i have a 69 chevelle with a 12 bolt posi limited slip rear.does the spare tire have to be the same height as my rear tires?both are 15 in rims,my spare is smaller will that be ok?thanks

NO! You must have the exact same size (heighth)wheel or you will burn up your posi unit, at least that's what I've always been told, I'm sure somebody will correct me if I'm wrong.......KZ

thanks KZ, I appricate your good advice.Ricky

It will burn it up. It almost simulates a wheel spin and tries to lock up, and when it does you have one end trying to go faster that the other and you end up trashing the rear clutches. Same would happen on a locked rear. Two tire sizes = two speeds = no good.

I agree with you guys- different tire size= bad!!
But how long would it take to hurt something? this is assuming the sizes were close.
Andy