How many people run torque arms on the rear

[dougnutz]

This question is probably a little n00b ish but I was curious how many people run torque arms on the rear? I did a little bit of searching already and it seems that 99% of the discussions around TA's are talking about the front. In the few cases where people talk about the rear they are usually using lots of power.

For myself I plan to add TA's to both sides on the rear but at the moment I am just running just one on one side. My dropouts are aluminum but they are pretty thick and the axle has to be tapped into place (tight fit). I'm running a fairly typical 48v setup with current limited to 20 amps. I'm not really happy with my current setup and plan to build some custom arms after I get the disc brakes installed.



I'm really curious what other people have found to be "safe" for the rear. The last thing I want to do is damage the frame.

 

[slimbeau]

i have one running 48 starting today

 

[icecube57]

Im running one but I got an X5 with almost 4kw soon to be 5kw. Which by Endless-Sphere law is mandated that I use one and I still dont think its enough. Like Nike says. JUST DO IT!

 

[amberwolf]

Let's just say that a well-designed and properly-installed pair of torque arms on any hubmotor, regardless of frame type or placement, is safer than not having them. Maybe you'll never need them, but if they're there and you do, nothing happens. If they're not, and you do, bad things happen. Sometimes very bad.

So...as he said--just do it.

 

[docnjoj]

I've got one on my rear steel 9C @ 54 volts and 2 on my wife's front steel fork @ 36 volts. ER bills are much more costly than torque arms!
otherDoc

 

[thewmatusmoloki]

Iv'e put together six ebikes over the years and I put torque arms on the lot of 'em from high to low powered.
Mainly becuse of :

Im running one but I got an X5 with almost 4kw soon to be 5kw. Which by Endless-Sphere law is mandated that I use one and I still dont think its enough. Like Nike says. JUST DO IT!

Which has surely got to go down as one of the ten commandments of ebikes, I dunno , maybe number 2, wadda ya reckon?

8)

 

[dogman dan]

Don't have em on the rear of my steel framed bikes running 48v 20 amps. In one case, the dropouts are at least 1/4" thick. Proper attention is paid to the fit, no cockeyed washers with air gaps under them, etc. No problems because I don't create any with poorly fitting nuts, washers, and axles. Properly fitted, tight stays tight. No regen working on the nuts though.

Mandatory for all bikes of any power lever on aluminum dropouts. It's common sense that a slip on a steel bike bends it some, but on alloy it simply ruins the bike. Both sides!


Almost finished with my pinch dropout for the 2400 watt dirt bike. Mongoose blackcomb steel rear dropouts, but above 1200 watts, I'm going torque arm, in the form of a pinch dropout on one side. Pics soon. Simple design as always from me. two pieces of steel angle iorn. One piece bolted to the frame.

We need somebody to manufacture rear torque arm blanks. A sheet of steel about 3" x3" with the hole cut in the middle. The rest would be easy for us, cutting the outside to fit around the frame and derailur, and locating the place to drill bolt holes. Front ones always have the wrong angle, except for Amped bikes adjustable ones.

 

[thewmatusmoloki]

I too have 6.5mm close fitting steel rear drop outs and yet still have always fitted a 6mm steel torque arm to at least one side.
I only run 2kw or so and agree that I probably don't need them, it gives me over engineered "piece of mind" though dogman,

I seem to remember you being a "no torque arm in the front hub motor" advocate for some time....... :wink:

 

[John in CR]

I don't use torque arms, but that's only because the homemade dropouts on my bikes are steel at least 1/2" thick on each side, and I make the dropouts to tightly fit the hubmotor axle. It may be overkill but not by a lot. My 1200W rated hubmotors that I run at 5kw+ are made to go on steel framed small electric motorcycles in China, and they come from the factory with a 5mm thick torque arm for each side. That's 5mm plus 4 or 5mm thick steel dropouts all designed specifically for the twisting force of a hub motor. I doubt the Chinese would include them if they didn't believe they were necessary.

Bicycle dropouts, steel or AL, are not designed to hold a twisting force. The only bike parts that do apply a twisting force at the axle are coaster brakes and geared hubs, and guess what? They both have torque arms to attach the the chain stay a distance from the axle to hold back that twisting force at a much greater radius from the center of the axle, 80-100mm vs the 5mm radius of the axle flats on your hub motor.

Aluminum is a special case because it fails differently than steel, and generally without warning. It is also subject to fatigue failure much different than steel, so what might be strong enough now may not be after a few hundred twists of that throttle. The primary forces a bike frame is designed for are in the vertical direction, not a twisting force of the axle, and look how much AL is there in the vertical direction, at least an inch high by about 7mm thick judging from your picture.

Think of the force applied at the tire of your bike to make you and the bike move. All of that force is transferred to the bike at the hubmotor axle and to some extent through the surface contact of the axle nuts. If you have a 26" wheel, then due to leverage, the force at the axle flats is over 60 times greater.

To answer your thread topic question, anyone who thinks it through.

John

 

[thewmatusmoloki]

The "pinch type" dropouts that several people on ES seem to have independently developed, especially you John, is helping to push hub motors into the future. Commendable.

 

[John in CR]

The "pinch type" dropouts that several people on ES seem to have independently developed, especially you John, is helping to push hub motors into the future. Commendable.

Thanks. Hopefully someone runs with the concept and starts producing a clamping type of torque arm to sell to those without metal working capacity. I need to take the motor off of my daily rider for the first time in 23 months to change the brake shoes and maybe the tire. I should upgrade those dropouts to a clamping type while I have the motor off.

John

 

[Doctorbass]

The answer is simple!

The first time you taste the fun of electric bike, you'll always want more power!! :wink: IT'S A FACT!!

Than... the need of torque arm become a must!! unless you use these noisy RC motor gearbox and begin breaking chains..

Doc

 

[dougnutz]

I see. But maybe I wasn't clear, I am running 1 torque arm. (see pic) though I am not particularly happy with the fit, I also don't use regen, yet.

I plan to upgrade the brakes to disc brakes and then I will be building something custom in order to make a more perminant solution for the rear. Based on all the feedback here I will probably add a second TA to the other side.

I'm suprised that most of the TA's for sale are for the front, is that because front hubs are more problematic?

 

[dogman dan]

I ran no torque arm on steel front suspension forks for years. 800 watts too! whoo hoo! So yeah, on those cheap but strong forks, no need for 800 watts. the supplied torque washers were used though.

The results when the front wheel leaves the bike caused the invention of torque arms. Personally, I just wish they'd reinvent the motor axle. And eliminate the problematic flat axle design altogether. Heinzmann is the only one I've seen that got it right.

Btw dognuts, I think the way you have your torque arm installed is pretty much decorative. I can't see it providing much resistance the way it is now. But better than nothing, and I bet it's even worse a fit facing forward.

 

[John in CR]

Flipped over I thought it might fit better attached to the seat stay instead.

 

[dougnutz]

Btw dognuts, I think the way you have your torque arm installed is pretty much decorative. I can't see it providing much resistance the way it is now. But better than nothing, and I bet it's even worse a fit facing forward.

I struggled with getting this thing on. There was 4 possibilities per side and none of them actually fit. Adding it this way seemed to "reduce" the tendency to twist, or maybe I am just telling myself that...

As I said before I am not happy with it and plan to replace it, but I was hoping this was good enough for a while. And Really hoping it was more than just decorative

So it looks like I'll be doing some metal fab this weekend.

ps dognuts != dougnutz