I run 225x45-17's all the way around. My spare is a 185x70-14. The OD of the 225x45= 25 inches and the 185x70=24.2 inches.. If I had to use that spare due to a flat, would it screw up my rear? I have a posi with a Richmond racheting locker posi unit.. The closer size would be a 185x74-14, thats 24.9 inches.. What wouod you do?

 

Just to be safe, I would get a 17" spare. You don't want that posi pulling against itself.

 

it is all up to you, I have a 245/45-17 as a spare, but that is to fit around my brakes, a 185x74-14 would work fine, but you can have fun with a spare tire if you show the car...