So, I went and bought 235/85R16 tyres for my P38 after reading this sticky and went for some serious green laning at the beginning of this month. I'll post another thread to share the story but thus far I have the following experiences.

the tl;dr version: won't fit without modification.

Tyres: 235/85R16 Goodyear wrangler MT/R with kevlar
Wheels: terrafirma anthracite wheels with beadlocks (partnumber TF107)

First of, the I am not sure what the ET value or ofset of these wheels is but I suspect they are somewhat different from the stock wheels, ie. they stick out. With the much larger tyres they do tend to hit the wheel arches sooner. The beadlocks I beleive make the tyre stick out even further adding to the problems.

In short: the wheels scrub A LOT. I added 5mm padding to the front and rear axle, just testing stationary if it would prevent the wheels from touching. It did, but when the car was laden in highwaymode I would hear the tyres scrub on the larger bumps in the road but I managed to do 500+k's without too much trouble. During heavy articulation things were doing well except for the rear left. In future I think I'm going to have to adjust the bump stops further. Also these bump stops are old and probably deform to much. Polyurethane stops and a slightly thicker packing (say 1cm) will probably suffice.

As far as the tyres go, I absolutely loved them! I did schred one when hitting a submersed concrete plate with 80km/h but I guess no tyre would have survived that. They ride pretty comfortable for a muddy compared to my mates cooper SST's. My theory is that the asymmetric design whicfh is primarily to clean mud more easily also add's (positively) to the road behaviour. Have not tried airing them down since I do not yet have a compressor to reinflate them (well the car has one, but not hose yet :P)

Regarding the wheels: they look the part, seem decent (they are actually italian built, there is a brand in them I'll make pics later) but installing beadlocks is a b*tch. 24 or 26 nuts that you have to cross bolt and re-torque at least a dozen times. 5 wheels took me a whole day. They do take different wheel nuts and they do not come as standard anymore so do not forget to order a set! After hitting that concrete slab which ruined a tyre the wheel is still in tact, not sure if lucky or just tough wheels. Impressed in any case.