Reverse solve gear ratios, final drive, tire size, or RPM

Identify unknown gearing values from observed speed and RPM data.

What do you want to solve for?

Select the unknown value — provide the rest

Use this when you know your speed and RPM but don't know your rear diff ratio

Known Values

Enter the values you know — the result updates live

Speed (MPH)

RPM

Gear Ratio

Tire Size

Width (mm)

Aspect Ratio

Wheel (in)

275/35R20

Result

Final Drive Ratio

4.102:1

Find the final drive (rear diff) ratio

Formula used

Final Drive = (RPM x 60) / (Speed x Gear Ratio x Revs Per Mile)

= (3000 x 60) / (60 x 1 x revs/mi)