Gearing is one of the simplest and most effective ways to change how your RC car performs. A single tooth change on the pinion gear can mean the difference between a car that accelerates hard out of corners and one that has a higher top speed on the straight. This guide explains how it all works.

What Is Gear Ratio?

Gear ratio is the relationship between two meshing gears. It tells you how many times the driving gear (the one attached to the motor) must turn to rotate the driven gear (the one attached to the drivetrain) once.

In an RC car, the two main gears you can change are:

• Pinion gear: The small gear on the motor shaft.
• Spur gear: The large gear on the transmission input.

The gear ratio is calculated by dividing the spur gear teeth by the pinion gear teeth. An 87T spur with a 22T pinion gives a ratio of 87 ÷ 22 = 3.95:1. This means the motor turns 3.95 times for every one turn of the spur gear.

Pinion and Spur Gears

Pinion Gear

The pinion is the small metal gear pressed onto the motor shaft. It is the primary gear you swap to adjust gearing. Pinion gears are sold in single-tooth increments (e.g., 18T, 19T, 20T). Changing the pinion by just one tooth has a noticeable effect on performance.

• Larger pinion = lower ratio = more top speed, less torque, hotter motor/ESC
• Smaller pinion = higher ratio = more torque, less top speed, cooler motor/ESC

Spur Gear

The spur gear is the large plastic or composite gear inside the transmission. It meshes with the pinion. Spur gears are available in different tooth counts, but they are swapped less frequently than pinions because the range is usually limited to 2-3 options per vehicle.

• Smaller spur = lower ratio = more top speed (same effect as a larger pinion)
• Larger spur = higher ratio = more torque (same effect as a smaller pinion)

Final Drive Ratio (FDR)

The final drive ratio accounts for all gearing between the motor and the wheels, including the internal transmission gears (which you typically cannot change). The formula is:

The internal ratio is fixed by your vehicle's transmission design. You can find it in the vehicle manual or spec sheet. For example:

FDR is the number that matters most when comparing setups across different vehicles, because it accounts for the full drivetrain.

Gearing for Speed vs Torque

For racing, gearing is usually track-specific. Tight, technical tracks reward shorter gearing (more accel). Long straights reward taller gearing (more speed). Use our Gear Ratio Calculator to experiment with different pinion/spur combos before buying.

How to Calculate Your Gear Ratio

1. Count pinion teeth. The tooth count is usually printed or engraved on the gear. If not, count them manually.
2. Count spur gear teeth. Same method. Common counts: 48P spurs range from 72T-90T; 32P spurs range from 50T-60T.
3. Divide spur by pinion. Example: 87T spur ÷ 22T pinion = 3.95 gear ratio.
4. Multiply by internal ratio. Find this in your vehicle manual. Example: 3.95 × 2.72 = 10.74 FDR.

When to Change Your Gearing

• Motor or ESC running hot: Gear down one tooth on the pinion. This is the most common reason to change gearing.
• Car feels sluggish off the line: Gear down for more torque.
• You want more top speed and temps are fine: Gear up one tooth at a time. Check motor temp after each change.
• Switching battery voltage: Going from 2S to 3S means more RPM. Gear down to compensate and keep temps safe.
• New track or surface: Loose dirt or carpet may need different gearing than smooth asphalt.

Common Gearing Mistakes

• Gearing too tall from the start: Running the biggest pinion you have to chase top speed. This overheats the motor and ESC. Always start conservative and gear up gradually.
• Ignoring gear mesh: After swapping a pinion, always check mesh. Too tight causes excessive friction and wear. Too loose causes gear skipping. A thin piece of paper between the gears during tightening gives a good starting mesh.
• Mixing gear pitch: 48-pitch and 32-pitch gears are not interchangeable. Make sure the pinion and spur are the same pitch (also called module in metric).
• Not checking temperature: After any gearing change, check motor temp with an IR thermometer after a 5-minute run. Stay under 170°F (77°C) for most setups.

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