Quote:
Originally Posted by cwebster
I haven't seen any evidence that engineers built-in a non-documented booby-trap for tire sizes like they did for the torque management. I know other SS drivers have reported problems with different size tires but I haven't been able to pin anyone down to the actual cause. If there is some formula for tire size matching I haven't figured out what it is yet. Maybe someone else will try a shorter tire on their SS and let us know. Maybe you could borrow a shorter pair for 1 pass at the track just to see if they work.
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I've posted already in a 26" tire thread but I'll repeat it. Tried 26" rear tires on an SS (275/40-17 Mickey Thompson) with stock SS-size front tires, namely 245/40-20 Michelin PS4S. Before I even drove the car I changed the tires revs/mile in the tune to what MT said for this tire. Did not even get 1/2 mile in first drive with these tires and the car felt like it would not go, the computer was obviously mad about the difference. By disabling the nannies (the long hold on the TC button until the lights come on in the dash indicating stabilitrack is off) was able to drive the car. However on the dragstrip, I saw the 'Service Stabilitrack' message flash on the dashboard and my log showed a timing retard event that coincided with seeing the error. So turning the nannies off wasn't enough.
Had also run the car with MT 305/45-17 rear tires (28.1" per MT) and stock-size fronts without having these issues. It seems the computer doesn't much care about the rear wheels spinning slower than the front wheels, but objects to them going faster.
Because of this experience, my suggestion to someone with an SS who runs tires on the rear that are shorter than the front tires to this extent, is to remove the 2 ABS fuses when they race the car. Power steering is lost and there are lights nagging on the dashboard, but that's not really such a big deal. The reason for this suggestion, of course, is that the computer won't have data on front wheel speed vs rear wheel speed when the ABS sensors are powered off.