Torque arm installation.

[Arvind]

Hello.
I have 250 w ( 250 w continuous and 540 w peak ) front hub motor conversion kit installed on Giant Roam 3 Disc 2018 model. My bike has alloy or aluminium ( not sure ) suspension fork. But the fork is not made up of steel for sure. So for safety purpose I want to install torque arm on each side of the fork from Grin named TorqueArmV3.
But there is not enough spacing on the axle of the motor. How to solve this issue?
Is torque arm really necessary for such a setup?
Thanks.

 

[Admin]

Great question Arvind! That's a tricky situation, I've struggled trying to install torque arms in the past due to space limitations, wires, and axle length... just like you're showing here. Given the relative low power of your hub motor setup, it may be fine to skip the torque arm... but for legal reasons, I can't advise it! Here's a similar powered kit I reviewed that didn't come with a torque arm, that I happened to install on a cheap aluminum alloy suspension fork. It all seems very similar to your situation. I think the biggest risk is that over time the rocking motion of your keyed axle could start to chew into the aluminum alloy dropouts and eventually, the motor could push so hard that it spins the axle, twists your power cable (possibly ripping it), and wrecks both the fork and the motor. I haven't ever had a wheel completely fall off of a bike I was riding because the force of my body weight on the bike pushes down onto the axle... but I have spun wheels and wrecked motors before. I hope this feedback helps you make a good decision! I would suggest making sure the axle is screwed on tight and that you check it occasionally... easing into the power (using the throttle slowly or starting in low levels of assist) will also help

 

[tomjasz]

250W would be fine with a steel fork. I'm surprised to see a motor with that short of an axel. Perhaps thinner spacers/washers between the motor and fork? That will gain some.

On second look that appears to be a very thick dropout. I assume you've taken a magnet to the dropouts and determined as you wrote not steel?

 

[Arvind]

Great question Arvind! That's a tricky situation, I've struggled trying to install torque arms in the past due to space limitations, wires, and axle length... just like you're showing here. Given the relative low power of your hub motor setup, it may be fine to skip the torque arm... but for legal reasons, I can't advise it! Here's a similar powered kit I reviewed that didn't come with a torque arm, that I happened to install on a cheap aluminum alloy suspension fork. It all seems very similar to your situation. I think the biggest risk is that over time the rocking motion of your keyed axle could start to chew into the aluminum alloy dropouts and eventually, the motor could push so hard that it spins the axle, twists your power cable (possibly ripping it), and wrecks both the fork and the motor. I haven't ever had a wheel completely fall off of a bike I was riding because the force of my body weight on the bike pushes down onto the axle... but I have spun wheels and wrecked motors before. I hope this feedback helps you make a good decision! I would suggest making sure the axle is screwed on tight and that you check it occasionally... easing into the power (using the throttle slowly or starting in low levels of assist) will also help

Thanks Court for prompt and detailed reply.

 

[Arvind]

250W would be fine with a steel fork. I'm surprised to see a motor with that short of an axel. Perhaps thinner spacers/washers between the motor and fork? That will gain some.

On second look that appears to be a very thick dropout. I assume you've taken a magnet to the dropouts and determined as you wrote not steel?
[/QU

Thanks Thomas.
Yes I have tested dropouts with magnet and confirmed that they are not steel.

 

[tomjasz]

I'd sure want at least one torque arm. I'd use a thinner spacer between the inside fork and the motor, and if you have a source like McMaster Carr, or Fastenal, a thinner axle nut. I think you could gain the width of a Grin Torque arm. There are some TA's that are quite thin. I think you could adapt this one.

Torque Arm Amped Bike Style

Distributors and builders of life changing high power electric bikes.

lunacycle.com

 

[Arvind]

I'd sure want at least one torque arm. I'd use a thinner spacer between the inside fork and the motor, and if you have a source like McMaster Carr, or Fastenal, a thinner axle nut. I think you could gain the width of a Grin Torque arm. There are some TA's that are quite thin. I think you could adapt this one.

Torque Arm Amped Bike Style

Distributors and builders of life changing high power electric bikes.

lunacycle.com

Thank you Thomas for such a valuable information.

 

[tomjasz]

Thank you Thomas for such a valuable information.

You're welcome. It could go on the inside as well.