I know from running tires from Super Swamper they will suggest the rim size for the tire. Running a tire too wide/narrow for your rim size will cause the tire to wear improperly, but if that isnt a concern you usually <from my experience> can run what ever fits. I'm currently running a 19.5" wide tire on a 15x10 rim with Zero problems. Im able to run a low air pressure without problems<yet>