20. 5's? Most of the transit busses I've seen around here run 22. 5's. I used to work for a tire distrubutor and we sold lots of 20's, mostly bias ply, but I can't recall ever seeing a 20. 5.
I do think 22. 5's would look cool on a 3500, especially if you can get them aluminum, those big rims are HEAVY. Tires would probably last forever, but wet traction might leave a bit to be desired.
Pete
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'97 2500 CC 4X4 5spd Sport
'83 K5 Blazer 350 TBI (ex 6. 2), 39. 5 TSLs, 3" lift, Dana 60/GM 14 blt, Detroits