10.00 X20" on 7" RIM

what size did the truck come with in the first place ??

If you do go up a larger size you will throw the gearing out and find that your always 1/2 to a hole gear out so this means the truck will screaming its tits off in top gear .

In other words the gears come to tall for the motor. Dave

on average a 10.00-20" tyre size will up your highway speed by about 5km/h over the original 900x20" size

so why not stick to 900x20 there easy to get how many does he want.

I would need 6 if I convert to 10.00's or 4 for the drive if sticking to 9.00's at the moment. I would need 6 if I go radials all round.

The reason why I was considering the 10.00's was to:
a/ pick up some top end,
b/ easier to find rear guards with the same radius and width.
The 9.00's have a wall to wall width on the duals of 22"
and the 10.00's will be alot closer to 24" if on the wider rims and 625mm on tubeless with 11R22.5.