Big Tom
10 W
With a eZee 500 watt motor (20" front hub), 52v and a Spinner 300 front fork. Would there be a need or benefit of installing a second torque arm (grin's V3) to match both sides.
Thanks, Tom
Thanks, Tom
Is there a need for 2 torque arms
- Thread starter Big Tom
- Start date
I would say yes on two torque arms on a front hub, but you'll receive some feedback shortly on the downsides and dangers of using a front hub motor with a suspension fork. I can't speak from experience, but I've read the arguments and cautionary stories and they make sense.
lnanek
1 kW
- Joined
- Sep 26, 2022
- Messages
- 450
I think the argument against mounting front motor hubs on suspension forks is that suspension forks are basically two tubes that slide more or less into each other. A motor pulling forward on the bottom tube pulls that tube crooked against the other, preventing sliding, and locking out the suspension.
Maybe it doesn't matter if all you ride is on pavement and you don't need front suspension anyway?
Maybe it doesn't matter if all you ride is on pavement and you don't need front suspension anyway?
Big problem with front hub motors - they want to twist the fork every time you accelerate and decelerate.
Suspension forks were not designed to resist that motion.
If your lower or stanchion tubes are made of aluminum or another material that, if repeatedly bended, fails by snapping, you will one day lose your front wheel at speed.
As for being concerned about dropouts, if you have a 500w motor that doesn't have regen, i'd feel allright about 1 torque arm. But i'd prefer 2 always.
Suspension forks were not designed to resist that motion.
If your lower or stanchion tubes are made of aluminum or another material that, if repeatedly bended, fails by snapping, you will one day lose your front wheel at speed.
As for being concerned about dropouts, if you have a 500w motor that doesn't have regen, i'd feel allright about 1 torque arm. But i'd prefer 2 always.
Well actually.. if this is your fork, then you're in luck.
32mm steel stanchions, magnesium lowers.. i believe these are both resilient to eventual failure from twisting.
Pretty good strength. I wouldn't worry about failure from twisting on a fork like this at low power. 2 torque arms wouldn't hurt.
32mm steel stanchions, magnesium lowers.. i believe these are both resilient to eventual failure from twisting.
Pretty good strength. I wouldn't worry about failure from twisting on a fork like this at low power. 2 torque arms wouldn't hurt.
Chalo
100 TW
Even if you get two torque arms that are so secure and free of lash that they totally prevent you breaking off your fork tips, whenever the motor is applying power, it will bind the fork's suspension movement. And on the process, it will slop out the fork bushings in a hurry.
Use a real fork for this job. It's cheaper than whatever repairs you're signing yourself up for.
Use a real fork for this job. It's cheaper than whatever repairs you're signing yourself up for.
Chalo
100 TW
Magnesium is weaker and less stiff than aluminum. A magnesium wrench would be useless, and that's the kind of job a fork tip is being asked to do when you put a hub motor in it.
But does it shatter/shear before bending after too many wear cycles like aluminum does?
I'm no materials expert but i get the impression that magnesium is somewhere between aluminum and steel in terms of this.
Correct me if i'm wrong.
Last edited:
Chalo
100 TW
"High strength" (relative to other Mg alloys) magnesium is very brittle. Weaker structural alloys can be somewhat ductile. Cast metals are almost always more brittle than forged or wrought versions of the same metals, and fork lowers are cast. I can't guess whether typical aluminum fork lowers are more or less likely to snap off than typical magnesium ones, but I am certain that a steel axle would have an easier time carving its threads through mag fork tips.
This subject has been extravagantly discussed numerous times, most recently here:
endless-sphere.com
Front suspension fork dropout failure sets up an especially nasty accident scenario to the rider. You must take all reasonable precautions. Two high quality TAs at a minimum, IMHO.
Torque arm on a suspension fork?
Hi folks, First post here! I've done a bit of digging in previous threads but can't find the answer, so here's my question: is there anything inherently wrong with using a torque arm on a suspension fork? Backstory: I converted my Priority Onyx into an e-bike via Grin's ready-to-roll (front...
endless-sphere.com
Front suspension fork dropout failure sets up an especially nasty accident scenario to the rider. You must take all reasonable precautions. Two high quality TAs at a minimum, IMHO.
DanGT86
100 kW
Arent braking forces on a fork 10x what a motor will produce? The caliper mount is on the lower and the weight of me and the bike are on the upper. Seems like fork bushings are made precisely for these type of forces.
Chalo
100 TW
The fork telescopics are aligned with an approximate vector of rider weight + bump forces + braking forces. It's very oblique to propulsive forces from a hub motor.
Braking forces don't twist the axle.
Want front suspension? Ditch to suspension fork and spring for a Schwalbe 20x2.15 Big apple or the Schwalbe 20x2.40 Super Moto (the latter unfortunately, is becoming difficult to source stateside). Both are verifiably amazing... especially on chip-seal.
DanGT86
100 kW
I can see how hub motors would put a lot of force on the dropouts that they weren't designed for.
I can also see how braking forces are not on the drop out and are not twisting the axle.
The part I am having trouble believing is how braking forces to a bike in motion parallel to the ground would be any different than propulsive forces from a motor as far as the fork bushings are concerned.
Brakes couple the turning wheel to the the fork lowers which then try to rotate with the wheel. This rotation is prevented by the stanchions via the bushings. Hub motors also try to rotate the fork lowers opposite the wheel. This rotation is prevented by the stanchions via the bushings.
Seems like the same exact forces but in opposite directions. My bikes stop harder than they accelerate so I would guess that the braking is actually much harder on bushings than any hub motor's torque.
Not trying to relitigate a timeless argument on here or distract from the thread.
I personally would recommend 2 torque arms on any front hub setup assuming they are properly spaced to not stress the dropout. They consequences of a rear dropout failure and the thin slotted dropouts they generally have when used with hubs make 2 torque arms a must in my opinion.
I can also see how braking forces are not on the drop out and are not twisting the axle.
The part I am having trouble believing is how braking forces to a bike in motion parallel to the ground would be any different than propulsive forces from a motor as far as the fork bushings are concerned.
Brakes couple the turning wheel to the the fork lowers which then try to rotate with the wheel. This rotation is prevented by the stanchions via the bushings. Hub motors also try to rotate the fork lowers opposite the wheel. This rotation is prevented by the stanchions via the bushings.
Seems like the same exact forces but in opposite directions. My bikes stop harder than they accelerate so I would guess that the braking is actually much harder on bushings than any hub motor's torque.
Not trying to relitigate a timeless argument on here or distract from the thread.
I personally would recommend 2 torque arms on any front hub setup assuming they are properly spaced to not stress the dropout. They consequences of a rear dropout failure and the thin slotted dropouts they generally have when used with hubs make 2 torque arms a must in my opinion.
Big Tom
10 W
I currently have a front wheel hub on a Hase Lepus Comfort (delta trike) with a 16" wheel. I normally use Big Apple tires (have difficulty sourcing them most times) and I have found that most times when on longer rides I wished I had more suspension. Longer rides I had started to not really enjoy the ride. My front wheel is not loaded with any weight so it is not any weight related roughness.
This is why I did choose suspension.
Big Tom
10 W
I have done a lot of research and reading, learning. There are a vast differences of opinions and most of those are quite different and those people are very sure that their opinion is correct.
I personally was worried about the torque factor applied onto the stanchions. I understand that the torque of the motor will cause even steel forks to deform, causing "spin out". It is a given that a torque arm should be used for "ALL" electric assist hub motors..... it is always better safe then sorry. I will only use quality torque arms so it should be sufficient to limit "spin out". What I wasn't sure of was if a second torque arm was needed or overboard. I am not sure if I want to disable or cut the wiring to apply the second torque arm.
Tom
I personally was worried about the torque factor applied onto the stanchions. I understand that the torque of the motor will cause even steel forks to deform, causing "spin out". It is a given that a torque arm should be used for "ALL" electric assist hub motors..... it is always better safe then sorry. I will only use quality torque arms so it should be sufficient to limit "spin out". What I wasn't sure of was if a second torque arm was needed or overboard. I am not sure if I want to disable or cut the wiring to apply the second torque arm.
Tom
999zip999
100 TW
? Does a disc front brake on the left side when applied put a twisting force on front forks. Especially the cheap ones
DanGT86
100 kW
I believe it does. I have an old marzocchi fork from the early 2000s with 9mm slotted drop outs. When I brake hard the 2.5" wide tire leans over and rubs the lower.
I do not see how the single sided braking action could not apply a twisting force to the lower.
I do not see how the single sided braking action could not apply a twisting force to the lower.
I believe it does too. Forks have a rating for what size disc they can take because too much torque over time could snap them otherwise.
The larger the wheel, the less torque is produced during braking. This is good, because the suspension fork gets longer as the wheel gets bigger. This can cancel out the additional twist of the bigger fork legs. But it doesn't cancel out the twist from the hub motor.
In this situation i would keep it to about 500w and run two torque arms. The last part of my bike i want to fail is my front fork.
I would be a lot less reserved about a steel or chromoly fork.
The larger the wheel, the less torque is produced during braking. This is good, because the suspension fork gets longer as the wheel gets bigger. This can cancel out the additional twist of the bigger fork legs. But it doesn't cancel out the twist from the hub motor.
In this situation i would keep it to about 500w and run two torque arms. The last part of my bike i want to fail is my front fork.
I would be a lot less reserved about a steel or chromoly fork.
tomjasz
1 GW
Always 2, and alls good with suspension forks with a calm rider, Gonna bang on that throttle? Bad juju.
Isn't that why the thru-axle wheel hubs came to the market?
Perhaps partly correct, stiffening everything up....
Disc Brakes: Advantages of QR, Thru-Axle Designs
Editor’s Note: Today’s QT – in the form of a question from Premium Member Jim O’Donnell and answer from tech guru Jim Langley – covers a couple of different issues regarding road bikes equipped with disc brakes. Namely, it briefly addresses the differences between quick release and thru-axle...
www.roadbikerider.com
Last edited:
Chalo
100 TW
It was to keep the wheel from shifting in or ejecting from the fork tip slot due to braking forces. Through axle doesn't make any difference in the asymmetrical forces applied to the fork when braking.
Similar threads
