Mid Drives Working With Coaster Brakes

engblom

1 mW
Joined
Apr 20, 2021
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13
I have a bike with Shimano Nexus 7 and coaster brake (pedal brake). I wish to convert it to electric, but with my limited knowledge it is difficult to pick a suitable mid drive. From what I have understood Bafang does not support coaster brake with any of their mid drives. I have seen some claiming that TSDZ2 would support coaster brakes, but there are plenty of threads on various forums and blogs about it overheating. I would sometimes, especially if it warmer and I risk getting sweaty when getting to work, want to just drive by throttle and then pedal on the way home.

What options do I have?

This is the bike I would want to convert:
27-2077_xl_1.jpg
 
Get a new bicycle with disc or V-brakes. The front brake takes most the braking action anyways so you could go ahead with your current bicycle. You could weld or braze on some v-brake studs or disc mount for the rear.

The BBSHD would be the #1 choice, and the #2 choice would be the Cyclone.
 
markz said:
Get a new bicycle with disc or V-brakes. The front brake takes most the braking action anyways so you could go ahead with your current bicycle. You could weld or braze on some v-brake studs or disc mount for the rear.

The BBSHD would be the #1 choice, and the #2 choice would be the Cyclone.

The frame is aluminum, so it is not very easy to weld (at least not for an amateur like me) and sadly, my funds are not enough for getting a new bike without some heavy sacrifices and even if I would squeeze out some extra funds I rather put that into a higher quality motor than into a new bike.
 
You should be able to attach a caliper rear brake (obviously with a new wheel) and have your choice of mid-drives. I've had excellent service from BBS02's.
 
I don't believe any mid drive will be compatible with a coaster brake. Given they all have clutches (as far as I'm aware), you don't get any chain movement when you pedal backwards so it would not be possible to activate them.

Hard to tell from the pic, but it looks like that bike might already have posts for a rear v brake.

I don't really have a motor recommendation, but I'd say the BBSHD or cylone are probably overkill.
 
I wonder if someone has made some studs that could be clamped to the frame without welding... and maybe reinforced by putting a tiny bit of epoxy. That would be a good solution.
 
It is most likely a built in bicycle lock thats seen in the picture.
Get a new hub wheel with a normal hub if the coaster brake hub doesn't work. The rear dropout width is smaller then normal, also measure your bottom bracket.


Yes its available, not sure how good they are but remember your front brake takes most of the braking power anyways and its not like your going down trails on that bike anyways.

engblom said:
I wonder if someone has made some studs that could be clamped to the frame without welding... and maybe reinforced by putting a tiny bit of epoxy. That would be a good solution.
 
The TSDZ2 does a Coaster brake version with throttle, ideal conversion.

The over heating is a few posters blowing hot air onto motors not designed for 600+ Watts and then wondering why they over heat. Keep it under 500W's and they are pretty reliable, and thats way above your city speed limits.
 
When searching for a way to attach v brakes I found this: https://porkchopbmx.com/evolution-v-brake-bicycle-aluminum-mounts-clamps-adapters-pair-red/
Sadly, they do not ship internationally, so those are not possible to buy for me. Does anyone know about a similar product you can buy in Europe?
 
Waynemarlow said:
The TSDZ2 does a Coaster brake version with throttle, ideal conversion.

The over heating is a few posters blowing hot air onto motors not designed for 600+ Watts and then wondering why they over heat. Keep it under 500W's and they are pretty reliable, and thats way above your city speed limits.

In my case it would be zero city biking, but about 9 km country road biking until I reach my work place. I want to keep the speed up despite the wind almost always blows strongly against me. The wind usually makes it like it would be a long uphill trip. I have seen people saying that already around 300W they get too hot. I would at any moment prefer a TSDZ2 over Bafang if it was not for this over heating problem.
 
Its not a problem at all at 300W's. We run 400- 500 W's climbing hard with the standard engine without a problem.

I'm fairly sure that on skinny tyres, on a bike with a steep city head angle, high COG and no brakes to talk of, that anything above 25kph would be an accident waiting to happen. :D
 
Another option is a IGH with a cable actuated drum brake (for the record: a coaster brake is a very small drum brake). No special brackets required. I actually prefer them to V-brakes or disk brakes but I am a bit eccentric (aka weird).

Sturmey Archer 3 Speed 70mm Drum Brake Rear Hub
https://www.sturmey-archer.com/en/products/detail/rx-rd3
 
engblom said:
The frame is aluminum, so it is not very easy to weld (at least not for an amateur like me) and sadly, my funds are not enough for getting a new bike without some heavy sacrifices and even if I would squeeze out some extra funds I rather put that into a higher quality motor than into a new bike.
The picture you've posted shows it already has v-brakes on the front wheel, so it doesn't really matter if you have or use the coaster brake. If you post a link to the exact bike you are going to buy (or already bought) then we can verify that in it's specifications.

AFAIK the only thing that makes a CB hub incompatible with a middrive is if you want to *use* the coaster brake, because the drive will keep pushing forward and the freewheel between the pedals and the wheel will prevent the CB from being operated.

If for some reason you simply must replace the CB:

The coaster brake hub is probably 100 or 110mm, and could be replaced by a 3-speed IGH, with cable-brake. To verify the width, you would need to check the bike's specs on the manufacturer / sale page, or take the rear wheel out and measure the space between the dropouts.

If the spoke flange holes in the CB hub are at the same distance from the center as those in the IGH, and the spoke flanges are the same distance apart, then you can even reuse the same spokes to lace the IGH into the original wheel (but a bike shop that can build the wheel for you can make new spokes cheaply enough, usually a dollar each or less).

Or if you are willing to disassemble the CB hub, you could remove the brake shoes and reassemble it, so that it won't brake when pedalling backwards, if that is a requirement for your middrive.


27-2077_xl_1.jpg
 
amberwolf said:
The picture you've posted shows it already has v-brakes on the front wheel, so it doesn't really matter if you have or use the coaster brake. If you post a link to the exact bike you are going to buy (or already bought) then we can verify that in it's specifications.

I have already been owning the bike for almost a year. It got a V-brake on the front wheel and coaster brake on the back wheel. It got no studs for attaching a V brake on the back wheel. I would not want a solution where I have no brake on the back wheel as it is pretty dangerous to do a strong braking with the front wheel while it is safe on the back wheel.

Thus if I do not go the TSDZ2 route (there seems to be a version of TSDZ2 supporting back pedaling) I need to do some kind of modification to this bike. In that case I would prefer to use some kind of clamp on studs for a V brake, as it is a modification that most likely is far more affordable than changing the hub.
 
engblom said:
markz said:
22222.png

Where did you find those?

http://www.ison-distribution.com/english/product.php?part=FKITRBA

But, remember bicycle tubes come in all different shapes and sizes.

https://www.mtbr.com/threads/clamp-on-cantilever-brake-bosses.317679/
 
markz said:
engblom said:
markz said:
22222.png

Where did you find those?

http://www.ison-distribution.com/english/product.php?part=FKITRBA

But, remember bicycle tubes come in all different shapes and sizes.

https://www.mtbr.com/threads/clamp-on-cantilever-brake-bosses.317679/

Thanks, I will have to measure my bike and see if they fit.
 
Today I measured the seat stays on my bike. They are between 19.2-19.4mm. Do you know where I could find some fitting mount adapters for V brakes as it is missing the studs? If they are slightly too big I can (besides clamping them as tight as possible with the screws) add a bit of epoxy.
 
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