sorry just my $0.02
"If it was alright to put a 275 on an 8" rim, the manufacturer would recommend it. They've obviously done testing on the effects of wide tires being mounted on narrow rims, and found it to be unsafe. If you don't believe me, go to any BIG NAME tire shop and ask them this question. Most of them won't even mount the tire for you since it would be a liability. The rim width range for each tire size that a manufacturer publishes is correct. You will always get the best ride, longest treadlife, and best traction if you mount the tire on a rim that's right in the middle of the recommended range. Personally, I think a 275 is pushing the envelope a little too far on an 8" rim, and a 285 would be just plain stupid. But hey, it's not up to me."