I agree with RapidRobert, those tires are too wide. BFG says for a 255/60 the wheel width should be 7"-9" and for 275/60 7.5"-9.5". The chart below shows a 225 being the largest 60 series for a 6" wheel.

http://www.bfgoodrichtires.ca/tire-selector/name/radial-t-a-tires#techspecs