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Drivetrain vibration on 2008 subaru outback

How much difference between front & rear tires will cause a problem?

I have a 2008 Subaru Outback 2.5i,5spd manual, with @17,000 miles. After the roads cleared up this spring we noticed a vibration in the drivetrain(very noticeable above @55mph). The rear tires were worn more than the front (very even wear) so I had it aligned, and had the wheels balanced. It rides better but the vibration is still there. The front tires have @8mm tread depth & the rear @5mm. Could this amount of difference between the front & rear tires set up a vibration in the drivetrain??

First thing is your car is under warranty so use the dealer. I believe they do one alignment within the first 3yrs/36k if a noticable issue.

3mm is about 1/8" is really negligible. Make sure tire pressure are set correctly, don’t trust tire place. Use the placard for pressures on inside of drivers door jamb.

For your next oil change go to the dealer and have them check the issue(under warranty). Make sure to produce documenation of alignment/rotations.

It could simply be an out of round tire. Unfortunately in that case a good dealer will work with you otherwise you may have to visit a Bridgestone tire dealer(if installed brand).

That much difference in tire wear from front to back indicates that the tires were not rotated as specified in the manufacturer’s maintenance schedule. The reason for tire rotation on an AWD car like the Subaru is to prevent damage to the AWD system.

Whether this relatively small difference in tire circumference would damage the AWD system is hard to say, and would probably depend on how long the car has been driven in this condition. If the car has been driven in this condition for hundreds of miles or more, then it is very possible that damage has been done. The AWD system on manual transmission Subarus is less prone to damage than the AWD system on most automatic transmission Subarus, but…

I agree that the car should be taken to the dealership, but don’t be surprised if the warranty on the AWD system is now void, due to failure to rotate the tires.