Subaru Forester 2004 tire replacement

Ok here is the deal. On a Subaru AWD vehicle it is important that all of the tires have close to the same amount of tread on them. Reason being is a tire as the tread wears, the tires overall circumference becomes smaller. Lets say you had 3 tires with 7/32 of tread remaining versus and the forth had 12/32 the tire with 12/32 would actually spin slower than the rest. On a Subaru The TCM(transmission control module) would reconize the speed difference and think the other three tires were slipping and apply more power to the one that is spinning slower while decreasing the power to the three that were spinning quicker. But if the road conditions arent causing the difference in wheel speed readings then thats where transmission damage can occur. So a good rule of thumb is no more than 3/32 difference front to rear and no more than 2/32 side to side. As far as the potential for damage it just depends on how much difference there was between the tire you replaced and the other ones on the vehicle.I hope that helps you.