Replacing Tires

I assume you have an automatic transmission. Any difference in size (due to wear or different manuf./model) could be detected as poor traction and cause the clutch pack to engage. If that happens on dry pavement, 'torque bind' could lead to drivetrain damage.

You 'should' have tires of the same size (Subaru was recommending circumferences within 1/4" - maybe that has changed)

You 'might' get by using the FWD only fuse under the hood. I guess they still have that option. Check your manual on spare tire usage/ emergency flat etc.

You 'might' investigate having a tire shaved to match the other 3. I doubt shaving 2 tires is worthwhile. 1 might be if it isn't $$$.

Just buy one new tire and have it shaved. Tire shop here in town does it for $20/tire.

You could also have an issue with the stability control. My father had his tires rotated on his Lincoln Towncar and had all kinds of issues with the engine power being cut. Turns out one pair or tires was slightly smaller (diameter) than the others, and when the smaller ones were on the back, the computer kept cutting power because they rotated slightly faster than the fronts, and the computer thought they were slipping!

Dan D '99 Impreza 2.5 RS (son's) Central NJ USA

afaik, you risk stripping the differentials if all the tires aren't the same size (within 1/4" circumference!). remember, with awd there's also a differential front to rear, so it's not good enough to just match pairs on each axle. i think that's a lot more financial hurt than buying new tires. (and i would be surprised if the damage caused by mismatched tires was covered under warranty.)

your choices would seem to be either 1 new tire shaved to match, or 4 new tires. and the math is pretty $traightforward.