Arrma Infraction Gearing Guide — FDR, Pinion & Spur Chart

Arrma Infraction RC Gearing & Optimization Guide

Optimizing your gear ratio is one of the most effective ways to balance speed, torque, and electronics longevity in your Arrma Infraction 6S / 4X4 3S BLX (Speed-Run Street Car). 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 1/7 & 1/8 on-road speed-run street car platform with a 2.6 internal transmission ratio, even a single-tooth pinion change shifts your final drive ratio by 3-5%.

The Arrma Infraction is a purpose-built on-road speed-run and street basher. Because it runs low-profile slick tires and rides on a rigid on-road chassis, gearing is optimized for sustained high-RPM top speed rather than punch off the line. Stock Infraction 6S trucks trap in the mid-70 mph range; geared setups on 8S regularly break 100 mph on smooth pavement.

Speed-Run Aerodynamic & Tire Notes for the Arrma Infraction

At the extreme top-end speeds a Arrma Infraction is capable of, foam and rubber tires begin to balloon under centrifugal load, growing the effective rolling radius by 10-20% and quietly re-gearing the truck taller than any pinion change on the bench. That ballooning heavily strains the motor because your true FDR drops the moment the tires expand, so tracking motor RPM spikes with a data-logging ESC is far more reliable than trusting a static rollout number. Aerodynamic lift also becomes a real factor over long straightaways — the front end goes light, traction drops, and the motor sees less load spikes but higher sustained RPM, which is what actually kills rotors on speed-run passes.

🛠️ Essential Tools Required for Gearing Changes

Hex drivers (1.5mm, 2.0mm, or 2.5mm depending on the Arrma Infraction 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 Arrma Infraction, this trade-off is amplified by the fixed 2.6 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 46T 48-pitch spur. FDR is calculated as (spur ÷ pinion) × 2.6 internal ratio.

Pinion	Spur	FDR	Typical Use
14T	46T	8.54	Balanced club racing
16T	46T	7.48	Open outdoor / high-speed
18T	46T	6.64	Wide-open straights / mod motors
20T	46T	5.98	Wide-open straights / mod motors
22T	46T	5.44	Wide-open straights / mod motors

Understanding Pinion & Spur Gears

Stock 6S Infraction pinion is 16T mod-1 on a 46T spur. Speed-run tuners running 8S upgrade to 18T-20T pinions but must simultaneously upgrade to a 1900Kv or lower motor to keep ESC current draw safe.

Rollout Targets

Speed-run rollout numbers are meaningful only with a healthy dose of skepticism — Infraction tires balloon by more than 15% at top speed, which effectively re-gears the car taller than any bench measurement suggests.

Motor Temperature Management

Sustained top-speed passes are much harder on motor magnets than short bashing bursts. Data-log motor RPM with a compatible ESC and stop the run the instant the motor exceeds 190F (88C) — rotor demagnetization on speed-run passes is permanent.

⚠️ 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 Arrma Infraction 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 Arrma Infraction

The link below opens the calculator with Custom / Other Chassis pre-selected, the Arrma Infraction's internal ratio of 2.6 and its recommended battery of 6S LiPo (22.2V) 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 2.6 ratio + 6S LiPo (22.2V) preset →

Arrma Infraction 6S / 4X4 3S BLX (Speed-Run Street Car) Gearing Guide