I use radial tires because they handle better, are quieter,and give better gas mileage but I know people who have had rims crack from the stress so I check them often. The only cracks I have heard of occur around the bolt holes. Is it true that when left hand threads were used they were on the drivers side? That seems wrong to me. With knock-offs the left hand thread is on the passenger side and if you get that wrong your wheels come off.
