Here is how I have been calculatingmy tires sizes with this formula:

Width x Aspect Ratio = Section Height (Section Height is the side wall, from rim edge to tread height)
Section Height x 2(The tire is made up of two sidewalls) = Combined Section Height
Combined Section Height + Wheel Diameter = Tire Diameter

Example 285/75R16 :
285mm X .75 = 213.75mm
213.75mm X 2 = 427.5
427.5mm + 406.4mm(16" rim) = 833.9 which is 32.83"
The side wall section height 213.75mm is 8.4154"

Example 255/85R16 :
255mm X .85 = 216.75mm
216.75mm X 2 = 433.5mm
433.5mm + 406.4 = 839.9mm which is 33.06"
The side wall section height216.75mm is 8.5335"

Example 315/75R16
315mm X .75 = 236.25mm
236.25 X 2 = 472.5mm
427.5mm + 406.4mm = 878.9mm which is 34.602"

BamAram, do you have any pictures of your truck that you could either post or send ? Do you have any issues withtire ballance, and what tires and rims are you using? I plan to keep the chrome ram rims.

 

i'm curious of the 315's i have a 3" lift up front and a 2" in the rear so is there gonna be a hella lot of rubbing or what? on anything?

 

i have the top gun coil lift. just finished the rear last weekend. i have kumho 265/75 16 for now. so far so good.