I was watching Hot Rod TV,,,,on the tech section, they mentioned not to run a space saver size tire on a car that has a posi-trac rear end,,,,,said the posi unit will go bad in 10 miles!! OK---I have 27" tires on my posi-trac chevelle,,but my spare tire is only 25" tall,,,would this screw up the posi unit if I had to use it on the rear of the car and drive the car for a distance?????

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ACES #3355
ChevyTalk Silver Member
Metroplex Muscle Car Club
Assoc. of Proud SS Clone Owners
1972 Chevelle SS (clone),black/black 350ci

Right.

The suggestion was to use the space saver to get off the highway where you could do a swap and move the spacesaver to the front and a front to the rear (if your fronts and rears are the same size) or swap both fronts to the rear and the good rear and the spacesaver to the front (if you're "big and little").

When you drive with the posi and differing height tires like that, you end up with it trying to drive the rear axles at the same (rotation) speed when they really need to be going at different speeds due to the tire height.

Now admittedly, I don't actually own a car with posi, so all this is from what I've gathered reading/watching/asking.. so I might have understood wrong. Better safe than sorry in this case though.