Originally, the plan was to get bog-standard super single tyres which are 386/65R22.5. Unfortunately the load rating of these tyres was less than the rear axle rating by a few hundred Kgs, which meant that technically the truck could have been defected.
The solution - go up a size to get a higher rated tyre. We ended up with 425/65R22.5 tyres, a most uncommon size (here in Australia at least). These things are HUGE and as heavy as. This is a size comparison to my 8' x 5' trailer fitted with 4x4 tyres:
There's not a lot of choice in this tyre size. It was either Bridgestone M748 or a Chinese brand that I can't quite remember now, but something like Golden Crown Chain brand. Needless to say, I went Bridgestones, and got 6 shipped down from Brisbane to Adelaide. 5 to go on the rims and one to have as a tyre only spare (which will probably sit on the roofracks).
This is the first test fit, with the rims still only tack welded:
The combined weight of the rim and the tyre is something like 120Kg, so way too heavy for me to pick up. Just the tyre on its own is over 75Kg. Will need to build some sort of winching system to get the spare in and out of the garage area. I did think about slinging the spare under the rear chassis overhang, but they are such wide tyres that the departure angle was ruined.
This is how it looks with the rims painted white:
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