Useful Tools
This calculator gives you a graphic display of the miles per hour your vehicle will be at when your present transmission shifts to the next higher gear. It then compares the results to the three popular GM overdrives. The engine rpm limit where these shifts will occur must be set by you.

In the top box, choose your present transmission from the drop down menu, enter either the P-metric size or actual measured size of your tire, enter your rear end ratio in decimal format (ie: 3.73), set the rpm limit and click "Calculate"

Your current transmission Wide Open RPM Limitation
P-Metric (not required if you only know the overall diameter)
Section Width Aspect Ratio Rim Size
Overall diameter (not required if you only know the P-Metric measurements)
inches
Rear end ratio (in decimal format. EX: 3.73, 4.10, 3.42)