Uploaded October 2019 | Updated September 2026, 2 weeks ago
***** Repost after original video upload accidentally got deleted from youtube*****
In this video we show the process of installing the GMAC motor on a typical mountain bike frame and we detail some of the intricacies of the torque arm positioning. The torque arm itself is made up of 3 pieces:
1) A round torque plate machined from 7075 aluminum that slides over the splined axle and has a cutout slot for the motor cable.
2) A curved arm piece that encircles the the torque plate and moves the torque further down the chainstay to reduce the forces present on the frame.
3) A frame holder that secures to the chainstay with two hose clamps and provides a secure attachment point for the end of the arm. (Please do NOT use a conventional 'P' clamp for this, they are prone to fatigue failing at the torque levels of this motor).
On the initial installation, it is important to choose a relative orientation between the torque plate and the torque arm such that the cable exits through the dropout slot so that it doesn't get crushed when the axle nuts are tightened. .
Once everything has been installed correctly, removing and re-mounting the motor on the bike after that (to fix a flat, swap tires, upgrade sprockets etc) is fast and easy. Only the one M5 bolt between the torque arm and frame holder needs to be loosened to free the motor from the frame.
You do not need to remove the torque arm itself form the wheel ever again except in the case of replacing the disk rotor. And given the amazing regen possible with the GMAC, it's unlikely you'll ever need to replacing your brake pads, let alone an actual disk rotor!
***** Repost after original video upload accidentally got deleted from youtube*****
In this video we show the process of installing the GMAC motor on a typical mountain bike frame and we detail some of the intricacies of the torque arm positioning. The torque arm itself is made up of 3 pieces:
1) A round torque plate machined from 7075 aluminum that slides over the splined axle and has a cutout slot for the motor cable.
2) A curved arm piece that encircles the the torque plate and moves the torque further down the chainstay to reduce the forces present on the frame.
3) A frame holder that secures to the chainstay with two hose clamps and provides a secure attachment point for the end of the arm. (Please do NOT use a conventional 'P' clamp for this, they are prone to fatigue failing at the torque levels of this motor).
On the initial installation, it is important to choose a relative orientation between the torque plate and the torque arm such that the cable exits through the dropout slot so that it doesn't get crushed when the axle nuts are tightened. .
Once everything has been installed correctly, removing and re-mounting the motor on the bike after that (to fix a flat, swap tires, upgrade sprockets etc) is fast and easy. Only the one M5 bolt between the torque arm and frame holder needs to be loosened to free the motor from the frame.
You do not need to remove the torque arm itself form the wheel ever again except in the case of replacing the disk rotor. And given the amazing regen possible with the GMAC, it's unlikely you'll ever need to replacing your brake pads, let alone an actual disk rotor!
