Torque Arms for Hub Motor eBikes

oldguy

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Torque arms are used on ebikes with hub motors since the hub motor puts a lot of twisting torque on the drop outs - more torque that the bike was designed for. When running a front hub motor, torque arms are vital to prevent the front forks from snapping and the motor from spinning in the forks. There have been ebike riders who have died from not installing torque arms, so please be careful.


Aluminum Front Folks & Front Hub Motors

The more power the hub motor has, the more danger. If you have a 350Watts front hub motor than you will not have any problems. However, a more powerful front hub motor over 500 Watts or one that has been over amped will cause problems. To be on the safe side with aluminum folks and more powerful motors, at least 2 torque arms should be used - one on each side of the front forks.

This is what we are trying to avoid from happening:
ebike broken front fork.jpg


Electric bike home builders must be careful that they don't end up with broken front folks like in the picture above. Aluminum front forks are just NOT suitable for front mounted hub motors without modification. To make a front hub motor suitable for aluminum forks takes an expert electric bike builder who knows what he is doing. It requires steel reinforcement using torque arms.

For the first time ebike builder doing there first installation, we recommend you DO NOT install a front wheel hub motor kit UNLESS your forks are made from STEEL. You can test this by taking a magnet and putting it on the forks and see if it sticks. If it sticks it is STEEL - a much safer option for a front hub kit than aluminum.


Steel Bends, Aluminum Snaps

You have to understand that when aluminum is under a force it tends to snap without warning. Steel fails by bending rather than snapping and does not fatigue over time as quickly as aluminum.

Cheaper ebikes come with steel front forks as standard. Some aluminum bikes use steel front forks for extra strength. Alumimum is generally used for it's weight advantage - it is much lighter than steel.


Aluminum Frames & Rear Hub Motors

When using an aluminum frame on and ebike with powerful rear hub motor, a rear torque arm is recommended to be on the safe side. A rear failure will usually only result in a wheel lock up and a skid to a halt (rather than a possibly fatal face plant with a front hub motor) so it is not as serious an issue. Any decent enough aluminum frame should have strong enough rear dropouts.


Torque Arms

Torque arms come in many different shapes and styles and almost everybody sells them - here is one available on Amazon:
universal front fork torque arm.jpg
 
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