Enter RC Gear Setup
Example Data Table
Use these sample values to compare common electric RC gearing choices.
| Setup | Pinion | Spur | Internal Ratio | KV | Voltage | Wheel Diameter | Use Case |
|---|---|---|---|---|---|---|---|
| Conservative buggy | 18 | 87 | 2.60 | 3500 | 7.4 | 65 mm | Cooler track runs |
| Balanced touring | 24 | 78 | 2.13 | 4000 | 7.4 | 63 mm | Mixed speed and punch |
| Speed setup | 28 | 76 | 2.00 | 4600 | 11.1 | 70 mm | Short high speed passes |
Formula Used
Gear Ratio: spur teeth ÷ pinion teeth
Final Drive Ratio: gear ratio × internal drive ratio
No Load RPM: motor KV × battery voltage
Loaded RPM: no load RPM × drivetrain efficiency
Wheel RPM: loaded RPM ÷ final drive ratio
Speed: wheel RPM × tire circumference × 60
Rollout: tire circumference ÷ final drive ratio
Torque Multiplier: final drive ratio × drivetrain efficiency
The load index is an estimate. It compares pinion size, spur size, voltage, motor KV, wheel size, and internal gearing. It is not a replacement for real motor temperature checks.
How to Use This Calculator
- Enter the pinion teeth fitted to the motor shaft.
- Enter the spur gear teeth fitted to the transmission.
- Add the internal drive ratio from your vehicle manual.
- Enter motor KV and battery voltage.
- Measure tire diameter under normal running condition.
- Add tire growth if tires expand at high speed.
- Set drivetrain efficiency. Use 80 to 90 percent for many RC cars.
- Press calculate and compare speed, rollout, torque, and heat risk.
RC Pinion Gear Tuning Guide
Why Pinion Size Matters
The pinion gear is small, but it changes the whole drive feel. A larger pinion raises speed. It also raises motor load. A smaller pinion lowers speed. It usually improves punch and heat control. This calculator helps you compare those changes before testing. It gives speed, rollout, final drive ratio, and risk clues.
Understanding Final Drive
Final drive ratio combines the spur, pinion, and internal gears. A higher final drive gives more torque multiplication. It helps acceleration and reduces motor strain. A lower final drive gives more wheel speed. It may suit long straights and speed passes. It can also overheat the motor if used too hard.
Rollout and Track Feel
Rollout shows how far the car moves per motor turn. More rollout often means higher top speed. Less rollout often means sharper throttle response. Tire diameter affects rollout strongly. Worn tires can reduce speed. Ballooning tires can raise speed, but control may suffer.
Heat and Efficiency
Motor heat is the best warning sign. Gear changes should be tested in short runs first. Check motor, speed control, and battery temperature. Stop early when parts become too hot to touch. Efficiency also matters. Bearings, mesh, tires, and driveline drag can reduce real speed. Use realistic efficiency values for better estimates.
Practical Setup Advice
Change gearing in small steps. Move one or two pinion teeth at a time. Record speed and temperature after each run. Compare lap time, not only top speed. The fastest gear is not always the best race gear. A balanced setup feels smooth, stays cool, and finishes strong.
Frequently Asked Questions
1. What does a larger pinion gear do?
A larger pinion usually increases top speed. It lowers the final drive ratio. This can add motor load and heat. Test larger pinions slowly and check temperatures after short runs.
2. What does a smaller pinion gear do?
A smaller pinion usually improves acceleration and reduces heat. It raises the final drive ratio. Top speed may drop, but the car can feel stronger out of corners.
3. What is final drive ratio?
Final drive ratio combines spur gear ratio with the internal transmission ratio. It shows the total gear reduction between the motor and wheels.
4. What is rollout in RC gearing?
Rollout is the distance the car travels for one motor revolution. It depends on tire circumference and final drive ratio. Higher rollout often means more speed.
5. Why is my real speed lower than calculated speed?
Real speed can be lower because of drag, tire slip, voltage sag, bearing friction, and motor load. The calculator uses efficiency to reduce ideal speed.
6. How hot is too hot for an RC motor?
Many users try to keep motors below about 80°C. Limits vary by motor design. Always follow the manufacturer guide and use a temperature tool.
7. Should I tune by speed or temperature?
Use both. Speed shows performance, while temperature shows safety. A setup that is fast but overheats is not reliable for long runs.
8. Can this calculator choose the perfect race gear?
It gives a strong estimate. Track grip, driving style, airflow, timing, and tires still matter. Use the result as a starting point for testing.