[bobv]

All tires front and rear tend to cup due to braking. The rear tires however will wear more evenly because they have rotational force in both directions, they brake and drive which evens out the wear. You will see cupped front tires a lot on motorcycles because of this uneven wear and the fact they are not rotated front to rear. You wouldn't have your car set up with more braking in the front rather than the rear? That could make the cupping more pronounced. As mentioned tire rotation would even out the wear.