Ok... I have a tuner, and I just got some new tires on my truck, What's the formula to use to determine the tire size?

Short of taking a measuring tape out to it and doing it this way

What's a more mathematic/Scientific way to determine the size? Shouldnt have skipped Math class so often!

265/70/17's

Much appreciated!

 

I think this is right--

265 is section width in mm (25.4 mm = 1 inch) 265/25.4 = 10.4 inches wide.

70 = series. This means the sidewall is 70% as tall as the section width so 10.4 X 70% = 7.3 inches tall

17 = diameter of the wheel in inches

 

There are lots of tire calculators out there--

http://www.discounttire.com/dtcs/infoTireMath.dos#row1

 

I have a Superchips tuner also and it's not as simple as punching in the exact size. When I had 285/75-16's, which are right at 33 inches tall, I punched in 33. Well, my speedo read 4 mph slow. I think I wound up putting in 32.25 to get a correct mph reading. I went through the same trial and error method when I moved up to 35's. I'm just glad I have access to a hand held radar so I didn't have to get someone to clock me.