Hey, I was wondering how big a 315 is in inches? I have 285/75R16's now and they are about 33"s, So if you know off hand or of a chart, that would be great, thanks

 

Metric tire sizes aren't that difficult once you understand it. The first number is actually the width of the tread, the second number corresponds to a percentage of that with which equals the sidewall. And obviously the last number is the rim size, though Americanized and in inches. The last thing ya really need to know is that 25.4 mm equals one inch

So

315/75r16
315 divided by 25.4= 12.4 inches wide
315 times 75%= 236.25 mm divided by 25.4 = 9.3 inches of sidewall
Height will = sidewall on top + Rim+ sidewall on bottom. 9.3+16+9.3 = 34.6 in

Make sense??

 

Completely, Thanks.

 

http://www.miata.net/garage/tirecalc.html