The sidewall number is a percentage of the width number, I don't know the math off the top. But Like my 275/40 17 has the same sidewall as a 255/50 16.
I'm asking if I should make the rear tire a little taller basically. Right now it's a 315/35, and I am contemplating going 315/40 if I can find the tires. I just haven't decided yet.
Looks like that's what it will be. A lady at work can get me 555's for 194 a piece, so before I quit I'm gonna snag 2 for when these tires decide they've had enough haha!