the "245" is the tread width in mm's. The "75" is the aspect ratio (the sidewall is 75% of the tread width.)

 

You can use this to figure out your tire diameter:
https://www.dieselbombers.com/calculators.php

After you have the diameter, use one of the following for circumference:

pi(3.14) x Diameter

OR

2 x pi(3.14) x Radius.

Enter the calculated number into the chip, should work out.

With your stock tires you have a diameter of 30.47".
30.47" x 3.14 = 95.6758"

If your new tires are 315/75R16's, they will have a diameter of 34.6".
34.6" x 3.14 = 108.644"

 

Does the Attitude read in tire diameter? I only ask because my Quad Pulse reads the tire size in the circumference of the tire.

 

My Attitude uses circumference. It is the older, pre-cs/cts monitor.

 

It's actually the cross section width (sidewall to sidewall at the widest point) the actual tread isn't as wide as the cross section

 

I put these numbers in this morning and it's working a lot better, so thanks, you're awesome

 

No problem at all! I fought with the same thing when I first got my truck. I'm more than happy to share the knowledge I have acquired.