When I was looking at tires for my Camaro, I made a cardboard template with the correct backspacing I needed and checked for fit at every angle I could. You'll have to convert metric to standard 25.4mm = 1" so a
275/60/15 comes out to be approx 28" tall x 10.8"wide.
275/25.4 = 10.8 wide
10.8 x
.6= 6.49
6.49 x 2 = 13.0
13.0 +
15 = 28 tall
*275 is mm wide (overall)
*60 is aspect (sidewall, one side) need to times by 2 for top and bottom of tire ( the .6 above) if it was a 50 it would be .5, if it was a 45 it would be .45, get the picture ?
*15 is the wheel diameter, so add 15, if it's a 16,17,18, ect, then add that number.
Good luck !

click to enlarge.