Dually Tires - How Big?

[Tance]

I’m restoring a 1984 K30 one ton (ex-military M1028A3 dually). It had Buckshot 305/70R16s (33s) when I bought it, they look like one huge tire in the back because there’s no gap between them… I know, everyone says bad news… rubbing, heat, blowout, etc. But they must be a pefect fit because after disassembly there’s not so much as a smudge on the sidewalls… and I was goosnecking a 30 ft 5th wheel so they were loaded.

Anyway I’d like to go with bigger tires, probably 35s or 37s. So my question is… what’s the biggest tire size I can run on a dually? I’m guessing the answer is as big as I want, as long as I use a spacer to keep them apart.

So assuming I get fender clearance with a lift, then dually tire size would be limited by wheel width… up to 35s on a stock 6-7” rim, 37s (and up) on a 10’ rim… correct?

As for width... 12” wide no spacer… 12.5” or wider, need spacer, correct?

Thanks!