Currently, on my 1275cc Mini-engined NCF Blitz2 I'm running 13" Wellers, with 205/60/13's on for all-round use, even though they are a road-type tread, they perform quite well off-road, as long as the gtound isn't wet, or slippery.
I have a set of 12" Hillman Imp steel wheels that I'm going to try with some 155/70/12 grasstrack/mud+snow tyres, (although they may look a bit skinny!
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....but just today, I found a supplier of 6ply radial ATV tyres, 25x8x12, and 25x10x12, road legal and E marked for road use, but with a nice chunky off-road/all-terrain tread pattern, at £58 each, I called the supplier and he reckons they'd be more than up to the job of carrying my 650kg Blitz2.
My current tyres are approx 21" overall dia, these ATV ones will be approx 25", so a bit more ground clearance, and slightly taller gearing, but being on 12" wheels, they'll look nice and fat, and add a little bit of 'give' to the hard, rubber-cone mini suspension on the back of my buggy. The supplier tells me that they will go on a standard 5.5J Imp wheel, or I could get the Imp wheels banded to make them 6, 7, 8, or even 10" wide, to get maximum benefit from them, but probably not wise to go wider than 8" on the front as steering effort will increase. I'm thinking 7" wide and fit the 25x8's on the front and back.
My final drive at the moment is a 2.95:1, but I have a 3.44:1 diff and box waiting to be fitted, it'll be interesting to see what difference they'll make to performance. (current max speed on the 205/13's at moment is 95mph*, but won't rev out in top, 1st final drive was a 3.195:1, and I got 100mph*, on 185/60/13's,... I'm guessing it should rev-out in top, and have a slightly higher top speed, with acceleration the same or marginally better due to narrower tyres?
-Incedently, talking of banded steel wheels, I've just had a set of Fiat Seicento 13" steel wheels banded from 5" to 7.5", to go on my mates Fiat-engined KR3, although they still need powder-coating they really are top quality, and were done by a coded/certificated welder, and look as if they were made that way from new, and are guaranteed not to collapse or leak in normal use, ie on a car, so on a buggy weigh 1/2 to 2/3rds the weight of the car should be nigh on indestructable. We are going to fit 185/60/13 Gravel/Forest/Mud+Snow tyres to them, so there may be a little 'stretch' on the sidewalls, but this should only accentuate the 'deep-dish' look even more... as soon as I can, I'll post some pictures up!
(*All speeds were measured using a sat-nav, whilst driving on a private road, officer...)