Anyone have front hub accidents even with torque arms?

[Recumbent Bicycle Source]

Over 3,000 miles on a Steel Surly Long Haul Trucker and a Mac 350 front with a Grin V2 front torque arm and not even the slightest amount of wear on the drop outs - they look perfect, not even scratched paint.

I just finished a build today with an Electra Townie Front Fork (Steel but very thin) and the new Mac 500 Front and I decided to go with a Dual Grin V2 set up. I'm pretty confident no problems will ever happen... that's half and inch of steel now!

But I personally would not run an aluminum fork on the front even with Torque arms and here is why. Years ago on a brand new Trek Diamond Frame Mountain Bike (Shimano LX) I completely sheered off an Aluminum Crank Arm while riding. I was pedaling hard and then my foot just dropped to the ground (Fortunately I id not crash) but still Scary. I learned at that time just how Aluminum is brittle and doesn't give you a warning... steel bends. That was enough for me.

I do however have a Mac 500 on the Rear of a Trek Aluminum Diamond frame with a Rear Grin Torque Arm and no problems at all.

So yeah I've bought a few Grin Torque Arms and can highly recommend them.

 

[justin2]

I know this thread is a bit old, but it is still the best discussion I could find on the topic. I am about to do my first install of 2 torque arms on my front forks, as part of installing my first eBike conversion kit (with the motor in the front wheel hub). The question I am trying to answer is: should the torque arms be attached to the front or back of the forks?

At first I thought this chat solved the probelem, with the consensus being at the back of the forks. The arguement for this is that by attaching to the back, the force from the wheel will work with the torque arms to push the wheel back into the dropouts.

But thinking about this, if the torque arms were there to stop the wheel falling out of the dropouts, then installing the torque arms at the back of the forks makes sense. But that isn't what torque arms are for. They are for guarding against the front half of the droputs snapping or bending.

So wouldn't installing the torque arms at the back then not reduce this force as much? And so if the torque arms are attached to the front of the forks, the force of the wheel will act to push the wheel away from the dropouts, thus reducing the force on the droputs more, as desired?

Really keen to hear others thoughts on this as I am paranoid of my cheap bike snapping under me!

Edit: on further reflection, could this be the right idea: installing torque arms at front or back of forks both provide equal protection from breaking the forks. But installing them at back of fork provides a second level of protection: if the dropouts still break with the torque arms on, if they are attached to back of fork, torque arms will more likely keep wheel in place as forces work to push it into dropouts?

 

[dustNbone]

You'd want to keep the axle in the dropout, because that's where they're the strongest. Ideally nothing moves at all, but that's not really realistic in real world use.

Even the torque arms themselves are going to bend slightly under repeated loading and unloading, and the cutouts in them where they fit over the axle will over time round slightly, so some distortion of the dropouts is pretty much inevitable.

If it lets totally loose one day, and the axle becomes free to spin in the dropouts/torque arms, you really don't want the front wheel to come out of the dropout, that is likely to end in a serious accident.

Vs. needing a new fork and torque arms but still having your face attached to your skull.

 

[justin2]

Thanks dustNbone, agree! So to confirm, your points lead to the conclusion that front wheel torque arms should be attached to the back of the forks, right?

 

[dustNbone]

I would feel safer that way for sure. I think if you install dual torque arms properly you've got nothing to worry about with a reasonably sized motor.

 

[neptronix]

I've seen tons of front suspension fork breaks on this forum. With torque arms.
Steel is the only way.

Another danger is front traction issues. A front motor is similar to a rear wheel drive truck. All the weight of the truck is on the front without a load, so the rear wheels are slippery.

Except in this case, ~70% of your weight is on the rear wheel, and your drive wheel is also your steering wheel.

I've had a ~800w 700c front motor bike experience wheel slip under power when unexpectedly hitting sand during a turn, which threw me off the bike. After that, i never built a front motor bike again. I also didn't like the weird feel of steering it added.

 

[justin2]

Thanks dustNbone!

 

[dustNbone]

I've had a ~800w 700c front motor bike experience wheel slip under power when unexpectedly hitting sand during a turn, which threw me off the bike. After that, i never built a front motor bike again. I also didn't like the weird feel of steering it added.

I 100% agree with this though. Front wheel drive on a bike is not a good idea, if it can at all be avoided.

It's not really static weight distribution that's the problem, it's the dynamic weight transfer that occurs when you accelerate, which causes your weight to shift to the rear and off the front wheel. This effect is amplified on a bike by the fact that you need to pull back on the handlebars to pull your weight back toward the front wheel.