E-Bike Torque Arm Set for Rear Hub Motors
Description
Torque Arm Set for eBike Hub Motor – Steel, 135mm QR Axle, for 500W–3000W Conversion Kits
Set of 2 steel torque arms for rear hub motors with 135mm quick-release axle. Arm length 86mm, axle opening 10mm x 14mm, thickness 3–4mm. Prevents motor axle rotation in the frame dropouts under high torque — a mandatory safety component for any 500W and above conversion kit on aluminium frames, and for 1000W+ on any frame type.
Brushless hub motors generate significant torque forces during acceleration — at 1000W and 48V, motor torque can exceed 40–80 N.m applied directly to the axle. Without a torque arm, this force is carried entirely by the flat sides of the axle against the aluminium dropout. On aluminium frames or at higher power levels, the axle begins to rotate inside the dropout, progressively widening the slot until the frame is irreversibly damaged or wheel control is lost while riding.
Torque Arm Set Technical Specifications
Dimensions and Material
Compatibility
Set Contents
Why a torque arm is mandatory at 500W+ — not optional
At low power (250W, 36V), torsional force on the axle is 10–20 N.m — small enough for the standard flat axle sides to handle alone on steel frames with thick dropouts. At 500W and above, or on any aluminium frame, the equation changes:
- Aluminium frames at any power of 500W+ — aluminium is softer than the steel axle and wears quickly under repeated force
- Any frame at 1000W+ — torque exceeds the capacity of any standard dropout, regardless of material
- Systems with regenerative braking — force acts in both directions (acceleration and braking), doubling dropout wear
The thickness rule — why 5mm matters
A 3mm torque arm provides resistance of 20–30 N.m — sufficient for 500W. At 1000W and above, torque exceeds this limit and the arm can fail by cutting a slot around the axle, damaging both the arm and the dropout. For 1000W–3000W systems, we recommend using both torque arms from the set simultaneously (left + right) to double the contact area and distribute force across both sides of the axle.
The 4mm dropout rule
If the frame dropout thickness is under 4mm (common on modern aluminium MTB or road frames), mount the torque arm in "sandwich" style — one on the outside and a steel plate on the inside — to double the grip surface. Measure the dropout thickness with a calliper before ordering if unsure.
Which Kits It's Recommended For
500W–1000W on Aluminium Frame
Mandatory for any MTX 500W or 1000W conversion on an aluminium frame — prevents dropout wear from the first ride.
1500W–3000W on Any Frame
Mandatory for all MTX 1500W, 2000W and 3000W kits regardless of frame material — torque exceeds the capacity of any standard dropout.
Systems with Regenerative Braking
Essential for any system with active regenerative ABS — force acts in both directions and dropout wear is double compared to a system without regenerative braking.
Correct Installation
Installation Steps
- Loosen the motor axle nut and remove the wheel from the frame
- Slide the torque arm onto the axle with the 10x14mm opening on the flat sides of the axle
- Refit the wheel in the frame and tighten the axle nut
- Fix the torque arm to the frame using the included C-clamp or a frame eyelet
- Check that the arm is not parallel to the axle — it must form an angle for force distribution
- Repeat on both sides of the axle for 1000W+ systems
Post-Installation Checks
- Test under hard acceleration with the wheel lifted — the axle must not move
- Periodically check axle nut and torque arm bolt tightness
- Visually inspect the dropout after the first 100km of intensive use
- If the arm bends or the dropout shows wear marks, add the second torque arm