I just bought new wheels, and i have 2 used tires and was planning on buying 2 brand new ones. I recently heard from 'someone' that i have to put 4 new tires on. Is this true? because, it seems to me that if u got a flat it would be absurd to have to buy 4 brand new tires. please let me know guys. thanks! - chop

IIRC, the difference in overall circumference between the new and old tire can be no more than .25" ... hopefully, someone can clarify, but I believe this is measured with tires mounted on the rims, not just the tires by themselves

Originally posted by Rojorex
IIRC, the difference in overall circumference between the new and old tire can be no more than .25" ... hopefully, someone can clarify, but I believe this is measured with tires mounted on the rims, not just the tires by themselves
Yep. From my.subaru.com:

On All-Wheel Drive (AWD) vehicles, it is extremely important that the rolling or outer circumferences of the tires be within 1/4 inch of each other. This means that you must physically measure the size of the tire. This is best done with the weight of the vehicle off the tire and at the tread centerline. Also be certain that the tires are properly inflated since this can affect your readings.

If you need to replace just one tire, the same holds true. The measured difference in circumference between the replacement tire and the other tires on the vehicle cannot exceed 1/4 inch.

Depending on the vehicle mileage, it might be better to replace all four tires.

If the vehicle mileage is low and the tires have been rotated and driven at the proper inflation pressures, then you may be within the allowable 1/4-inch difference in circumference.

If the difference between the new/replacement tire and the current tires is within this 1/4-inch maximum, then the tire should be compatible. If it is not, then other tires will need to be replaced to conform to the 1/4-inch rule.

Exceeding this 1/4-inch difference in tire circumference can place unnecessary wear on drivetrain components, possibly causing them to wear out prematurely.


-Dennis