Originally Posted by Gav Diamond

I can fit 245.40.17 or 235.40.18 on rear of mine with no issues.
If you have not trimmed the metal you are limited to either 235.40.17 or 245.35.17 but this is normal road tyres.

This is all if you are on a standard beam, if you have a 6 degree beam this will cause more issues as the standard beam causes camber when the wheel goes up so the top of the whell/tyre goes inwards at the top, if you have 6 degree beam the wheel/tyre stays level so you may have to step down on tyre width or cut the metal lip off the arch.

On my rear arches I have no lip at all anymore and the kit is bonded on.
I still have to mod my front arches as the bodyshop forgot however I have spaced the front of my wings out but with the saff roll bar and 215.40.17 tyres I had to trim the front bumper and splitter.
I may fit compression struts though and will set the wheels in a mid point from the standard roll bar and the saff roll bar.

Hope this is of some help