When I bought my Umm it had ‘all terrains” fitted but these just weren’t meaty enough for offroad use..
I found that Maxxis Buckshot Mudders in size 235/85r16 fit and are very good in the mud and not so bad on the road (they seem better than the more road biased all terrains I had on before!)
– my springs are a bit tired though so the tyres just rub the rear plastic trim when at full axle articulation. They don’t catch the front springs on full lock either.
I got them from a tyre shop running out of a garden centre in the midlands – I found this company via ebay – just look up maxxis buckshot. Although this size wasn’t listed I contacted the chap and he had them delivered to me next day! The service was outstanding – they really did arrive the next morning and the price was even better just over a hundred pounds each, my local tyre shop charging me twenty pounds to fit and balance them.
nb. I am more careful going through speed cameras and watching the speed around town as I think the speedo is now showing a lower reading now the tyres are larger!