Please Note: These part numbers are for the standard style pinion gear. The last two numbers of the part number is the number of teeth for the gear (Example 2538943 = 43 teeth).
Here is an example on how to calculate the wheel diameter to select a speedometer gear to use with the desired ring/pinion gear.
- Tire Size: 245/60/15
- 245mm/25.4mm = 9.64 Inches Section Width
- 9.64 in. X 60% = 5.79 in. Side Wall Thickness
- 5.79 in. X 2 = 11.57 in. Total Side wall height
- 11.57 in. + 15 in. (Rim Size) = 26.6 in. Diameter
So with this Tire Size and 3.91 Gears, I would use a 40 Tooth Speedometer gear.