An RC gear ratio calculator helps you determine the final drive ratio, estimated top speed, and rollout distance for your RC car, truck, or crawler. By adjusting pinion and spur gear tooth counts, you can tune the balance between top speed and torque to match your motor, battery, and driving style.
Gearing Setup
Check your vehicle's manual. Use 1 if not applicable.
Results
| Pinion | Final Ratio | Top Speed |
|---|
How to Use the RC Gear Ratio Calculator
Getting the gearing right on your RC car makes the difference between a motor that overheats in three minutes and a build that runs cool all day while delivering the performance you want. This RC gear ratio calculator handles all the math so you can focus on tuning.
Step 1: Enter Your Gear Teeth Counts
Count the teeth on your pinion gear (the small one on the motor shaft) and your spur gear (the large plastic or composite gear it meshes with). These numbers are also usually printed on the gears themselves. The basic ratio is spur teeth ÷ pinion teeth — a 20-tooth pinion with an 82-tooth spur gives a 4.1:1 primary reduction.
Step 2: Add Motor KV and Battery Voltage
Motor KV is the RPM-per-volt rating printed on your motor. Multiply by battery voltage to get maximum no-load motor RPM. A 3200KV motor on 3S (11.1V) spins at approximately 35,520 RPM. Actual loaded RPM under driving conditions is typically 70–85% of this figure.
Step 3: Enter Tire Diameter
Measure your tire's outer diameter in millimeters or inches. This is the actual rolling diameter including any tread height. Tire diameter is critical for top speed calculations because a larger tire travels further per wheel revolution. You can switch between metric and imperial with the unit toggle at the top.
Reading the Results
The RC gear ratio calculator outputs your final drive ratio (primary × internal), estimated top speed, motor RPM, wheel RPM, and rollout distance. The comparison table shows speed and ratio for pinion sizes ±3 teeth from your current setup, making it easy to see how a one-tooth pinion change affects performance. Higher pinion = taller gearing = more speed but more heat. Lower pinion = shorter gearing = more torque and cooler motor.
Gearing for Your Use Case
For bashing, aim for a ratio that keeps motor temperature under 160°F (70°C) after a full battery run. For racing on smooth surfaces, run the tallest gear you can without heat-soaking the motor. For crawling and rock racing, go as short (numerically high ratio) as your gearbox allows — speed is irrelevant and low RPM keeps motor temps cool. Check the recommendation box for a custom tip based on your selected use case.
FAQ
Is this RC gear ratio calculator free?
Yes, this RC gear ratio calculator is completely free. No account or signup is required. Enter your pinion, spur, and motor specs to get instant results.
Is my data private when using this tool?
All calculations run entirely in your browser. No data is sent to any server or stored anywhere. Your RC build specs remain completely private.
What is the difference between pinion and spur gear in RC cars?
The pinion gear is the small gear attached to the motor shaft. The spur gear is the larger gear it meshes with. The ratio of spur teeth to pinion teeth gives the primary gear reduction. More pinion teeth (larger pinion) = higher speed, less torque. Fewer pinion teeth = more torque, less speed, cooler-running motors.
How do I calculate RC car top speed?
Top speed = (Motor KV × Battery Voltage × Tire Circumference) / (Final Drive Ratio × Efficiency Factor × 1000). The final drive ratio is the product of the pinion/spur ratio and the internal gearbox ratio. This calculator does all the math — just enter your pinion teeth, spur teeth, motor KV, voltage, and tire size.
What is the internal gear ratio in RC cars?
Many RC vehicles have an internal transmission or differential gear ratio built into the gearbox, separate from the pinion-spur reduction. RTR (ready-to-run) vehicles often have internal ratios between 2:1 and 4:1. The final drive ratio is the pinion-spur ratio multiplied by this internal ratio. Check your vehicle's manual for the internal ratio.
What is rollout distance in RC?
Rollout is the distance your RC car travels per revolution of the motor shaft, accounting for the full drive train. It tells you how 'tall' your gearing is. Higher rollout (more distance per motor rev) means top-speed biased gearing. Lower rollout means torque-biased gearing better for crawling, rough terrain, or acceleration.
What gear ratio is best for bashing vs racing vs crawling?
For bashing (speed + durability), use a moderate ratio that keeps motor temps under 160°F. For racing on smooth tracks, run the tallest ratio that still produces smooth acceleration without motor heat. For crawling and rock racing, use the lowest (most torque) ratio available — speed is irrelevant and motor temps won't be an issue since you're moving slowly.
How do I prevent my RC motor from overheating?
If the motor runs hot (over 160°F / 70°C after a 5-minute run), switch to a smaller pinion gear to reduce the gear ratio. This reduces motor load and temperature. Also check mesh spacing — too tight or too loose adds friction. Adding a motor heatsink and fan also helps for high-performance builds.