[Subafreak]

Porter is correct. Another example of the fact that a tire with lower air pressure turns faster is this: Ford uses a tire pressure moniter system that uses the ABS sensors to track tire pressure, if one wheel starts turning faster that the others then it's losing pressure and will turn on a warning light on the dash. Personally with an AWD car I think it is a good idea to replace all 4 tires at the same time and rotate them religiously. It may be a bigger hit to the wallet all at once but so is a new tranny.