different tire diameter front to rear

[Rich8]

I have an 1991 850i and a 1997 840Ci (one with OBD I and one with OBD II), and want to change the tires, but what I want would have a bigger diameter on the rear than the front. I am thinking this will mess with the Traction Control.
I know it is possible for someone with the right scanner, to get into the on-board computer and adjust some of the settings. Is it possible to reset the front and rear diameter so the car will compensate for the 0.7" diameter differance?

[JustinE36M3]

unless its awd, even then, i dont think it should be a problem. <-- dont take that for a correct valid answer

[pbonsalb]

ABS and TC sense a speed differential between the wheels, so if the circumferences no longer match as closely as the factory, those functions may not perform as well. I do not know how far you can stretch things, but I would not worry if you are within a few percent.

If you are simply running larger or smaller circumference tires, but the difference front to rear is about the same as factory, I think that all you might screw up is your speedometer and odometer accuracy. This may depend on where the speed is measured. Could be the differential or could be at the wheel.

[Jim@tirerack]

If the diameter front to rear is off it will also throw off anti lock brakes. I would not recommend it on either car. You can go with a wider wheel and tire but not taller.
If I can help let me know.