I recently switched from 14's to 16'' irocs..b4 the swap the left rear would have a strange vibration...like blump...blump and getting more frequent as speeds picked up then subsided around 45..after the iroc swap it is doing it on the right rear..same thing..wtf?? Can anybody help...all corners have been balanced

 

I have a 1992 Firebird that had the same problem.........like a thumping sound coming from the drivers front tire when you excellerated..........found out I had a bent rim on my car....replaced the rim and no more problems...........