Bomber forks.

[Iron Yeti]

Which model/year do you recommend for mounting a geared hub motor on?

Problem is, I friggin' hate my standard gears/dérailleurs etc. etc. I am having so many issues with them, chain falling off, front dérailleur thing keeps rubbing against the chain, constant adjustment, can't shift into certain gears, noisy jarring shifting, I am just going to buy a Nuvinci internally geared hub (Anyone use one? Anyone recommend a model?)

So I am going to mount a motor on the front hub. So I am going to replace my fork with a sturdy bomber fork. Which one to use? Also, suggestion on Nuvinci internally geared hubs.

Thanks.

 

[Alphorget]

I've never used the nuvinci but I have a Shimano Nexus 7-speed hub and I love it. They now make a 8speed hub too.

 

[Drunkskunk]

Imagine you take your fork off your bike, go out to a farmer's pole fence, and stick the fork upside down on the fence by the headset. Now stick a piece of square barstock into the dropout (lets pretend a 10mm piece is just laying around). now find a willing plow horse, in the farmer's field, put a harnes on him, and tie it to the piece of bar stock in the dropout. Now give the horse a swift kick in the butt, and let him pull hard on the fork.

Think it will survive? Thats only 745 watts of force. 1 horse power. Litterly. the equivilent of a 36 volt battery and 20 amp controller.

But thats not realy the weak point. For that we need to realy stress the dropouts.

Imagine taking a 1 foot long bar, and welding it in a T shape to the square bar you put in the dropouts. (1 foot because thats roughly the leingth between the hum and the ground when you include a rim and tire.) Now, put that T bar back in the dropouts of the fork, with the bar sticking straight up at the sky. Hitch the horse back up, and let him pull. Think those aluminum dropouts are strong enough to survive the twisting force of the horse? Thats how much force is on them at startup.


Sure, you can make it work. It is possable to beef them up, but not easily, and not without some technicle skills.

 

[lostcoyote]

i have the same issue on my bike. the front forks are bombers which rules out a front hub motor.... and i have a rear cluster 9 speed.

it's either replace the front forks or drop down to a 7 gear cluster.

just about all front suspension forks are aluminum these days - can ya point me to one made of a steel alloy?
maybe going to a 7 speed cluster's the better choice?
maybe i should leave my high end mountain bike alone and get a new bike for conversion purposes as someone had suggested yesterday.

 

[jimmyg4life]

I guess I was lucky I have an older Huffy Verdict and the shocks are steel and actually have a motorcycle type upper and lower triple tree fork set up and works great with my 48 volt front hub.
Good luck but you really are forced to go rear hub motor with dual suspension these day cause of the aluminum shocks

 

[John in CR]

To me only the dropouts are an issue. The top of the shocks are designed for the high forces of braking, though I still inspect the headset and shocks regularly for early warning signs. My dropout solution was to cut the AL dropout off and make new ones out of a thick piece of steel cut into an "L" shape. I cut new dropouts into the bottom of the L, and welded the top of the L to thin steel tubing. The tubing is slit up the length on one side to accommodate any shock. Just slide it in and clamp. The L essentially becomes a one piece torque arm and dropout welded to a prosthetic sleeve to fit on any shock. Sorry my camera is on the fritz, so no pics.

John

 

[Lock]

Thats only 745 watts of force. 1 horse power. Litterly.

Had to check that...
seen here:
http://en.wikipedia.org/wiki/Horsepower#History_of_the_term_.22horsepower.22

"R. D. Stevenson and R. J. Wasserzug published an article in Nature 364, 195-195 (15 July 1993) calculating the upper limit to an animal's power output. The peak power over a few seconds has been measured to be as high as 14.9 hp. However, for longer periods an average horse produces less than one horsepower."

tks
Lock

 

[lostcoyote]

dumb question #1 - if aluminum forks have problems handling the torque loads, then with a rear hub motor, wouldn't the aluminum frame/dropouts have similar issues with stress?

dumb question #2 - don't torque arms solve this problem or do they only work on the rear?

 

[John in CR]

dumb question #1 - if aluminum forks have problems handling the torque loads, then with a rear hub motor, wouldn't the aluminum frame/dropouts have similar issues with stress?

Absolutely. Front or rear, the aluminum just snaps right off.

dumb question #2 - don't torque rods solve this problem, front or rear?

On the rear you may be able to get the torque arms in good enough alignment with the frame members to be effective, plus you have a lot more AL around the dropout to begin with. On front shocks there's not much metal there to begin with. On my first try, the machine shop talked me into some thin but very strong stainless steel as torque arms. I didn't make it 10 feet on the first ride before the aluminum dropouts snapped right off and the axle spun in the stainless dropouts, not because the stainless failed, but because the torque made the stainless just cut into the axle on both sides. The axle spun ruining the wiring harness, which was a major job to replace. Luckily the torque arms had holes cut out to exactly fit over the axle and they were clamped to the shock, so the wheel couldn't just fall off.

Keep in mind that rewiring a harness really sucks, and a short from a spun axle can blow your controller too. Also, on the front the risk is far greater. If the front wheel comes off, a face plant into the pavement is almost guaranteed even at the slow speeds. I got off lucky. Even though I have an aluminum bike, any motor connected to it will always have a steel connection.

John

 

[dogman dan]

question 1 , Yes , sometimes they do.

question 2, torque arms help, especially in the rear aluminum frames.

question from previous post. Cheap wallmart bikes have 1" headset steel suspension forks that are bad, but good enough for street use with small motors. The clamp on dropouts sound cool, but on many aluminum suspension forks there is still an issue about space for the hubmotor between the tubes. On the steel cheapies, I squash em in a vise till there is room. 1200 miles with no problem with my wallmart forks and a WE motor on 36v.

 

[John in CR]

question from previous post. Cheap wallmart bikes have 1" headset steel suspension forks that are bad, but good enough for street use with small motors. The clamp on dropouts sound cool, but on many aluminum suspension forks there is still an issue about space for the hubmotor between the tubes. On the steel cheapies, I squash em in a vise till there is room.

Dogman,

I welded the new dropouts on the tubes to give me adequate clearance with no need to spread the shocks. I have nuts on both sides of the new dropout to prevent the shocks from moving in and rubbing the motor cover, and I have room on one side to reinstall my disk brake once I attach the disk to the motor cover. My steel cheapie bike has shocks that are closer together, so I'd need to pry them apart or crush them some like you did, both of which may prevent the shock itself from functioning properly, and leaves no room for a disk brake. You bring up an significant consideration. It's not just the dropout width, but also the width between the tubes of the shocks that is also important in fitting a front motor.

John

 

[Drunkskunk]

dumb question #1 - if aluminum forks have problems handling the torque loads, then with a rear hub motor, wouldn't the aluminum frame/dropouts have similar issues with stress?

Yes, but the rear is triangulated. The forces are spread out through the whole frame, and that makes it hundreds of times stronger. I wouldn't use a lightweight roadbike frame, but a heavy aluminum frame should be fine for anything in the sane power range.

dumb question #2 - don't torque arms solve this problem or do they only work on the rear?

They solve the dropout breakage problem only. Building ones for a suspension fork are a little more complicated. Unlike a steel fork, where the torque arm just needs to augment the fork's streingth, on an aluminum fork, it needs to be the primary means of transfering torque from the wheel to the bike frame.

 

[ebinary]

Does all this conversation apply to magnesium too? At least half the good fork lowers are magnesium. Any definitive information here. What little I found seemed to claim that magnesium could absorb vibration (which aluminum cant).

 

[lostcoyote]

so who manufactures steel alloy forks these days?


heck, there's alot of front hub motors out there - something must be working?
otherwise, if there were so many fork failures, they wouldn't make front hub motors it seems.

 

[Mark_A_W]

Imagine you take your fork off your bike, go out to a farmer's pole fence, and stick the fork upside down on the fence by the headset. Now stick a piece of square barstock into the dropout (lets pretend a 10mm piece is just laying around). now find a willing plow horse, in the farmer's field, put a harnes on him, and tie it to the piece of bar stock in the dropout. Now give the horse a swift kick in the butt, and let him pull hard on the fork.

Think it will survive? Thats only 745 watts of force. 1 horse power. Litterly. the equivilent of a 36 volt battery and 20 amp controller.

But thats not realy the weak point. For that we need to realy stress the dropouts.

Imagine taking a 1 foot long bar, and welding it in a T shape to the square bar you put in the dropouts. (1 foot because thats roughly the leingth between the hum and the ground when you include a rim and tire.) Now, put that T bar back in the dropouts of the fork, with the bar sticking straight up at the sky. Hitch the horse back up, and let him pull. Think those aluminum dropouts are strong enough to survive the twisting force of the horse? Thats how much force is on them at startup.


Sure, you can make it work. It is possable to beef them up, but not easily, and not without some technicle skills.

Force is not measured in Watts, in is measured in Newtons, the analogy is incorrect.

And I imagine a horse could pull at least something like 5000N for a few seconds.
"Horsepower" was averaged over a day anyway, and the correct units are Watts/Kilowatts.

It is the TORQUE of the motor, reacted by the dropouts against the axle, that is the issue. Somewhere between 20 and 100 Newton-metres, which isn't insignificant.


Reinforcements are needed, something like these, fitted to 2000 Bomber Junior Ts:

 

[D-Man]

Good luck with geared motor in front suspension! Wear safety gear.

 

[MitchJi]

I am just going to buy a Nuvinci internally geared hub (Anyone use one? Anyone recommend a model?)

Also, suggestion on Nuvinci internally geared hubs.

Thanks.

Hi,

A friend asked me to help him sell 25 NuVinci Hubs. He got them directly from Nuvinci at an OEM price for a small production run of Ebikes that drive through the gears. He really liked for manual use (the way you would be using it). He decided he wanted something that shifted up in regular increments because he could manage his watt usage better (both motor and pedaling were through the Nuvinci).

He has not given me a final price but he tentatively mentioned selling them for what he paid for them which is $300 each and throwing in shipping.

EDIT: He said to sell them for $275 each including shipping in the U.S.

The downsides are its pretty heavy and I think the Nuvinci is slightly less efficient (better after break-in) than geared hubs.

On the plus side it has a wider range (350%) than any hub but the Rohloff and of course the infinite ratios are really nice.

You can get more information by looking at a page I put on the web that describes exactly what he is selling plus links to general NuVinci info:
http://mitchji.home.comcast.net/~mitchji/NuVinci.html

PM me if you have any questions or if you want one.

Thanks!

Mitch