Scotty,
How much difference is really allowable in tire tread depth on these vehicles? Does the computer have a way to read the normal variation in wheel rotation and compensate the threshold to trigger traction control, or are these systems strictly coded to look for zero difference. The dealer tells us we can't have more than 2/32" (1/16") in tire radius. Is this just bull scat or is there a real problem? If it's as bad as they say, how could these cars turn tight corners???? It would be great to see a video on this that covers makes, years, and models on how well or poorly manufacturers have dealt with this. As a retired engineer, I know how easy it is to program a computer to learn and fudge expected ideal conditions. I'm really TIRED of buying 4 tires when one goes bad! Once is enough! {black}:idontknow: {black}:displeased: {black}:gape: {black}:shocked:
It's not the computer or the traction control, it's Subaru's complex AWD system, which has front, rear and mid-car differentials. If the tires are different sizes, it makes the differential gears and clutches in the AWD system overheat and/or wear out faster.
Having to replace all four tires at the same time is one of the drawbacks of full-time all-wheel-drive systems. If the difference in diameter is too great you have constant slipping in the differentials and limited-slip clutches instead of just when turning corners, and those parts will wear more quickly.
There are some tire shops equipped to shave a new tire down to match the others.
