So.... here's a little lesson on tire size identification. It always confuses me when people say 50 series or 60 series are larger/smaller and will this or that work, so here goes...
When figuring the size of a tire you must first be able to "read" the size that is printed on the tire! In your case you would read it as follows....
275= the width of the tread in millimeters, or in this case 275mm
50= the height of the sidewall of the tire in relation to the width of the tread as figured in percentage... in your case the sidewall height from the road to the rim is 50% of 275mm
"R"= radial
"15"= the rim diameter
So, when going to a "smaller" tire, when you say you're going to a 265 or 255, what you are really saying is that you are going to a narrower tire! When you say you are going to a "60"'series tire, what you are really saying is that you are going to a taller tire!! Make sense??
You need to accurately assess the wheel opening and measure your tire requirements within the confines of your wheel opening! Remember that no A body ever came with a 15" rim, or anything close to a tire that is 275mm wide.'you are fighting a losing battle guessing about tire size, and more so when you are fighting against a tire and rim that is obviously too big for its intended use!!
Can you rework this problem?? Of course!! But you need to go about it armed with the correct information, and apply that info properly!! Geof