It's wondered if anyone can tell me how big a tyre I can run on stock 15" rims please ?

 

If your talking height, skies the limit. But width, if its a 7" wide wheel (most stock xj wheels) then i wouldn't go more than 10.5" on the tire.

 

30x9.50x15 is the biggest tire I have ran on my stock 1990 xj with no problems

 

I have 31x10.50x15 with stock height and they rub a little above the coil in the front

 

stock height, you can go about 30" without some cutting
on a stock 15x7 rim you can only go about 12.5 wide but it will rub without the proper backspacing
on a stock 15x7 rim you can go as high as you want, 44s & higher even
ive seen 44x18.5 on 15s but they were 10 wide

you can put on just about any size you want on any vehicle on just about any rim - its just a matter of whats going to be safer

stock height stick to 30x9.5
3" lift can go up to 31 without trimming 33s with minor trim
stock 15x7 5 - 5.5 bs rim 9.5-
you can do 10.5 if you can find the right back spacing
15x8 you can go 10.5 with 4.5bs
12.5 if you can get 3.5 - 4.5 will rub

 

your 15x7" rim came with a 215 or 225/75r15 from jeep.
you can run a 12.50 (i think.. it would not be my recommendation, either way) on a 7" rim, but a 10.50 is better. (still maxing out a 7" rim)
at least get a 15x8" (or 15x10", but this doesnt give you an option to run a smaller (stock sized) tire.
i have 235/75's and there is no fender trim and minimal rub (mostly cause no front sway bar...) look at my pics (or just the avitar) to see what 235's on a 2" BB at full flex looks like...
you can run a 31x10.50 with no trim if you bump stop properly!

look at N2O's thread "LOW COG suspension tips/tricks" seriously!!

 

no wider than 10.50