How to Change a Pinion Gear on an RC Car

Why would you change a pinion gear?

Swapping the pinion is the fastest way to change how a car feels without touching anything else on the drivetrain. A smaller pinion lowers the overall gear ratio, trading top speed for more torque and quicker acceleration off the line. A larger pinion raises the ratio, giving more top speed at the cost of acceleration and, often, more motor heat.

It is also a common fix when a motor runs hot: see the RC motor temperature guide for when gearing down is the right call versus checking the drivetrain and battery first.

What pinion pitch do you need: 48P, 32P, Mod1 or 0.8 Mod?

Pitch (or module, for metric gears) describes the tooth size and spacing, and it has to match your spur gear exactly, not just be close. A 48 pitch pinion will not mesh correctly with a 32 pitch spur even if the tooth counts look similar on paper; the teeth are physically a different size and shape.

48 pitch is common on smaller, lighter 1/10 electric touring and short course setups. 32 pitch and metric Mod 1 gears show up more on 1/8 and heavier 1/10 trucks that need bigger, stronger teeth. 0.8 Mod is common on lighter buggies like the ARRMA Typhon GROM line. When in doubt, check what pitch is stamped on your current spur gear or listed in your car's manual before ordering a new pinion.

How do you match your new pinion to your spur gear?

Before you order a pinion, confirm your spur gear's pitch and current tooth count. A spur like a Steel Spur Gear Set 48P 86T at $16.39 tells you both numbers right in the listing: 48 pitch, 86 teeth. Match the pitch exactly, then choose a pinion tooth count based on whether you want more torque (fewer teeth) or more top speed (more teeth).

Buying a pinion in the wrong pitch is the single most common gearing mistake. It will often look close enough to slide onto the shaft, then strip both gears within the first pack.

How do you actually change the pinion, step by step?

• Disconnect the battery before touching the drivetrain.
• Loosen, but don't fully remove, the two motor mount screws so the motor can pivot slightly on the chassis.
• Loosen the pinion's set screw with a hex driver, then slide the old pinion off the motor shaft.
• Slide the new pinion onto the shaft, lining it up with the shaft's flat spot, and leave the set screw loose for now.
• Fold a single sheet of ordinary printer paper and slip it between the pinion and spur gear teeth.
• Pivot the motor toward the spur gear until the pinion just presses the paper against the spur, then tighten both motor mount screws while holding that position.
• Remove the paper, then tighten the pinion's set screw firmly onto the shaft's flat.
• Spin the wheels by hand: mesh should sound like a faint, smooth whisper, not a tight grinding rub and not a loose rattly slop.

Why does the paper method work for setting gear mesh?

Gear mesh needs a small, consistent running clearance between the pinion and spur teeth. Too tight, and the gears bind under load, which spikes motor current and heat within minutes. Too loose, and the teeth only make partial contact, which strips them under hard acceleration.

A single sheet of ordinary printer paper happens to be close to the running clearance most 48P and 32P gear manufacturers design around, which is why it has been the standard shop trick for decades. It is not a precision gauge, but it is repeatable, free, and close enough for real-world driving.

How do you know which tooth count to pick?

Once the pitch is settled, tooth count is the tuning knob. Fewer teeth on the pinion lowers your final drive ratio (more torque, less top speed, cooler running); more teeth raises it (more top speed, less torque, more heat). Run the numbers for your specific spur, internal ratio and tire size with the gear ratio and top speed calculator, or use the pinion and spur swap calculator to see the effect of a single tooth change before you buy anything.

For the underlying math, see how to calculate RC car gear ratio and RC car gearing explained.

What tools do you need to change a pinion gear?

Most pinion swaps only need two things: a small hex driver to loosen the motor mount screws and the pinion's set screw, and the new pinion itself. A compact kit like the 10 in 1 RC Model Repair Tools Kit at $16.98 covers the common hex sizes from 1.5mm up to 5.5mm, which handles both the motor mount and set screw on almost any 1/10 to 1/8 scale car.