Mac 12T and dual torque arms -> really necessary ?

Hi there,

I am running a 12T MAC on my E-MTB combined with a KT36 20 Amps controller. Following the guidelines / suggestions both from Grin and EBS (www.ebike-solutions.com) I have used dual torque arms like those:
http://www.ebikes.ca/shop/electric-bicycle-parts/torque-arms/torqarm-v4.html



On Sunday I had a flat tire in the rear and needed to disassemble both torque arms somewhere in the wild.

While removing the torque arms with the required tools is not exactly rocket sience, it still takes 5-10 minutes on top compare to fixing a flat tire in the front.

This kept me thinking on my way home:
- Do I really need dual torque arms ?
- Wouldn't one torque arm be sufficient ?
- Should I design an open torque arm from 5-6 mm steel for one side ? Similar to a reinforced dropout ?

As for the open torque arm I could imagine something for the left side screwed to the disc brake mounting holes.

What do you think ?

BTW: I am aware that a spinning hub axles will screw up my dropouts and hence my MTB frame. While I am more a "better safe than sorry" kind of guy, I still could live with some higher risk if this means more convinience for changing a flat tire / tube.

TIA,
Holger

Why not use a puncture repair kit/patch, then you wouldn't need to remove the wheel at all?

Well, simply because it is sometimes hard to relocate both the hole in the tube and the possible cause of the flat inside the tire ?
Fiddling around inside an tire while the wheel is still in its place is somewhat a PITA to me.

If your torque arm is well fitted and strong, one should do the job. But put it on the solid end of the axle. The hollow end of the axle has much less structural integrity and really only serves as a backup in case there is some failure of the torque retention on the other side.

@Chalo: Thanks for clarification ! :thumb:

So for me this translates to:
I can easily get rid of the torque arm on the left side if the right side is fitting snugly enough. This would at least reduce the number of torque arms to remove by 50%. :wink:

What is still unclear to me: Would two enhanced dropouts (in other words a 5-6 mm steel plates which mimic the shape of the original dropout with an opening for the axles) be strong enough to take the torque of the Mac ?
Because this would mean no torque arms at all which need to be removed.

You are focusing on the wrong issue, rather than wishing for an easier way to repair a flat, you should be thinking about what you can do to prevent flats.
During the 8 years that I have been building and riding Ebikes, the evolution of my wheels and tires has received more attention than any other element.
Partially because I ride in a desert with lots of organic hazards to bicycle tires, my first several years were plagued w/ flats and I tried many things including tire liners and sealants. But the best solution came from using the highest quality, flat-resistant tires and extra thick tubes.
It's hard to tell from your pic, but that tire doesn't look like anything special. I would strongly suggest you look into tires w/ a "flat-guard" band. I have used Schwalbe Marathon and Marathon Plus tires as well as the budget Forte copies, but these days prefer the WTB "Slick" series. The Fortes did not have enough quality control and I have had a couple that self-destructed, but they offer a great extra thick tube.
The only down-side to this approach, aside from a slightly higher purchase price, is the thicker thread imparts a slight "squirmy" feeling. Add an extra thick tube and it can be a little un-nerving. That's why I like the WTB, the flat-guard band is not as thick and they feel a little more stable.
At any rate, one gets used to the feeling and it is a sm. price to pay, to greatly reduce, if not eliminate flats.
You torque arm installations look good and to remove one, especially since it has already been fitted would, IMO, be a mistake.

Well, how many volts are you running?

You might be able to get away with a single torque arm if this is the freewheel version with the regular 14mm axles.
If this is the cassette version with 12mm axles.. i'd strongly suggest a pair of torque arms on even 750w peak power.

I second the 'puncture resistant' tires comment from motomech. I run the highest puncture resistant tire from Schwalbe i can get at a bare minimum. Goathead thorns plague me so bad here in Utah that even those tires are not enough.

motomech said:

but these days prefer the WTB "Thick Slick" series.

Click to expand...

ThickSlick Flat Guard is the best tire we're using these days on pedicabs. Some of the drivers can't exercise their heads enough to accept slicks, so we also use Cruz Flat Guard.

HolgiB said:

....with a KT36 20 Amps controller.
- Do I really need dual torque arms ?

Click to expand...

Basically what neppy said above - two would be the best situation...

But - regardless of voltage, your 20A controller is probably only going to provide 50 phase amps which is not really driving the Mac hard so you don't have an especially bad torque situation just because it's geared. If you plan on getting a more aggressive controller, then two TA's look much better.

That said, the TA should be no thinner than 1/4" (6mm) thick like the Grin versions with a snug fix to the axle. I would bolt it up to one of the brake mounts. If needed to ensure no rotation if the TA pivot bolt loosens, fab/drill a custom arm link from 1/8" steel flat stock from the hardware store.

In any case, because of the freewheel the motor will apply torque in only one direction. For an aluminum frame where the dropout slot should not bear motor torque, clock the axle in the dropout and the TA on the axle fully in the direction of wheel rotation when fabbing/tightening down the TA so the TA will bear the entire motor torque (counter to wheel rotation). Just put an adjustable wrench on the axle flats to do the clocking.

HolgiB said:

- Should I design an open torque arm from 5-6 mm steel for one side ? Similar to a reinforced dropout ?

Click to expand...

You can certainly do this if you leave sufficient meat around the closed end of the slot. For an aluminum frame, I would go with a 5/16" or 3/8" mild steed TA if you are contemplating only one - primarily to minimize distortion of the axle flats.

Although clamping TAs are arguably the best choice, your modest power situation makes less aggressive solutions suitable. There are many TA examples on ES. Here's an example pretty much like what you propose.

Chalo-You pointed out to me to I referred to the wrong Model tire I'm using. It is the "Slick", which is a tire. w/ sipping.
I does seem odd that WTB would name a tire w/ a "normal" type of tread a "Slick"

motomech said:

Chalo-You pointed out to me to I referred to the wrong Model tire I'm using. It is the "Slick", which is a tire. w/ sipping.
I does seem odd that WTB would name a tire w/ a "normal" type of tread a "Slick"

Click to expand...

Ah, yes. That's a legacy tread pattern that was originally called "Slickasaurus". It's been around a lot longer than ThickSlick.

Wow, first thanks guys for all your replies.

@mototech: You are somewhat right on tires but it seems I never have that much luck with "flat-resistant" tires.
As you already spied out my rear tire is simply a cheap knobby tire I had lying around since this has happened to my
Schwalbe Marathon Tour Extreme:
View attachment 1


A fat nail went through the complete tire and caused two big holes in my tube. Hence my wish for more or less easy
repair. May be it is somewhat bad luck but I had as much flat tires with "flat-resistant" tires as I had with
cheap tires plus Zefal Anti-puncture liner which you put between the tire and the tube.

All in all I do not trust those expensive no-flat thingies. Too many nails, wire pieces and stuff punctured my tubes.

Those WTB Thick Slicks really look wicked but will not play nicely with mid-european autumn & winter which directly
translates to wet and muddy surfaces.

@neptronix: My MAC is indeed the cassette version with 12 mm axles. Sounds as if I could risk either screwing up
my dropouts or my axles if I use less than two torque arms ?

I have only seen up to 550W at the battery side shown on my LCD3 display so far on steep section in the woods but
in theory the controller maxes out at 20 amps. So this translates to roughly 800W with my 10s5p pack.

Well, seems to me I am somewhat stuck in this position and should rather keep both torque arms and may be thinking
about getting another Schwalbe or Continental tire with flat protection. If I wasn´t such an old grunt in regard to
newer stuff I could even go the tubeless route since this seems to work for a lot of folks without having flats.
Especially those with fatbikes.

@teklektik: Thanks ! :thumb:
Those DIY TA definitely look interesting. I will think about it.

A single TA is all you need so long as its on the cassette side.

Little update:
I decided to go the "better safe than sorry"-route and bought some Schwalbe tires with the highest protection level I could get.


I think they were called Marathon Plus MTB and have protection level 7. The tires were pretty cumbersome to mount because they are stiff but hopefully they will keep me from having flats somewhere in the woods. :wink:

The best tire can’t save you from an occasional flat. This all comes up to location and riding conditions. Some people are living or riding in areas that are making it impossible to prevent punctures.

Going tubeless is making for quick and easy flat repair, but it is coming with expanses and somme troubles too. Best tubeless route for bicycles is the way they are doing it in DH racing: tubeless rated tires, tubeless rated rims, Cush Core tire inserts, half a liter of slime. That is pretty expansive, and more trouble to change a tire. But, it does magic to save the day. Better ride, amazing rim and tire saver, better traction with lower PSI.., and you can complete the ride on a flat most of the time.

@MadRhino: What you say is all correct !

But I rather do not feel like turning an average MTB which is used for cross country touring with some trails at best into something close to a motorcycle. Everything you described (tubeless DH tires, cush core inserts, etc) make a regular maintenance necessary.

Most sorts of slime used for tubeless I know require both regular refill and sometimes even a complete removal followed by a clean up. A friend of mine tried tubeless with his non-motor MTB and reverted back to riding with tubes. I don't remember the details too much but the slime didn't fill up the hole in the tire he had and inserting a tube was a mess because of the rest of the slime in the tire IIRC.

I guess I rather stick to flatproof tires like the ones I bought plus spare tube and may be some repair spray in order to fix a flat without removal of the tube.