering wheel would umsettle the car big time.
Big steering input ( also known as induced slip angle) can have aero effects , especially with front suspension and steering geometries aimed at changing rideheights , tyre sidewall deformation under load etc.
static Toe settings add or deduct artificial slip angle to the tyre ,so there is
an influence to be found on how much grip is available as a tyre is slip angle sensitive (there is a optimum slip angle for a given vertical load )
This vertical load -optimum slip angle relation is mirrored in anti ackerman steering geometry : the lesser loaded inner front wheel has more grip with less
slip angle ,thus it makes sense to not steer it “correctly “ but keep it a bit too straight .Thats all depending on specific tyre caracteristics.
When your suspension shows bump steer characteristics , your grip will change through suspension travel as the tyre changes slip angle ...but On an aero car the influence of underfloor ride height change induced vertical load fluctuations is your main enemy .
One quarter of a degree of toe is ~6mm one degree of toe is 4 times that amount, it's not insignificant.
If you run 6mm toe in or toe out this will kill your tyres in no time with a radial tyre toe is not asjusted in degrees , it's
measured as mm or minutes (if you use degrees).
The basic idea is : toe is forced /geometric slip angle ,eg a radial racing tyre is producing maximum grip at say something like 6° slipangle ( depending on vertical force) .
if you preload your tyres with artificial slipangle the result is you produce heat
not grip , as you have to look at all 4 tyres ...the additional angle helps on one side put has also an effect ,most likely an unwanted on the other side of the car.
THIS is the reason for Anti Ackerman steering geometry !
The higher loaded outer tyre wants more
slip angle for max grip the less loaded inner wheel wants less slip angle for max grip .
A tyre at 7° slipangle is at max lateral grip ......so cannot transmit much in terms of longitudinal force ..so toe in and out is also affecting your braking and acceleration.
no wonder Merc had DAS ...there was a lot to be gained...