Overview
Replace your Arrma Grom's fragile factory rear bevel diff gears with the Hot Racing 30T/12T Steel Helical Diff Ring/Pinion Rear Gear Set — a high-torque, precision-machined drivetrain upgrade engineered specifically for the 1/18 4WD Grom platform. The CNC-cut helical spiral gear profile rolls into mesh smoothly under load, transferring more power with less noise than the original bevel-cut gears.
For Grom drivers running upgraded motors or tackling harsh terrain, this rear gear set is one of the most impactful drivetrain upgrades available. Stronger, smoother, and more efficient than stock — and precisely matched as a ring/pinion pair so engagement geometry is correct from the first install.
Key Features
- High-carbon steel CNC spiral-cut construction
- 30T helical ring gear + 12T helical pinion gear
- Significantly stronger than stock bevel gears
- Smoother, quieter operation under load
- Precision-matched as a ring/pinion set
Performance Benefits
- More efficient power transfer through the rear differential
- Higher torque capacity for upgraded motors and harsh terrain
- Reduced gear noise during operation
- Long-lasting durability — outlasts stock plastic-bevel setups
Usage Notes
Must be installed and replaced as a matched set — never mix this helical pinion with a stock bevel ring (or vice versa). Follow the kit manual for proper diff installation. Apply medium thread-locker (blue) on screws threading into metal. Hot Racing SPL10G05 high-temperature grease is recommended for the diff gears.
Technical Specs
- Material: High-carbon steel, CNC spiral-cut
- Tooth Counts: 30T ring / 12T pinion
- Gear Style: Helical spiral cut
- Position: Rear differential
- Replaces: Rear diff ring/pinion from Arrma ARA311177 and ARA31182
What's Included
- One (1) 30-tooth helical spiral-cut diff ring gear
- One (1) 12-tooth helical spiral-cut pinion gear
Fitment
- Arrma Grom 1/18 4WD (all variants)
- Replaces ARA311177 and ARA31182 rear diff ring/pinion
Summary
The Hot Racing 30T/12T Steel Helical Diff Ring/Pinion Rear Gear Set is the smartest drivetrain upgrade you can install on your Arrma Grom 4WD. Stronger gears, smoother operation, and more efficient power transfer — all in a precision-matched set that will last for the life of the vehicle.
