wayne:
Do the rubber tires or foam tires have the problem? If the problem happens on rubber tires, it could be the inserts. For foam tires, perhaps your tires are too soft (track traction too high for the foam tire you chose). The tire problem may manifest on the exhaust side of the car due to more clockwise turn of the track.
Since your car does not track straight, the problem can be caused by the chassis setup, different tires used and the steering trim. Make sure on the left and right side, the droops are the same, the shock pistons, springs are the same, shock rebound degrees are close, the ride height are the same, same tires. Of course when the steering is at neutral, both front tires have the same toe in/out. Also, check the pivot balls whether they are bent.