Aluminum forks can BREAK!!

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reikiman's picture
Last seen: 2 years 1 month ago
Joined: Sunday, November 19, 2006 - 17:52
Points: 8447
Aluminum forks can BREAK!!

Something that's relatively well known but worth repeating again and again...

Aluminum forks do not mix well with hub motors, especially the more powerful ones. I hope someone can weigh in with more detailed explanation but I have heard this warning repeated several times and heard of a few instances where forks have broken. I've heard of one person whose fork broke while riding and he broke his collar bone.

I installed an front wheel E-BikeKit on my Electra Townie to replace the old Wilderness Energy kit ... it's a fantastic kit, BTW. The kit comes with a torque arm which I dutifully installed. I went to check the install and that was going to require pulling the motor/wheel and discovered that the dropout on the fork had broken. (picture below)

I was sure I'd checked that this bicycle had steel forks. But --well-- they weren't. One way to check is to read the side of the fork, and maybe the manufacturer would have written "Aluminum" on the side of the fork. In this case the manufacturer had written "Aluminum" on the fork, so obviously I missed something in basic reading comprehension. The other way to check is - does a magnet stick to the metal. If it's steel the magnet sticks, if it's aluminum the magnet won't stick.

Fortunately this did not break while riding the bike. Thank you universe for ensuring it did not break while riding.


robert93's picture
Last seen: 3 years 6 months ago
Joined: Thursday, August 13, 2009 - 12:28
Points: 240
Re: Aluminum forks can BREAK!!

Wow!!! you dodged a bullet there! Yes, aluminum while lighter, is more subject to weakening as it is softer than steel. Aluminum can be heat treated to increase its rigidity, but that is best left to professionals, and even then, it does not really allow it to carry more weight, but just assures uniformity of tensile strength. Aluminum is also not forgiving of being bent.
This is also the scary part about people putting front motors on Easy Racers recumbents. Their forks are already under stress because of the design, and have had reported failures without motors added, but only on certain fork designs. (Easy Racers bikes are wonderful handbuilt American bikes, by the way) If a hub motor requires fork mods, I'd strongly consider either a different kit, or a fork that can accomodate the motor design without being worked.

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