Tire sizes and diffs
 

I am hoping to get some advice from someone more knowledgeable about differentials. I've only had my truck a few months, '06 2500 4x4, and noticed my spare is a different size than the other 4 tires. It came with 275/70R18's but the spare is a 265/70R17. From what I've found on the web, the 18" tires are about 33.5" in diameter and the spare is only about 32".

A 285/70R17 is supposed to be 33" in dia., so I can get close to the size of the other tires without having to buy another wheel, so my question is how much difference is OK to run on the same axle and not hurt the diff and/or transfer case?

You can run it on the front but it would not be a good idea on the rear if you have a LS. A 275/70/17 will be close and can probably do it but in the end just buy another rim and tire. Rebuilding parts for these trucks is expensive, more so than another tire and wheel.

I am in the same boat, tried to match up a 17" to the 20's I have and nothing really comes close enough.

Thanks. I can get close, but was wondering if there was anyone who knew how close is close enough. With some of the deep tread off road tires, it seems to me that it would be easy to have one tire worn more than another and wind up on the same axle with quite a bit of variation in size. For that matter, even a large difference in tire pressure could do the same thing. So that's why I'm wondering is 1/2" is too much difference if you had to go quite a distance before getting the flat repaired. I've been in places where it's 100 miles or more to any shop.

1/2 inch is to much on an LS, on the front no problem other than possibly some weird driving. You well see very little difference in tire height from air or wear as long as the tire is the same size and brand. Mix different brands an all bets are off just like sizes.

Tire rotation takes care of wear differences.

I would agree with Cerb the best way is the same tire/wheel you are running on the rest of the truck.
If you can get a 33 inch tire and the others are 33.5 the difference to the center is 1/4 inch. if the others tires are worn some it would get you to the tire place in a pinch. I am Not recommending running different size tires on a LS but only in an emergency might be ok.

I guess the best thing would be to make sure the rear always has same tires. If there's a flat on the rear, move a front tire to the rear and put the spare on the front til I can get the flat fixed. In the future I may want to go to oversized tires, so I don't want to get a different wheel for the spare until I know for sure what I'll have for the long term.