A friend of mine is planning to put 6 inch steel rims on his Mk2 and was asking about tyre sizes (thinking I had had wider rims on my car). He wants a lower profile as he has overdrive and a 3.59? diff. So my question is has anyone any experience of wider tyres on a Mk2? How wide and low can you go?

5.5 is about it.
Modify the spats and you can go biger, but make sure you clear everything on the back side (caliper lines, ball joints, tie rod ends, that silly stuff).
I read up on it once, can't recall what you need to do.
Suffice it to say, my MK2 was making a funny rattle in the LF, found one of the caliper connector lines was just not quite flush against the caliper body and hitting the center section.

I've got 6" Minilites (Mags) on my Mk2 with 205 70 15 Avon CR6ZZ tyres. You need to put thinner spats on the back but otherwise no problems or modifictions needed.

Thanks, that's just what I wanted to know!