Gear Ratio Calculator
Calculate your final drive ratio from spur, pinion, and internal drive ratio.
8.16:1 final drive ratio
MOD 1 pitch
High FDR — more torque and acceleration, lower top speed. Good for technical terrain.
Matching spur gears for this tooth count
How to find your internal drive ratio
The internal drive ratio (IDR) is found in your vehicle's manual under drivetrain specs. Common examples: Traxxas Slash 4X4 ≈ 2.72, ARRMA Kraton 6S ≈ 2.6, Losi Super Baja Rey ≈ 2.25. If you can't find it, search "[your model] internal drive ratio" on the manufacturer's support page.
What does final drive ratio mean?
FDR tells you how many motor rotations produce one wheel rotation. Higher FDR = more torque multiplication, lower top speed. Lower FDR = more top speed, less torque.