Anyone know what the tolerance is in the ABS program for staggered tires sizes front to rear? I am running a 40 series in the front and a 50 series tire in the rear. I realize this is not the ideal setup and I have another set of 50 series tires in the garage to replace the fronts, but have not had the time to change them. My ABS light comes on after 2 minutes of driving, but it is due to a bad ABS sensor as even with the same series tires front to rear the light comes on. Curious. Mr. T.

I don't think absolute wheel speed is the critical factor in ABS operation when braking force is not being applied. Anytime you are turning, the outside wheels are rotating faster than the inside wheels. ABS senses loss of rotation of any wheel or wheels when brakes are applied and will modulate braking pressure to that wheel or wheels. Even if the tires are not the same size, the system develops a profile of what all the wheels are doing based on the inputs from the speed sensors. If one shows a sudden loss of velocity, that's the one that get the attention and adjustment from the ABS. If the front tires are smaller and turning faster, then a sudden loss of rotation will be managed by the ABS no matter what the tire size is. The diametric difference of a 40 aspect ratio versus a 50 aspect ratio tire is probably not enough to cause problems.

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Jeff Lawrence
1987 300e
1989 300e
2000 Dodge Grand Caravan SE