928s2 left wheel spinning
07-27-2015, 07:04 AM
#1
Track Day
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928s2 left wheel spinning
if its wet or loose surface the left rear wheel spins up really easy
this tyre seems to have a lot more wear than the right one but it also lurches the car sideways from time to time in the wet
wondering if this is normal
this tyre seems to have a lot more wear than the right one but it also lurches the car sideways from time to time in the wet
wondering if this is normal
07-27-2015, 07:32 AM
#4
Rennlist Member
Obviously you have no limited slip diff and if that wheel is the one that keeps spinning then obviously it will wear faster.
The reason for slipping predominantly on that wheel is probably to do with corner balance being out of whack. The 928 is designed to distribute weight evenly on all 4 wheels with something in the region of 400kg on each wheel. When the corner balance is out too much weight hangs on one of the diagonal axes- think of it like a chair with one leg shorter than the others- the chair floats on the diagonal with two equal length legs flopping back and forth on the short leg axis. This happens with weight load.
Thus the axis that is "lightly loaded" will break traction first given it is trying to apply the same torque to both and when it breaks loose all the power goes to the spinning wheel.
If you can measure the corner loadings you should see the rear left wheel has a lighter loading as will [likely] be the case with the front right wheel. To solve this you need to either lower the left rear ride height or increase the right rear ride height [or a combination of both]. For purposes of experimentation you can try this in increments of say three turns of the adjuster nut [assuming it is not seized solid] but remember that as you change ride height you will also change the toe and camber. If you find improvement that you like you then need to check the alignment.
Trust I have got that lot the "right way round" - others can correct if I got it wrong.
There could also be other reasons for a tire not gripping such as too much camber on one wheel, too little toe-in on one side or rubber that has simply gone off due to age hardening [was one tire replaced before the other?] - you should also eliminate these possibilities.
Rgds
Fred
The reason for slipping predominantly on that wheel is probably to do with corner balance being out of whack. The 928 is designed to distribute weight evenly on all 4 wheels with something in the region of 400kg on each wheel. When the corner balance is out too much weight hangs on one of the diagonal axes- think of it like a chair with one leg shorter than the others- the chair floats on the diagonal with two equal length legs flopping back and forth on the short leg axis. This happens with weight load.
Thus the axis that is "lightly loaded" will break traction first given it is trying to apply the same torque to both and when it breaks loose all the power goes to the spinning wheel.
If you can measure the corner loadings you should see the rear left wheel has a lighter loading as will [likely] be the case with the front right wheel. To solve this you need to either lower the left rear ride height or increase the right rear ride height [or a combination of both]. For purposes of experimentation you can try this in increments of say three turns of the adjuster nut [assuming it is not seized solid] but remember that as you change ride height you will also change the toe and camber. If you find improvement that you like you then need to check the alignment.
Trust I have got that lot the "right way round" - others can correct if I got it wrong.
There could also be other reasons for a tire not gripping such as too much camber on one wheel, too little toe-in on one side or rubber that has simply gone off due to age hardening [was one tire replaced before the other?] - you should also eliminate these possibilities.
Rgds
Fred
