Torque Washers and Torque Arms

[ChrisOfBristol]

I've got a mountain bike with aluminium front forks and a 250W motor. The motor shaft has a 4mm long, 12mm diameter step with 10mm flats for Bafang-style torque washers. However I have read elsewhere that on aluminium forks the washer can force apart the dropouts so I should use a torque arm. I'm sure that would be a good idea with a more powerful motor, but I'm not sure with 250W. What is your view?

 

[indianajo]

I'd say change your fork to steel.
You might get away with a torque arm, I've seen no data on the 250 w scenario. What is certain is that if the fork snaps or the wheel falls out of the slot, diving head first to the pavement is a serious problem.
I have a 4" long torque arm. Don't rely on worm hose clamps to hold the torque arm to the fork. Use real non-slotted steel. My clamp band is 3/4" wide x 24 ga steel. I drilled holes for #10 machine screws to hold it.

 

[JRA]

Just keep tolerances as tight as possible and also use flat washers that fit inside the lawyer lips, can't see in the pic but sometimes the top of the dropout needs a little relief from a round file to seat the axle all the way? Can't give you an exact torque # but it should be tight and checked often to make sure it stays that way especially if you have regen. I have used a carbon fiber rigid fork with a torque arm for a system that put out 1300watts with not problem so yes, torque arms are better when you get into higher watt output and heavier loads also.

 

[Marcela]

That looks like an aluminum casting. I'd say no. If it was CNC'd aluminum or stronger steel piece you could be fine. Depends on how the motor behaves of course.

 

[harryS]

You might not have a long enough axle to fit all the pieces, but I would have a second washer that fits into the circular inlay on the fork, a torque arm over it, and then the axle nut.

I have put a 250W motor on an alloy fork, but I used two torque arms. Torqued the nuts down to 22 ft-lbs, marked them with a sharpie and they never moved. Findally one day I came across a bike with a steel fork that used disk brakes, and I ordered the fork.

 

[suenord1]

I used to be in doubt about whether to put the torque arms in front of or behind the forks. I recently took a couple of photos of what might happen if you put your torque arms in front of the steel forks. I think the photos speak for themselves. It was a 500w Bafang motor. I will also show a photo of the new fork and where I placed the torque arms (both sides).

 

[m@Robertson]

@suenord1 frankly those torque arms are junk. They are the Grin Tech v1 that is widely counterfeited and seldom has even remotely tight tolerances at the axle. And even if they do, that torque arm can slip straight down even if you put them on properly. You've figured out the hard way not to put them on backwards; I assume thats a direct drive hub and it came out during regen/deceleration?

@ChrisOfBristol there is some merit to the thought that on only a 250w motor you can get away with torque washers. But not enough to risk your fork, which will be permanently destroyed if you spread the dropouts... which can happen. And on an aluminum fork? Thats playing with fire. The internet is absolutely riddled with photos of alloy dropouts on rigid and (especially) suspension forks that snapped clean off even with dual torque arms. Can you get away with a front 250w rigid fork if you use torque arms? Probably. Should you? No. You should use steel. Do enough research and you'll find more than ample examples not to emulate, and I am including the 250w power level, bearing in mind the wattage rating on a motor is meaningless and what really matters are the Nm of torque they output, which is comparable to much more powerful motors.

I've done many front motors; usually as part of a 2wd system. I've also done alloy forks successfully (so far) and I have ruined steel ones (using the torque arms that @suenord1 used above). What you want to do is eliminate the possibility of a problem because the consequences will be severe and permanent (you'll wrap your motor cable around your axle and about half the time it will tear out of the motor as it wraps). Since you have an alloy fork and thats that (and it looks like a nicely snug fit that I hope came naturally, you should

1. Use TWO torque arms. Yes I know that doubles the cost. Compare that to a faceplant and a new fork. You want overkill here.
2. Do not under ANY circumstances file the dropouts so the axle fits centered in the dropout. If you have already done this, go get another fork and try again. Filed dropouts snap off. Especially alloy ones. There are other ways to deal with the lawyer lips on a fork besides grinding off material crucial to structural integrity.
3. If you can, use torque arms that move the point of contact up and away from the dropout. It looks like you have to do this since you have no fender eyelets. On an alloy fork with low power two eyelet type Grin V2 stainless arms would be plenty. Instead probably you are looking at something like a Grin V3 that has multiple anchor points on the fork.
4. If you are doing two torque arms, its fine to use them both on the back side so long as you are not using regen on a direct drive motor. If you are, it has to be behind on the right side and ahead on the left. If its a geared hub just put them both behind and you'll be fine.

Torque Arms - Grin Products - Product Info

For every force there is an equal and opposite force, and for every torque there is an equal and opposite torque. Sadly with import hub motors this opposing torque is often born entirely by bicycle dropouts that are not up to the task, allowing the motor axle to spin out. Grin has pioneered the...

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[suenord1]

It was a 500 watt Bafang geared motor, the same as I have used on about 8 e-bikes. The dropouts failed in the first 5 feet, under very low acceleration. I did not even get out of the driveway. I know the copied torque arms are junk, but they were all I had. I have never had a wheel fall off like that on any other ebikes I built. The forks on that tricycle were were absolute trash. I have 2 tricycles and 2 bicycles in my garage. I hope the torque arms are on the back of the forks, but I will certainly check before using them again. I just hope my photos will make some people think twice about mounting them on the front of the forks. Thank you for commenting!

 

[harryS]

Well, it's good you did not crash and faceplant, Sue. Steel forks too. Wow.
.
What you folks using for torque, if you're using torque wrenches? I'm around 25 ft-lbs on the front motors. Did it by feel on the rear motors and found I was low 20's.


.

 

[indianajo]

I used to be in doubt about whether to put the torque arms in front of or behind the forks. I recently took a couple of photos of what might happen if you put your torque arms in front of the steel forks.

I see you didn't believe me about not using a worm hose clamp.
My 4" long torque arm is on the front of the front fork. It is a single. The 24 ga x 1" locator band doesn't wiggle. The oblong holes in the arm for the axle are custom filed and fit the motor axle tightly. 8000 miles, no problem. I've worn out a 1300 w geared hub motor and rain destroyed a 1000 w Mac12t hub motor.(harness). Now I have 500 w bafang. which is wimpy.

 

[suenord1]

Well, it's good you did not crash and faceplant, Sue. Steel forks too. Wow.
.
What you folks using for torque, if you're using torque wrenches? I'm around 25 ft-lbs on the front motors. Did it by feel on the rear motors and found I was low 20's.


.

Yep. That was too close. I guess a torque wrench should be next on my shopping list, along with some Grin Technologies torque arms. I was just visiting in the US.

I see you didn't believe me about not using a worm hose clamp.
My 4" long torque arm is on the front of the front fork. It is a single. The 24 ga x 1" locator band doesn't wiggle. The oblong holes in the arm for the axle are custom filed and fit the motor axle tightly. 8000 miles, no problem. I've worn out a 1300 w geared hub motor and rain destroyed a 1000 w Mac12t hub motor.(harness). Now I have 500 w bafang. which is wimpy.

Actually, I have never heard of a worm hose clamp. They sound stronger than a simple hose clamp. I will try them. I never had the front of a dropout bend straight out like that before either.

 

[tomjasz]

I have never heard of a worm hose clamp.

It’s worm gear hose clamp. The screw inside the housing that tightens the slotted band is a worm gear.
Dual Grin, not Grin style torque arms and ordinary hose clamps are fine.

 

[indianajo]

Actually, I have never heard of a worm hose clamp. They sound stronger than a simple hose clamp. I

You have 3 pictures of them in post # 6. The slots for the screw destroy the tensile strength of the steel. My clamps have through holes for #10 (US) or 5 mm SS screws. I use elastic stop nuts so they stay tight. Mcmaster.com or grainger.com .

 

[tomjasz]

 

[suenord1]

You have 3 pictures of them in post # 6. The slots for the screw destroy the tensile strength of the steel. My clamps have through holes for #10 (US) or 5 mm SS screws. I use elastic stop nuts so they stay tight. Mcmaster.com or grainger.com .

Oh, sorry! I missunderstood. Clamps without all the slots would obviously be stronger. I will look into that.

 

[tomjasz]

Oh, sorry! I missunderstood. Clamps without all the slots would obviously be stronger. I will look into that.

Bullshit

 

[suenord1]

Bullshit

I really did missunderstand. They are called slangeklemmer where I have lived the last 42 years.

 

[m@Robertson]

I really did missunderstand. They are called slangeklemmer where I have lived the last 42 years.

I don't think he was commenting on the veracity of your statement. I think it was more like the clamps with or without slots are more than enough in terms of their raw strength versus any alternative. The issue is not the hose clamp, its the overall design of those clones that allows some slop and motion in the clamp (especially at the hose clamp point on the V1 clone), which in turn lets them fail.

A pair of lets say Grin v3 clamps, secured by three hose clamps, not just one, and you'd be giving that axle and the dropout a lot of support. Especially considering we're only talking a 45-60Nm motor.

Something else to also consider... Again I'm coming from the direction of using two clamps here: there's no law that says they have to be the same type of clamp on each side. You have a disk brake mount on one side and that mount can be used to bolt on a clamp.

I dug into my archives. This one is from early 2017. Its half Grin v2 around the axle, and half of another UK manufactured torque arm (go to Ebay and search for 'bicycle torque arm'. Among the many Chinesium ones there is a company there selling them). What its doing is using a longer bolt on the brake mount instead of the short hop up to the dropout eyelet. Since you have no eyelets, this is a viable option for you (for me it helps to have a lot of spare parts in the garage so I can mix/match this sort of thing). Doing it this way lets me do completely without any sort of hose clamp, and the anchor bolt is a nice beefy M6 bolt. This is an 80 Nm motor tied to a 35a controller on a 52v system. So it is more than capable of ruining a steel fork.

this link goes to that UK ebay seller. This is a variation on what I did above where the axle clamp can be given any position, which makes it easier to set up the clamp the way I did above, where the whole thing is bolted in at full-extension already and can't slip to a (catastrophically) more extended length. On the other side I used a Grin v2 and connected to the eyelet.

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This one has a different sort of brake mount arm that can be bolted down with no chance of slippage in two different places.

Torque Arm universal Kit axle 10x12,10х14 mm heavy Dropout Amplifier E-bike Hub | eBay

Need use with powerful motor wheel, gear hub from 1000 w and more.,in set universal arms, 2 universal adapters 14 and 12 mm. Made from hardened steel solid steel, 4-4,2 mm. Torque Arm universal Kit axle 10x12 and 10х14 mm heavy duty Universal Dropout Amplifier for E-bike Hub Motor.

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[indianajo]

The issue is not the hose clamp, its the overall design of those clones that allows some slop and motion in the clamp (especially at the hose clamp point on the V1 clone), which in turn lets them fail.

I disagree. I've seen a picture of a Mac motor with the worm clamp all stretched out & the wire twisted off. My clamp is 1"x6"x22 ga solid steel cut out of an old appliance. I deburred it and drilled 3 holes in it. Fold over strut and attach to the arm, which is 1"x4"x12 ga steel cut drilled & filed out of bed frame rail.

 

[tomjasz]

I disagree. I've seen a picture of a Mac motor with the worm clamp all stretched out & the wire twisted off. My clamp is 1"x6"x22 ga solid steel cut out of an old appliance. I deburred it and drilled 3 holes in it. Fold over strut and attach to the arm, which is 1"x4"x12 ga steel cut drilled & filed out of bed frame rail.

I saw a picture of a Martian… Come on jo ya gotta do better than that… Didn’t you kill your Mac long before you wore it out?