18" spare?

[Scott4957]

Guess I never bothered to check until now. If we can't mismatch tire size by more than 3% then why can I run on an 18" spare? I assume for a very limited distance?

[sholxgt]

Hmm.  The maximum variance is for the sake of the PTU.  We don't have a limited slip diff front or rear to consider, so as long as one of the tires is within tolerance, maybe it's ok?

[Scott4957]

I guess I didn't think about that. I think the issue would come with two different sets different from front to back?

[derfdog15]

Its not the diameter of the rim, its the size of the tire (height is more important I believe?). SO if the spare is the same height or within the tolerance I think that is what makes it work.

[sholxgt]

Its not the diameter of the rim, its the size of the tire (height is more important I believe?). SO if the spare is the same height or within the tolerance I think that is what makes it work.

Yes, but in this case, they are way, way off.

145/70-18 vs 245/45-20 = over 10% variance

I think it's ok as long as you don't mount two spares on the same axle.  LOL