I have a 93 jlx 4 door and I have some 29-12.5 trencher tires for it. Well the tires need 15x10 rims. I have been looking all over and Im worried that Ill get the wrong back spacing. What backspacing should I run with these tires. 4" seems to be the norm.

I had the same ? about the wheels a few months ago, so I called a local tire shop and was told 12.5s can be mounted on 8" wheels. As far as spacers go it would depend on the offset of your wheels and how far out you want them to stick. With that wide of a tire you also need to consider the clearance in the front when turning. your tires may hit the fenders or bumper if you haven't done a lift or made body adjustments.

15x8's will be just fine. My friend ran 33x12.50's on his jeep for a long time on a 8inch wide wheel. It will actually allow you to air down a little more with less risk of breaking the bead.

I ran 15x8 wheels with 33x12.50s on a full size Bronco & never had problems. I think the 33s on my Samurai were mounted on 15x10 up front & 15x8 in the rear . Don't ask me why, I didn't do it. I currently have them sitting beside my house.

but the problem is that they are thick agricultural tires so they arent as forgiving in the flex department. well on either rims what would be my backspacing? would 4 in work?

I'd have to measure to make sure but I ran some 12.5 on a set of 10" rims with 2.5" of backspacing. it was the most you could get without going custom. I've got many sets of 4" ers but they all end up rubbing the springs.

IF you go to the 2.5 you have to remember that they love to mess with bearings....the rims are so pushed out that they creat a huge stress on the bearings and all other parts. We call them bearing breakers.

I had just gotten the safety inspection and the mechanic told me to tightened the bearing on one side. The other side was fine. On the way home the good side locked up solid and we went for a 25' skid at around 80km/h....it wasn't a fun ride.

Spend the money and get the right offset and run the 10's...you'll love them. they look great too. I've got a few set's with 2.5 and a few with 4 but shipping would be a problem.