How far can I drive on my stock 255 70 17 spare if I have 285 70 17 onthe other three wheels. Will it screw up my diff. or transfer case?

 

As long as you are staying with the 17 then you will have no problems. The problems happen when you say use a 17 spare with three 20's. Short trips are less of a problem than long ones. I replaced my 18 spare with the correct 20 to avoid any problems when I upgraded to the ROUSH 20's in case of a highway flat.

 

As long as the spare is about the same OD as the other four tires there shouldn't be any issues.

 

Yes, because the tire diameter that meets the road is different.


The 255/70's travel 97.6 inches per revolution.

The 285/70's travel 102.8 inches per revolution.

That 5.2 inch difference per tire revolution is slippage that can be hard on everything, especially 4 wheel drive, including anti-lock breaks that assume all 4 tires are the same diameter.

When I upgraded my tire size, I purchased a matching wheel and 5 new tires to have the same size spare. When rotating the tires, just do a 5 tire rotation with the spare.