Broken Forks

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youngsoulrebel
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Joined: 02/13/2010
Points: 19

I have an electric bicycle that is powered with a front wheel motor. I have been using the bike regularly for 3 years with no major issues.
Recently, the front forks of the bicycle (it's a giant mountain bike) sheared off (where the wheel connects to the forks). I had wondered if this might happen. A bicycle is designed to be powered via pedals not via the front wheel.
The forks were replaced but the same thing happened a week later.
Has anyone had any similar experiences or can recommend a 'strengthened' set of forks that may prevent this from happening again.

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pcarlson1979
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Joined: 02/20/2011
Points: 459
Re: Broken Forks

Hi there.

Yes I've had a lot of experience with front forks breaking from being powered by a front hub motor. The best thing I ever did was to buy a Cro-Molly STEEL front fork. If the front forks are not steel then they WILL fail, it's only a matter of time. If you're not sure, take a magnet and see if it sticks strongly to a new set of forks before you buy them. Carbon fibre, alloy, aluminum is all too weak and ALL fail. Steel is your only option. A magnet will only stick to ferrous material like steel, it won't stick to aluminum, carbon fiber or alloy.

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youngsoulrebel
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Joined: 02/13/2010
Points: 19
Re: Broken Forks

Thanks - others have recommened torque arms too, does anyone have experience with them?

mf70
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Joined: 12/01/2006
Points: 707
Re: Broken Forks

A torque arm would be a good idea. It is basically a strut that runs from a point on the motor away from the axle to a point farther up the fork tube. The are common on many two wheelers; my first bicycle had one for its hub brake.

There's some discussion of it here:

http://visforvoltage.org/forum-topic/bicycles-and-pedelecs/535-doh-just-destroyed-my-crystalyte-motor-and-my-bike

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