900R22.5 is approximately 38-3/8" height, 255/80R22.5 are 38-1/2" in height. About two inches taller than the 8.25-20s our rigs were always upgraded to versus the 7.50-20s Chevy put on in 1965. The extra height of the 22.5" solutions nets about 150 engine RPM less at highway speed. Not a huge difference, but not nothin' either. Right now I gotta spin the big Cadillac V8 at 3800RPM to go 65 miles an hour. After the taller tires and the 5.57:1 gear set I was lucky enough to find, that'll be down around 3200 which is just right for the 500. Will probably net me a mile or two to the gallon also, when I want to get somewhere at faster than 54mph.
The only downside to 900R22.5 or even moreso the 255/80R22.5, is both sizes are uncommon-the 255 size most so as it's only made by Michelin and each new one is around $800. I was patient enough to find all six for $100 apiece used, with reasonably modern date codes, lots of tread, no cracks or repairs.
Most 19.5" tires seem to top out around 34" in height, so on a two ton, that's gonna gear you pretty short.
