Thanks - I just noticed that Excap uses 20" rims on their upgraded Steyrs (http://www.excap.de/upgrades/reifen-r20).The only singles that you are likely to find on the shelf at truck tyre places in Europe are 385/65 on 22.5 inch wheels, as these are commonly used on the steer axle of heavy trucks. I suspect that the same is true in the US, although I saw lots cement trucks with huge 22.5 tires (425 or 445 wide). I don't know if the load capacity of the 385s is enough for the back axle of your truck, you'd need to check.
20 inch wheels are not a common size anymore outside of military and specialist trucks, and so getting tyres is likely to require ordering them in, wherever you are. They come in a better choice of off-road treads, and if you want tall rubber, there's not much bigger than the 16r20 XZLs.
Thanks Neil for your effort.Peter
Sorry not sure what ET Stands for.
I have the same rims front and rear and this is the number stamped on them if it helps
2228 22.5x11.75H 12-03 T
Thx, seems like the wide 425/65-22.5 on a 13" wide rim would be the best choice then, as I eventually I will end up in the dunes in Western Sahara/Morocco.I have 315/80 22,5 's on our truck. Great road tire but stay clear of the soft stuff they are not wide enough. After all the wear issues friends with 20" rims and tires 22.5's are the way to go, but I would go with a minimum 385, preferably 415. These widths are standard dump truck tires.