The 60's and 70's you are referring to is the aspect ratio. It has nothing to do with the width of the tire, but it has everthing to do with the height. You are using both interchangably. I am not fully understanding what it is you are after, but.... If you like the width of the current tire, but want a shorter tire, a 255/60/15 will give you that.
Example: (number will be approximate)
255/70/15 = 10.00" Wide with a 7" sidewall yeilding a 29" tall tire.
255/60/15 = 10.00" Wide with a 6" sidewall yeilding a 27" tall tire.
To calculate. Take the section width (255mm) divide by 25.4 (metric conversion to inch factor) this gives you width in inches. Multiply that times the aspect ratio and this gives you the sidewall height. Multiply times 2 and add the rim diameter and that gives you the overall height.
255 / 25.4 = 10.02"
10.02" x .6 = 6.01"
6.01" x 2 = 12.02"
12.02" + 15" = 27.02"
Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project