Why is there always such a debate regarding tire sizes? Some people say a 31" tire will fit a stock ZJ while others say a 31" will NOT fit a ZJ w/ UC and BB. Are ZJ's that different? I would love to get a 31 for my ZJ w/ BB and UC but am afraid it would not fit.

I have two ZJ's and a Wrangler. One Zj in very modified and one is slightly. The slightly I have no UC and a BB. I run 31's with very minor front fender trim. A little plastic where it touched.

Bottom line if you wan't 31's put them on and don't be afraid to trim a little. You can't tell by looking.

You can sit back and speculate all year, but the 31's are still not on your ZJ. The only way to find out if the UC and BB will fit is try it.

Go for it :cool:

I have a Tera BB and Up-Country coils, and my 31" BFGs don't rub.

I have Anthony's BB and non up country and I only rub at full steering lock. I ran swampers for a while and same thing.
The swampers were 31.3" my BFG's are around 30.6. I hope this helps you. Go for some 31's you'll be happy.
:ZJ:

Back in the day I ran 31x10.5 bfg at's slightly worn with no lift, non U/c. I had to trim the bumper a little and a few places inside teh fenderwell.

In any case with a BB your 31" tire is traveling in the same arc as it would be without a lift. So if you have a BB and trim to get no rubbing even at full flex, full lock, you will have trimmed enough to run those tires with no lift.
-Nate

There really is no debate. It all depends on how much your stocker is sagging, how much your willing to trim if any, how much rubbing is tollerable, and the actual hight of the tire. For example 31" swampers will likley rip something off of a stock rig, as the measure around 32" new.
Jereme

I'd suggest that it has more to do with backspacing being left out of the equation. The 31 is a 31 is a 31 arguement doesn't work when you're talking about stock wheels' backspacing compared to aftermarket. Stockers will invariably leave your tires closer to the insides of the fenderwells, thus rubbing under turning and flexing circumstances. The correct b.s. is necessary in order to make ANY tire work correctly under flexy situations.

With the correct backspacing, a true 31"x10.5" tires will indeed fit the ZJ with the steering stops turned in correctly. Correct backspacing for the ZJ seems to be somewhere between 3.5"~4.5", depending on who you ask. Stock wheels have as much as 5.25" of b.s..

Mark Smith, the guy who runs the Jeep Jamboree Rubicon Run, has had this to say about these tire sizes.
"On my own Grand Cherokee, I use Goodyear's Wrangler radial AT tire in 30x9.50R15, a mud & snow tire with load range "C".
"You can, on a Grand Cherokee, Cherokee, or the new TJs, put on a 30x9.5 or a 31x10.50 without a lift kit. It will bind a little bit in a tight turn, but other than that they work well, and they do give you just a little bit more clearance."

193 'views' and only 7 replies .. hmmmm

I disagree with Kevin :spank:

I run a 31x10.50 which runs about 30.7" OD. On a stock XJ 15x7 wheel with 5.25" backspace. I initially ran these with NO bumpstop extension, and they stuffed. Rubbed in places, caught the fender lip a bit when turning .. but only at full compression. I do have 2 washers under the steer stops, and sometimes I still hear them catch the LCAs. But at least they fit up inside the fender lip. If I had less backspacing, they would stick out an extra 3/4" and I would not get the compression that I have.

Here's a link to one of my pics. Its a little big to show in-line, but not entirely dial-up unfriendly.
http://www.zjilla.com/temp/GM5.jpg

With less backspacing, and the tire ticking out further, I don't feel I could have gotten the tire this stuffed and still been able to turn the wheels.

Most people ask 'what is the biggest tire I can fit w/o rubbing. Which is a 30x9.50. If you are prepared to trim a bit, or tolerate some rubbing, and shim the steer stops, then there is really nothing wrong with a 31x10.50. Even with stock 15x7 wheels. My suspension doesn't compress any further than stock, and I run successfully. with attention to detail .. its all in the details.