by Yuri4x4 » Sun Oct 31, 2010 9:06 am
For the Jeep:
It also depends if you have lockers... If your diffs are open, than you would be alright running one smaller tire on the Jeep, on the road (2wd). You shouldn't run in 4wd like this tho. (But, if it's not too large a difference, you could 'limp off the trail'.)
That being said: your Wrangler Unlimited probably has a rear Dana44 and Trac-loc (limited slip) at the least... So I would say you need a spare tire the same circumference (or close) to the Jeep's size. If you don't want to have a full-size spare, than you will need to make sure the spare goes on the front axle, without the locker/LSD. I've seen people 'get home' like this.
Also: Up to 06, you could get away with a 15" rim... 07 and above, you'ld probably need at least a 16" rim or larger to clear the brake calipers.
Running a full-size spare for the Jeep is the best way to go. It doesn't have to match the same tread/width/rim size, but it does have to be close to the same circumference. If we're only talking about an inch difference in the height, I would make sure the smaller tire is aired-up a little higher than the others and call it good.
For the trailer:
As long as you have clearance for the 33" tire on the trailer, you should be fine. The bad part about Jeep wheels is they tend to be off-set pretty far inward. (5.5" for stock 8" TJ wheels). Aftermarket rims are normally less by an inch or two, which sticks the wheel further out from the body. But if you have stockers on the trailer and it works, than an aftermarket rim from the Jeep should stick out far enough to clear the frame.