was wondering if anyone has gone from a 15 in wheel to a 17 or 18 without any problems? Or is that a waste of time to gain an inch?

 

Depends on what your goal is by going up in wheel size.

 

just a way to gain more clearance is my goal. I just want to do trails and mudding. wanted to go with a 2 or 3 inch lift and 31s as I will be driving daily as well.

 

You can easily get a 31" tire on the 15" rim - 31x10.5R15 is just one option.

A 2" Budget boost should give you enough clearance for the 31's without rubbing. Just make sure your springs are not too saggy - on a 20+ year old truck you might end up needing to replace some or all of them.
If you go over 2" you will need to consider a lot of suspension/drive-line mods in order to get a decent ride as a Daily Driver.

 

Changing the wheel size will not change ground clearance necessarily. Changing tire size will change the clearance. You can run a variety of tire sizes on any of those wheel sizes you mentioned.

15" is very common for older XJs and is typically going to be used with a 235/75/r15 or 30x9.5/r15 or 31x10.5/r15 tire. There are plenty of good all terrain and mud terrain tires that still have sizes for a 15" wheel. However, more and more, tire manufacturers are moving away from 15" sizes. But good tire options will remain for 15" wheels for quite some time - especially for tires that are targeted at the 4x4 off road market. Many many tires still come in a 235/75/r15 size option. Which is a good fit for an XJ with no lift.

If you want the most flexibility in tire sizes across the largest variety of tire manufacturers, 16" is the new normal. Having 16" wheels would give a wider selection of tire sizes across a wider variety of tire manufactures and tire models.

I run 15" wheels with a 30x9.5r15 tire with about 1.5" of lift (Dorman HD springs and air shocks in the rear with standard shackles, and a 1" spacer over the front coils in addition to the 1/4" stock rubber isolator).

 

thank you, my goal was 31s from the stock 235. maybe im looking at it wrong. I was figuring 31s on 17 inch rims would give me a little more than 31 on 15 in rims. lol did I confuse myself?

 

Yes. 31" would be the diameter of the tire, regardless of the wheel size. The difference would be that the sidewall of the tire would be a little larger on a 15" wheel vs. a 17" wheel. But the outer diameter of the tire would be the same.

 

One of the advantages, in my opinion, of the larger tire sidewall is that if you're off-roading and you scrape a rock on the side of the wheel, the larger rim is more at risk to be damaged or have a balancing weight knocked off and there's no flex/give on the metal rim whereas the rubber of the tire can flex and at least give you a chance of escaping without major damage. Also a bigger sidewall gives you more flexibility (if you have a portable compressor with you) to deflate the tires a bit to get better traction while wheeling and then inflate back to spec when you're going back on the road.
It's probably trivial though between a 15 and 16 inch rim.

Your decision should rest on what you're planning on doing. If you are buying new wheels/rims regardless, it might be better to get a 16" wheel if there are more tire options (and hence better prices) on R16 tires today and going forward. If you're looking to minimize the cost and get to 31" (and the current wheels are in good shape) then it might be best to just put 31" R15 tires on the current rims.

 

Gent should look at an online "Tyre and wheel size calculator"...this gives all the dimension combos

I have various tyres on 15" Jeep wheels, including 30 x 9.5 and 31 x 10, also 225 & 235

I also grabbed a set of 16" good-looking wheels off a Ford Explorer, around "00..they take the very common metric tyre 265/70/16, and fit the XJ wheels stud pattern

these will have A/T or highway, the 30 x 9.5 and 31 are M/T