Does even a small spare tire difference matter. In my case the spare is 255/70R18 (new, never used) and the other four are 265/70R18. In real size this would be 0.5" smaller diameter and 1.7" smaller circumference. This seems like it won't hurt for a short trip home or the tire shop. And if I understand this, if in 2WD the front would be 100% safe for a smaller spare?

 

Thanks for the info. Excuse the ignorance of the specifics on our differentials I'm still learning. The difference is a 35 to a 37. So from what I read would it be ok if it was taken out of 4wd and the smaller spare was run in the front only? I'm saying just to get home. Or would you still ruin something.

 

On a non-drive wheel, up front, it would be ok to limp home, unless you had to slam on the brakes, and your ABS and stability control, etc, went crazy trying to figure out why your steering angle said you wanted to go straight, but you were obviously turning towards the side the larger tire was on (As the smaller tire would tell the computer that it was going faster/was the tire on the outside tack in a turn, etc...)

Similarly, in an emergency maneuver, the difference in steering input and tire speed signals would make the jeep think your were on ice or something, and it would kick in measures to keep you from spinning out, etc.

So, if you were careful, you could probably limp home, but there could be drama.



Again, I think OFF road would be MY largest concern.

If the terrain killed your GOOD 37" tire....will your crappy spare be able to get you back out off the trail that killed the GOOD TIRE?

As off road you DO need all 4 wheels to be driven, you do not have the option of not using the spare on a drive wheel...and your traction control will also be confused by the little tire "slipping" as per the computer's signal that its going faster than the other tires, etc....and it may be trying to apply the brakes to it, to slow it down to the speed of the other tires, etc....making it sort of drag you down/resist the propulsion of the other 3 tires, etc.

Airing the others down enough to make all 4 the same diameter works from a diameter stand point, but, if the terrain was such that you would want a particular PSI to handle it, are you able to get through it aired down more, despite the loss in ground clearance, approach and departure angles, etc?

If so, did you really even NEED 37's in the first place?

 

Not to mention, same size spare will allow a 5 tire rotation, and increase the milage you get out of your tires

 

X2 on the increased milage with the 5 tire rotation

 

So what method of five tire rotation have you guys been doing?

 

I do the rearward cross: