Different Tire Sizes = Differential Problems?

I went into Pep-Boys for an alignment and they saw that I had two different tire sizes on the back. I had to replace a differential a couple of months back. I had all 4 tires replaced at Discount Tire at the same time. Could the tire size difference cause the diff to go bad?|||Yep, the differential is a set of gears in the rear-end that is designed to allow the wheels on the rear-end to turn at different speeds when cornering. When going straight these gears are basically not being used. When you use tires with different circumferences you basically place the gears under the stress that they see when they turn all of the time. This creates more heat in the differential which wears out the fluid and causes the differential to prematurely fail. I would go back to discount tire and talk to them about it. They are the ones that should have to pay your repair bills because they are the ones that screwed up the tires which screwed up your differential.|||Depends on how big the circumference difference is, it should tell you in the manual how much is allowed, some cars are very sensitive to this, like subarus are very sensitive and shouldn't have more than 3% difference in circumfearance... If it's a rear wheeldrive car have them measure all 4 tires and pair up the closets matching once on the rear, or just get a new set of tires.|||The gears in the differential compensate for further distance being traveled by one wheel when turning corners and the ratios are based on two wheels with the same diameter. Using different size tires would indeed place undo stress on the gear system and could lead to failure.|||Oh yes it could!|||yes