My 255/60's ride on an 8'' rim so 275's should get at least 9-9.5 right...
According to the tire chart I use a 275 is ideal for an 11'' rim but will squeeze on a 9.5, the wider the rim the better your handling and even tire wear will be. A narrow rim promotes wear in the center only, unless you lower the tire air pressure but that ruins the possibility of good cornering.