Traxxas TRX-4 Brushless Gearing Guide — FDR, Pinion & Spur Chart

Traxxas TRX-4 Brushless RC Gearing & Optimization Guide

Optimizing your gear ratio is one of the most effective ways to balance speed, torque, and electronics longevity in your Traxxas TRX-4 (Brushless Conversion). The relationship between your pinion gear (attached to the motor) and your spur gear (attached to the transmission) dictates how hard your motor has to work — and on a 1/10 rock crawler & scale trail truck platform with a 40.66 internal transmission ratio, even a single-tooth pinion change shifts your final drive ratio by 3-5%.

A brushless-converted TRX-4 replaces the Titan 21T with a low-Kv sensored crawler motor (1200-2100Kv) and a crawler-spec ESC with drag brake and low-voltage cutoff. The sensored setup restores fine throttle control that a sensorless brushless motor cannot deliver at crawling speed. Because the ESC now determines drag brake, punch curve, and LiPo cutoff, ESC programming is a bigger tuning lever than pinion size on this configuration.

Rock Crawler & Trail Truck Drivetrain Notes for the Traxxas TRX-4 Brushless

Ultra-low speed crawling on a Traxxas TRX-4 Brushless demands heavy grease packed into the portal or straight axles to damp shock loading and keep the ring-and-pinion quiet under sustained torque. Whether you are running a precisely tuned slipper clutch or a fully locked differential, the goal is to make the drivetrain deliver torque smoothly instead of shock-loading it into a rock face. High-torque binds against a ledge can spike amp draw well past continuous ratings and overheat the motor even at walking pace, so a small in-line wattmeter or an ESC with current logging is worth more than another temperature reading — heat shows up long after the damage is already done.

🛠️ Essential Tools Required for Gearing Changes

Hex drivers (1.5mm, 2.0mm, or 2.5mm depending on the Traxxas TRX-4 Brushless variant)
Paper strip (for setting precise gear mesh)
Infrared temperature gun (crucial for monitoring motor heat after each run)
Threadlock (for the pinion gear grub screw)
Pinion gear puller (recommended when swapping gears on a hot motor shaft)

📋 Comprehensive Gearing & Temperature Guide

1. Understanding Pinion vs. Spur Gear Adjustment

Changing your gears alters your final drive ratio. Installing a larger pinion gear or a smaller spur gear increases top-end speed but increases the load on the motor, causing it to run hotter. Conversely, a smaller pinion or larger spur increases torque and acceleration while lowering top speeds and keeping your motor cool. On the Traxxas TRX-4 Brushless, this trade-off is amplified by the fixed 40.66 internal ratio — small external changes have a direct thermal consequence.

2. How to Set a Perfect Gear Mesh

Improper gear mesh will quickly strip your spur gear or bind your drivetrain.

Loosen the motor mount screws slightly.
Place a small strip of standard notebook paper between the pinion and spur gear teeth.
Press the gears tightly together and tighten the motor mount screws.
Roll the paper out. The paper should have clean, crisp crinkles without ripping.

Recommended Pinion & Spur Chart

All combinations use a 45T 48-pitch spur. FDR is calculated as (spur ÷ pinion) × 40.66 internal ratio.

Pinion	Spur	FDR	Typical Use
11T	45T	166.34	High-bite carpet / tight indoor
13T	45T	140.75	High-bite carpet / tight indoor
15T	45T	121.98	High-bite carpet / tight indoor
17T	45T	107.63	High-bite carpet / tight indoor
19T	45T	96.3	High-bite carpet / tight indoor

Understanding Pinion & Spur Gears

Most brushless TRX-4 conversions keep the 16T pinion / 45T spur and let motor Kv choose the top-speed envelope. Anything above 2500Kv sacrifices the fine-throttle control that makes the platform special.

Rollout Targets

Rollout on a brushless-converted TRX-4 remains a fraction of an inch per motor revolution — the portal axle reduction dominates any pinion change.

Motor Temperature Management

Brushless crawler motors on the TRX-4 should stay under 160F (71C) even at extended stall. If the motor exceeds 170F, the ESC's drag brake percentage is likely too high — the motor is fighting itself at zero throttle. A capacitor pack on the ESC input smooths high-torque transients on 3S.

⚠️ Critical Safety & Temperature Warning

Always use an infrared thermometer to check your motor and ESC temperatures during a run. RC electric brushless motors should never exceed 160°F (71°C). Exceeding 180°F (82°C) risks permanently demagnetizing your motor rotor and frying your Electronic Speed Controller. If your Traxxas TRX-4 Brushless is running above these thresholds, you must "gear down" by installing a smaller pinion gear immediately, improve airflow with a larger motor fan, and inspect the drivetrain for binding.

Calculate a custom FDR for your Traxxas TRX-4 Brushless

The link below opens the calculator with Custom / Other Chassis pre-selected, the Traxxas TRX-4 Brushless's internal ratio of 40.66 and its recommended battery of 3S LiPo (11.1V) already set — just plug in your pinion, spur, motor, and tire to see top speed, runtime, and FDR for your exact setup.

Open calculator with 40.66 ratio + 3S LiPo (11.1V) preset →

⚡ Brushless, ESC Programming & LiPo Care for the Traxxas TRX-4 Brushless

Brushless setups on the Traxxas TRX-4 Brushless shift the tuning burden away from the motor itself (which has no brushes or comm to wear) and onto ESC programming and LiPo pack management. At 3S and above, the ESC settings you never touch are almost always the reason a brushless motor dies early.

1. ESC programming that actually matters

Timing — leave at low or factory for bashing. High-timing profiles gain top speed but add 15-25F to the motor at the same pinion. Racing only.
Punch / throttle profile — drop from linear to soft on high-Kv sensorless setups; the softer curve reduces peak current draw off the line and dramatically lowers ESC temperature over a pack.
Drag brake — set as low as the driving style allows. High drag brake on a crawler holds the motor actively at zero throttle, which is how sensored crawler motors overheat without ever moving.
LiPo cutoff — set to 3.2V or 3.3V per cell. This is the single most important pack-preservation setting and is why LiPo packs die from over-discharge.

2. Sensor cables and capacitors

Sensored setups on the Traxxas TRX-4 Brushless are only as reliable as the sensor cable — inspect for chafing at every re-body and replace at the first sign of insulation wear. On 4S and above, add a dedicated capacitor pack to the ESC power input; the extra bulk capacitance flattens voltage spikes on hard-throttle transients and is the difference between a five-year ESC and a warranty claim.

3. LiPo care and storage

Storage voltage — 3.80-3.85V per cell. Never leave a pack fully charged for more than 24 hours.
Balance charge every cycle. Cell drift is the leading cause of pack retirement, and a fast charger's balance step catches it before it becomes dangerous.
Retire the pack when it puffs visibly, when internal resistance climbs above 12-15 mΩ per cell, or when usable capacity drops below 80% of rated. Puffed packs are a fire risk — discharge and dispose properly, do not "just one more run" them.
Never charge a warm pack. Let it drop to ambient before plugging it into the charger.

Rule of thumb on the Traxxas TRX-4 Brushless: brushless motors do not "wear out" the way brushed motors do — they die from heat, from ESC settings, or from LiPo abuse. Fix those three and the motor outlasts the truck.

Traxxas TRX-4 (Brushless Conversion) Gearing Guide