The spur gear is the cheapest part in your drivetrain and the one most likely to leave you pushing a truck back to the car. The usual story: it made a weird grinding "brrrap," then the motor screamed and the truck went nowhere. Pull the gear cover and half the teeth are gone, spread through the chassis like plastic glitter.
Traxxas says it plainly in its manuals: incorrect gear mesh is the most common cause of stripped spur gears. The fix doesn't cost anything. It takes a strip of paper, a hex driver and five minutes. Then there's gearing, the pinion and spur sizes that decide whether your truck is a rocket or a toaster. Get both right and spurs last. Get them wrong and you'll be on a first-name basis with our parts wall.
The Short Answer
Gear mesh should have a tiny bit of play (backlash) between the pinion and spur: tight enough that the teeth fully engage, loose enough that a strip of notebook paper rolls through the gears without binding.
- How to set it: loosen the motor screws, run a strip of paper between the gears, push the pinion into the spur, tighten, then remove the paper.
- Bigger pinion or smaller spur: more top speed, more heat and current draw. Smaller pinion or bigger spur: more punch, cooler running.
- Temperature check: Traxxas calls a motor too hot to touch (about 200°F) or a battery around 150°F a sign of over-gearing. Castle says to keep its motors under 180°F.
- Re-check mesh every time you change a gear, re-mount the motor, or hear a new noise.
1. How to Set Gear Mesh (and How Tight It Should Be)
"Mesh" is how deeply the pinion's teeth sit in the spur's teeth. Too tight and the gears bind, heat up and eat motor bearings. Too loose and the teeth ride on their tips until they shear off. That's the classic stripped spur.
The paper method, step by step
This is the method Traxxas prints in the Slash manual and its other owner's manuals. It works on most 1/10 trucks.
- Unplug the battery and remove the gear cover.
- Loosen the motor mounting screws just enough that the motor slides.
- Cut a narrow strip of ordinary notebook paper and feed it into the mesh between the pinion and spur.
- Push the motor so the pinion presses into the spur with the paper trapped between them.
- Tighten the motor screws, then roll the paper out by turning the spur.
- Run a fresh strip through. It should pass without binding the gears.
Then do the feel test: hold the spur still and rock the pinion. You want a tiny click of free play. Zero play is too tight. A visible wobble is too loose.
Check it all the way around
Spurs aren't perfectly round, and a slightly bent motor shaft makes a pinion wobble. Rotate the spur a quarter turn at a time and check play at each point. Set the mesh at the tightest spot. If one spot binds and another rattles, replace the warped spur or check the motor shaft.
Lock it down
Two screws cause more stripped spurs than bad drivers:
- Motor mount screws: if they back out, the motor slides away from the spur and mesh loosens on its own. Use the correct length (Traxxas warns that motor screws that are too long can damage the motor) and a dab of blue threadlock on metal-to-metal threads.
- Pinion set screw: tighten it on the flat of the motor shaft, with threadlock. A slipping pinion sounds like a stripped spur and chews it up fast.
Some newer trucks, like the Traxxas XRT and Maxx, use a locating pin system that sets mesh for each gearing option. Use the paper method when you're between pin positions or running gears the chart doesn't list.
2. Pinion vs. Spur: What Changes Speed, Punch and Heat
Your motor spins fast. Gearing trades that speed for torque. Two numbers control it: pinion teeth (on the motor) and spur teeth (on the transmission).
The rules of thumb
- Bigger pinion = higher gearing: more top speed, slower acceleration, more current draw, more heat.
- Smaller pinion = lower gearing: more punch, less top speed, cooler motor and ESC.
- The spur works the opposite way: a bigger spur lowers gearing, a smaller spur raises it.
- One tooth on the pinion makes a bigger difference than one tooth on the spur.
Traxxas' manuals put it in two lines: use a lower gear ratio (numerically larger) to reduce current draw and temperatures, and a higher ratio (numerically lower) for top speed. High-speed gearing is for hard surfaces, not off-road or repeated stop-and-go.
A real example: Slash 2WD
| Pinion / spur (Slash 2WD, 48P) | Final drive ratio | Traxxas' use case |
|---|---|---|
| 14T / 90T | 17.49:1 | Fast acceleration, small tracks, short distances (optional pinion) |
| 16T / 90T | 15.30:1 | Good acceleration and speed, normal conditions |
| 23T / 86T | 10.17:1 | High top speed on hard surfaces only |
Ratios from the gearing chart in the Slash 2WD owner's manual (spur ÷ pinion × 2.72 internal ratio). A higher number means lower gearing: more punch, less top speed, cooler temperatures.
We stock all three combos: the Traxxas Pinion Gear 14T 48P (2427), Traxxas Pinion Gear 16T 48P (2416) and Traxxas Pinion Gear 23T 48P (2423) pinions plus the Traxxas Spur Gear 90T 48P (4690) and Traxxas Spur Gear 86T 48P (4686) spurs. For bashing in Georgia red clay and tall grass, the 14T or 16T on a 90T spur keeps a truck happy. Save the 23T for the parking lot.
Match the pitch, always
Pitch is tooth size. A 48-pitch (48P) pinion only meshes with a 48P spur. Many 3S and 4S bashers use 32P or 0.8 Mod gears, which Traxxas labels as compatible with each other. Never mix 48P with 32P or 0.8 Mod: they'll "fit" for about one battery. ARRMA's 3S and 4S BLX 4x4 trucks use a 57T 0.8 Mod spur, and the ARRMA HD Steel 57T Spur Gear, 0.8 Mod (ARA310945) is the steel upgrade for owners who keep stripping the stock one. Check your manual for your exact model's part number.
3. Why Spurs Strip (Besides Mesh) and How to Gear by Temperature
If you've set the mesh right and still strip spurs, something else is loading those teeth.
The usual suspects
- Slipper clutch too tight: on trucks with a slipper, it's the shock absorber for the spur. Traxxas' Slash manual says to set it so it slips about two feet from a full-throttle standing start on carpet, and never to run it fully compressed.
- Landing on the throttle: a wide-open wheel landing a jump slams the drivetrain. Let off before the wheels touch down.
- Debris: a pebble in an open gear cover strips teeth instantly. Keep covers on and check after every dirt run.
- Flexing motor mount: loose or cracked mounts let mesh open up under load.
- Too much power for plastic: on 3S and up, a steel spur may be worth it. See our ARRMA 223S breakage guide.
Gearing by temperature
Gear changes are a heat experiment. Run five minutes, stop, and check the motor, ESC and battery. Traxxas' rule: if the battery is extremely hot (about 150°F) or the motor is too hot to touch (about 200°F), you're probably over-geared. Castle Creations goes further for its motors: "Never let the motor get above 180°F," and check temps frequently on the first run after any gearing change (Castle motor user guide). An inexpensive infrared temp gun takes the guesswork out.
Don't gear by temperature after wet runs. Traxxas notes that water cools the motor and gives a false reading.
A quick gearing-change procedure
- Start with the smallest pinion and largest spur listed for your model (Castle's advice too).
- Change one tooth at a time on the pinion.
- Re-set mesh with the paper method every time.
- Run five minutes and check temps.
- If it's cool, go up a tooth. If it's hot, go back down. If the ESC is in thermal shutdown (fast red blinks on a Traxxas), gear down. Our Traxxas blinking-light guide decodes those.
ARRMA has a short video on meshing gears like a pro if you want to see the feel test in action.
Conclusion
Stripped spurs aren't bad luck. They're a mesh that was too loose, a motor screw that backed out, a slipper cranked down or gearing that's too tall for the terrain. Set mesh with the paper method, lock the screws with threadlock, gear for your surface and check temperatures after every change. A $10 spur should last months, not minutes.
Shop replacement drivetrain parts, including pinions, spurs and steel upgrades. Or bring your truck by the store and we'll set the mesh while you watch, no charge for the lesson.
Gear Mentioned in This Guide
ARRMA HD Steel 57T Spur Gear, 0.8 Mod (ARA310945)
Steel spur for ARRMA 3S and 4S BLX 4x4 trucks.
Shop now
Frequently Asked Questions
How tight should gear mesh be?
Tight enough that the teeth fully engage, with a tiny bit of free play. A strip of notebook paper should roll through the gears without binding. Hold the spur and rock the pinion: you should feel a slight click, not zero movement and not a wobble.
Pinion vs. spur: what changes speed and heat?
A bigger pinion or smaller spur raises gearing: more top speed, more current and heat. A smaller pinion or bigger spur lowers gearing: more acceleration, cooler running. Pinion changes have a bigger effect per tooth.
Why does my RC keep stripping spur gears?
The most common cause is incorrect gear mesh. Other causes are loose motor screws, a slipped pinion set screw, an over-tightened slipper clutch, debris in the gears, landing jumps on throttle and too much power for a plastic spur.
How hot is too hot for an RC motor?
Traxxas says a motor too hot to touch (about 200°F) or a battery around 150°F means you're probably over-geared. Castle Creations says to never let its motors exceed 180°F. Check with an IR temp gun after five minutes.
Do I need to reset gear mesh after changing the pinion?
Yes. Any time you change a pinion or spur, or remove and reinstall the motor, re-set the mesh. Traxxas says to check and adjust gear mesh whenever a gear is replaced.
Can I use a 32P pinion with a 48P spur?
No. Pitches must match. 48P meshes only with 48P. 32P and 0.8 Mod are close enough that Traxxas sells 0.8 metric pitch spurs as 32P-compatible, but never mix either one with 48P.
Sources and Further Reading
- Traxxas: Slash 2WD XL-5 owner's manual (gear mesh, gearing chart, slipper clutch)
- Traxxas: Rustler 4X4 Ultimate owner's manual (gearing and temperatures)
- Traxxas: Maxx Ultimate owner's manual (pin mesh system)
- Castle Creations: Motor User Guide
- ARRMA: Tricks & Tips, mesh gears like a pro
- Traxxas: VXL Model Runs Momentarily and Slows Down/Stops
