Okay guys so I have the stock 15 inch wheels that came with my XJ and I also have a set of 2012 JK Rubicon 17 inch wheels and. 4" lift installed. Question is now that it's time for me to buy good MT tires which rims should I buy tires for 15's or17's? I will be purchasing a 32ish" tire And didn't know if it would benefit me to purchase that size tire for one wheel diameter or the other...
If it matters I'm looking at either the goodyear MTR or the BFG mud terrain that came stock on the Rubi.

Sell the 17's and buy some 15" steel wheels. Tires for those 17's would be outrageously expensive and the backspacing on them suck..

Sell both, buy some 15x8's with 3.75-4" backspacing.

If it's street driven the 17s will ride better but if you plan on going offroad the 15s will ride better and you can air them down. You can air down a 17 but not nearly as much and you have a good bit less sidewall to flex.

you have the same PSI regardless of your rim size... 32s on a 17 isnt like you have no sidewall. larger wheels will perform better on and off road... less rubber to wobble around.

You can air down a tire on a 15" rim the same as a 17 but to get the same result you'd need to go much lower with the 17 since it'll have less sidewall and a thicker one as well. And the sidewall flex makes a huge difference in rocks and rough trails. That inch of sidewall missing in the 17 would make a difference. Petersons did an article several years back and found a 35 on a 15 has the same amount of sidewall flex as a 38 on a 16. That sidewall flex equals traction in loose and rocky terrain.

eh, i dont really think so. i'd rather have my 35s on 17s than 15s. my buddy's rig on 40s on 20" wheels does great. a 40" tire on a 15" wheel is just ridiculous..... you dont even need springs at that point.

i believe the 17's are going to need an adapter to fit your xj also

Yes adaptor need. Add up the cost of the tires for 17s and the lug change adapyers you will see you could get new 15" crager rims and the tires you wanted.

It's a no brainier , 17s for sure. Will look and ride better on road , and will make so little difference off road it not worth worrying about. Do you think you will ever get stuck and say to yourself , I would have made it through on the 15s. Probably not.

Adding spacers, yuk. If you had a set of 17"s with proper backspacing...

17, I scored the same set of 5 for $100, they were take offs, the adapters aren't that expensive, and if you get 1.25" or more, the backspacing of those new 17's will be more than the stock 15's. Do the math, and look it up. http://www.ebay.com/itm/360654649849...84.m1423.l2649

17 in MT 32" In about two weeks I'll be running these, with those 17's and the adapters. Good luck!

The added sidewall height will help the tire form around rocks when aired down and wheeling. that wont happen with a 17 inch wheel and a 32 inch tire.
go with the 15s. Only time a 17 is a good idea is with a larger tire, like 37 inch or larger.

the taller side wall will soak up the annoying little bumps like washboards and small stuff your suspension is still too stiff for, thats why i like my 39.5s on a 16.5 inch wheel it feels like you're riding on a cloud with 2-3 psi in the tires

my only comment on this is that 15's are slowly being phased out and less and less tire sizes are being available as time goes on for the 15" rim

This.