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e-Bike Motor Snapped Front Fork Dropout

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e-Bike Motor Snapped Front Fork Dropout

Old 04-02-16, 02:43 PM
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FrenchFit 
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e-Bike Motor Snapped Front Fork Dropout

No longer an alarmist myth for me; very slight incline, sitting on the bike to drive it into the garage from a standstill - hit the button and BAM!, snapped the dropout into two pieces, front of the bike collapsed right but the left drop-out held. Sorta shocking

Would have been catastrophic crash at speed; obviously applying power from standstill triggered the failure but I bet my wife does exactly the same crossing intersections.

10 year old Hi-Ten fork, three year old 250w Hilltopper hub motor, and no torque arms. Lesson learned, glad it was learned at 1 mph in the driveway.

Torque arms on order.
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Old 04-02-16, 03:41 PM
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350htrr
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WOW, and it was only a 250 watt motor...
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Old 04-02-16, 05:06 PM
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All I can say is, "interesting." And here I was thinking that I went overboard with two torque arms on my 350W front motor.
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Old 04-02-16, 06:42 PM
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And here I go putting a 500W on a chrome-moly fork next month. Guess I better put on a torque arm or two.

Edited in 2020. I ended up putting a 250W motor (max draw is about 400W) on an alloy front fork with two torque arms, but I think I will switch to a mid drive.

Last edited by Doc_Wui; 04-13-20 at 12:06 PM.
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Old 04-02-16, 09:28 PM
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Incredible that steel fork failed without warning. Scary; I have a torque arm on my 350w, 36V system on a Surly chromoly fork. Hope for the best. Thanks for the info; cautionary tale.
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Old 04-02-16, 10:03 PM
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I agree that it's a surprise that this happened with a steel fork. This may be of interest on the subject, but specific types of heat treatment can make steel very hard but brittle. Overall though, I would often assume steel would bend instead of fracture or shatter. Any chance frenchie could put a magnet up against the fork to verify the material to some degree?

I've heard of peoples aluminum frames failing while riding retrofit ebikes even with torque arms. Food for thought on when considering your next retro fit.

https://www.youtube.com/watch?v=ulfCxDsVTWo This is a great video on heat treatment of steel if anyone is interested.
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Old 04-04-16, 09:39 AM
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It is a head scratcher for me. I examined the drop-outs, (It turns out the left shattered as well), they appear to be slightly powdery'chalky a the failure points, more like I might expect to Al to look after a crack failure. But against a magnet, the fork is clearly magnetic, ferrous. But testing the failed drop-outs, they don't appear to respond to a magnet. Would Giant have been crazy enough to use Hi-Ten forks with Al drop-outs? In any case they clearly shattered, there is no deformity whatsoever.
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Old 04-04-16, 10:53 AM
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Agree it's a head scratcher since how did they bond steel and non-ferrous and why on a cheap (say that since it's hi-ten) fork. Amazing, but count your lucky stars this time. Can you tell if it looks like the dropouts were swedged (sp?) to the fork tips?
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Old 04-04-16, 02:57 PM
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I don't know what I'm looking at for sure. The bottom end of the fork looks it came out of some hi-tech mold, the entire fork seems uniform, fancy curves & cut-outs, with no sign of welds whatsoever. It's a two piece fork with old type spring suspension in the bottom. My current theory is the Crown & Tube are Hi-Ten, the Stanchions are Chromed steel, and the Lowers & Drop-outs are Al. I wondering if the springs in the lowers are what's offering a magnetic reaction. I'm thinking Giant specing this as a Hi-Ten fork was a tad mis-leading....they were referring to the crown and steerer tube. ?

As I said, the set-up is few years old, and I inspected for cracks and play in the fork assembly from time to time. No issues, and perhaps that makes it a little scarier that it failed with zero warnings.
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Old 04-04-16, 04:41 PM
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Didn't know it was a suspension fork; then good chance lowers were aluminum. Did you have "C" washers for the "lawyer's lips"? Sounds like it was a disaster waiting to happen now.
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Old 04-12-20, 08:04 PM
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Thank you for posting this, with my wheel I will be ordering 2 of these for my bike too. Better safe than sorry.
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Old 04-13-20, 06:51 AM
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Originally Posted by 2old View Post
Incredible that steel fork failed without warning.
Not incredible. Although probability is low, knowing that a lot of forks were not designed for the torque loads of motors or disk brakes, one should not be surprised when this happens.

To the OP: I am really glad that this incident did not result in an injury.
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Old 04-19-20, 09:16 AM
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I started reading this thinking it was solid steel forks but then I thought it was somehow they had crimped aluminium dropouts into steel forks and then at the end it turns out it was suspension forks which to be perfectly honest I would expect to fail at some point especially aluminium lowers. I personally would never have used suspension forks and if I did would definitely have put torque arms on. I feel the case for rigid steel forks with torque arms being the recommended choice for a front hub motor to be safe is still the best advice for sure.
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Old 04-19-20, 10:01 AM
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Agree Bonzo, and the fact the dropouts weren't "magnetic" confirms they weren't steel, so to date, I've never seen a steel fork fail. I've used up to 1500w (30 amp controller, 52V) with a steel front fork (one torque arm) without problems (of course doesn't mean it wouldn't happen). Most of my riding is mid-drive off road, although I built a rear hub for errands recently. FME, 350w, 36V is the optimum for front systems and maybe I'll have another some day (I had a Dillinger, now on my daughter's bike, that was fun both on and off road).
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