Originally Posted by Dudesky_E36
Maybe the new rear tires just need a break in period. Sometimes they need to soften up a little, or wear away the outer surface of the tread to acheive their rated traction. Best way to do this is to rotate them to the front so they wear faster. Hopefully they didn't sell you an older set of tires where the rubber has started to harden.
or just do a couple of burnouts