Originally Posted by mmm def
'What if you run a 17" and an 18" on the drive wheels? Can that mess up the dif/tranny??
If you match the total circumference (wheel+tire) to 2% or under, you are fine for a spare tire that is temporary.
In this case a 17 inch wheel with a height of 45 is very close to equal an 18 with a height of 40. See the circumference calc I posted a link to.
If I had a flat on mine I would be running a 19 for 3 and 17 for one wheel, but because the circumference is close and the use is temporary it works for a spare tire.