Fork reinforcement ?

[Bouboutrip]

I just broke my front fork with my new 500W motor (first trial) and I know there exist small pieces of equipment that can fit on the tip end of the fork for reinforcement. This is a suspension fork and one of the finger tip that holds the main bolt of the shaft wheel; This is where it went off. Anyone can help me with this?

Thanks.

 

[cdev]

There has been quite a bit of discussion about this problem, especially with suspension forks as they are usually aluminium or magnesium which are not as hard or fatigue resistant as steel. The problem is that the torque generated by the motor has to be transferred to the bike so to do this safely you must fit a torque arm. This torque arm has to transfer all the torque to the forks and so must be a very good fit on the motor axle and must be secured firmly to the forks. The longer the arm the less torque it will apply to the forks so in my opinion the best sort are not the ones that attach to the mudguard mounts but the sort that clamp higher up on the forks. If you do a search for "torque arm" on this forum you should come up with pictures and info about the various types..Good luck

 

[dogman dan]

There have been some that have made great steel dropouts to fit onto aluminum suspension forks. Basicly it's a steel pipe that fits over the fork tube and clamps on somehow, usually attaching to disk brake mounts also, and a strong steel fork from 3/8" sheet is welded onto that. On rear hubs with aluminum frames, the best builds use a custom fabricated torque plate, that also acts as a substitute dropout.

Most people think the torque is the problem when it isn't. The real issue is a poor fit of the oversize hub motor washers and nuts on a quick release fork. The same thing happens to steel forks when the fit is poor. As the washer slowly deforms, the nut gets loose, or the dropout itself may deform. Either way, riding with a loose nut is allways disaster. Torque arms only minimize the damage and do not correct a poor choice of forks.

For a front hub motor, there are few substitutes for a steel fork designed for a bolted on wheel. Bmx and MTB forks with beefy steel dropouts are the best.
I'll never bolt a motor to an aluminum dropout myself, unless the motor designers wise up and integrate the torque arm into the motor, and eliminate the flats on the axle, as heinzmann did.

 

[chet]

"...riding with loose nuts is allways disaster..."

Amen, my friend.

 

[ambroseliao]

If you're new to ebikes, a popular torque arm looks like this:

http://www.e-bikekit.com/shop/index.php?p=product&id=31&parent=3

One of the warnings about fitting a front hub motor is that your forks have to be steel and the motor has to be mounted very solidly (no play) in the dropouts. For me, a torque arm is mandatory to avoid situations like yours.

I hope you didn't get hurt. Go online or to your LBS and pick up a solid steel or cro-moly (steel) front fork. Mount your motor with the torque arm solidly attached to your fork and enjoy the ride!

Ambrose

 

[USAEBIKECO]

For safety I would not ride an ebike without a torque arm. Also, never ride a bike with suspension or aluminum forks if you have a front hub motor. It could suddenly break and send you to the hospital.

Steel forks are much safer for front hub motors.

 

[spinningmagnets]

Another "Aluminum front fork with no torque arm" pic for the files...

 

[dogman dan]

Quick release dropouts on that fork too, which just makes a problem even more likely. We still need the motor redesigned, so the flats of the axle don't put any leverage on the dropouts. There is plenty of evidence that the flat part of the axle just breaks the dropouts, even on steel forks if the nut gets loose. With a smaller diameter axle, the washers would fit, and the wiring can come out of a larger stationary part of the hub.

But it costs more to manufacture, so I'm not holding my breath on it. Meantime fronties need beefy steel dropouts, like bmx forks, or at least big beefy dropouts from bikes with bolt on front wheels.

 

[TylerDurden]

Mark_AW made steel fork-ends:

http://endless-sphere.com/forums/viewtopic.php?f=6&t=1533

 

[Drunkskunk]

Mark_AW's fork has got to be the most reposted pic on the forum. Brilliant piece of engineering too.

 

[chet]

Quick release dropouts on that fork too, which just makes a problem even more likely. We still need the motor redesigned, so the flats of the axle don't put any leverage on the dropouts. There is plenty of evidence that the flat part of the axle just breaks the dropouts, even on steel forks if the nut gets loose. With a smaller diameter axle, the washers would fit, and the wiring can come out of a larger stationary part of the hub.

But it costs more to manufacture, so I'm not holding my breath on it. Meantime fronties need beefy steel dropouts, like bmx forks, or at least big beefy dropouts from bikes with bolt on front wheels.

The Heinzman style torque arm should be mandatory for any thing over 750W.

 

[morph999]

I tend to kick off with my feet and pedal one or two times before hitting the throttle. This helps too. Right? I'm going to keep doing that with my 5303 motor too. It probably helps lessen the torque. I guess though it's not very dangerous when you are only going 3 mph.

 

[dogman dan]

Yes it will, or like I do, I use the trottle right away, but I never mash it right off. I just apply it easy for the first 10 feet, and ease the strain on everything, dropouts, controller, battery.

But nothing can save you if you have poor fitting washers. Either the washer bends or the dropouts bend, and then the loose nuts let the axle break the dropouts. A good fit is 99.9% of running a front hub safely. With loose nuts, 200 watts destroys dropouts easily.

 

[icecube57]

If you want a good solid rigid fork... Look into the Surly forks. The Surly Instigator fork is a direct replacement for bikes that originally had a front shock fork. Its made a little bit longer to maintain original ride height. Im using this with front wheel hub motor with 80-90v with two torque arms... I havent seen any fatigue on it. It flexes with bumps to dampen the bumps but not eliminate them. I paid 74$ delivered. Down side is it has a weird drop out angle which means you need to use a universal any angle fit torque arm.

 

[Crash Machine]

I'm actually in the process of replacing my forks because I'm tired of worrying about it. I've been running aluminum suspension forks but I don't feel comfortable going off-road at all so why have 'em. So I switched to the Surly Instigator rigid steel forks. I am first and foremost a commuter and this will allow me to put on the Surly Nice Rack.
Here's a pic. of what I was using before. I ran like this 1500 miles. I can hear the gasps of horror from here...Here's a side view... Here is a pic. of the new setup. I haven't added the Surly Nice Rack yet. I'll have to drill a hole through the torque arm to mount the rack on the fender eyelet I think... Side view of this...
Does this all look right to anyone else?

 

[dogman dan]

Gasp! all right. The fist pic shows pretty clearly that the washer does not sit correctly on the fork, and is crooked due to the QR lawyer lips that are smaller than the motor hub washers.

Everything looks sweet in the second pic, on the surly fork.

 

[Crash Machine]

What I ended up doing is filing the dropouts a little deeper on the new fork. Actually just enough to make it seat fully and leaving the the lawyers lips on. They weren't as prominant on the steel fork. With the axle sitting fully in the dropouts the washer seats itself right behind the lawyers lips. I had to do this twice because I ended up getting Surly Pugsly forks by mistake. They are made for oversize rims and tires so the brakes didn't line up.The Instigators line up real nice for anyone thinking of getting 'em. The Surly Nice Rack will be here tomorrow. I'm going to mount it behind the torque arm with a bolt that goes all the way through it to the fender mount. Will post picstures. Anyways, I haven't ridden it so I don't know what to expect. I should be able to take it off-road now,maybe? Not jumps or drops or nothing just minimal trail riding. Should be O.K. right?

 

[D-Man]

May not be brilliant idea, but I used glue on my dropouts. :lol:
Supposely made from Bigfoots feet. Sasquatch knows! Its revolutionary.

 

[ambroseliao]

Glue won't help hold the motor to your fork. You need something much stronger than glue! A thick torque arm keyed to your motor's arms is the best solution.

Ambrose

 

[dogman dan]

Proper fit is really the most important issue. The surly forks made that easy.

 

[317537]

Rear hubs rule.

And just think that ebike in three minutes video star did his wheel nuts up with his fingers, with no torque arm on a pair kitten forks.

Some nice torque arm designs above. good work.

 

[icecube57]

Proper fit is really the most important issue. The surly forks made that easy.

Mine was so tight i had to beat my motor in.. after filing. Again the only complaint i have about the Suly fork is the jacked up dropout angle that prevented me from using a regular torque arm in the correct fashion.

 

[torker]

Proper fit is really the most important issue. The surly forks made that easy.

Mine was so tight i had to beat my motor in.. after filing. Again the only complaint i have about the Suly fork is the jacked up dropout angle that prevented me from using a regular torque arm in the correct fashion.

The weird angle was an issue on my easyrider too. Plus I woulda had to spread/ bend the forks on my 700 dollar bike and file the slots wider "and" deal with the lawyerlips. I hope to try a rear hub on it sometime.

 

[Scorefield]

I think I saw that you are using plastic, but I would suggest that you get something that might be better for yours safety maybe.
Almost sure that I saw someone on this forum using a point closed-end wrench for high torque on the fork.

 

[Scorefield]

Found the thread.
http://endless-sphere.com/forums/viewtopic.php?f=2&t=13277&p=197863&hilit=wrench#p197863

This is how I think it should look like, now when anyway most people want torque....it's cheap wich I like.
Credit for the pic. goes to Doc.