I have access to 255/70R22.5 tires. My bus currently has 315 80R 22.5
I don't know anything about tire sizes
Dave
Type your numbers into this, and make up your own mind. http://tire-size-conversion.com/tire-size-comparison/ (http://tire-size-conversion.com/tire-size-comparison/)
Basically, almost 15% difference in speed at a given RPM. Load capacity is 5510 at 120 psi for the 255/70R and 8820 for the 315/80R, based on singles. About 40% less. It all boils down to what your weights are. Basically, the small tire is for little Class A RV,s and big Class C's, not really for buses.
Brian
The 255/70R-22.5 is a very low profile tire aimed at electronic trailers, low boy trailers, etc. It is rated at 5500lbs per single or 5000lbs on duals. If you put them on, you'll have a real low rider bus that won't be able to get in and out of driveways, but will look cool! Good Luck, TomC