Bafang mid drive mod

[Raboa]

A mod on endless sphere, zip tie your rear freewheel / cassette to your wheel.

Does a mid drive really need a freewheel? - Electricbike.com Ebike Forum

I have a couple donor bikes with mag wheels, and a Nuvinci 171b CVT hub that use the dreaded threaded on freewheel format. With a Bafang mid drive do I even need a freewheel at all? There is a 1 way clutch in the cranks and another at the motor. Maybe it's time to just weld one of those useless...

electricbike.com

 

[dwvl]

This is really interesting! Perhaps a better post here Mid drive cassettte zip tie mod. - Electricbike.com Ebike Forum

 

[matthewslack]

I may be missing something here, but doesn't that mean I can't stop pedalling? Why is that a useful thing?

 

[dwvl]

Mid drive systems (apparently - I don't have one) have a "freewheel" on the chainwheel. So a freewheel on the rear wheel isn't necessary.

By locking up the wheel's freewheel, it means the chain is moving all the time the bike is moving along, even if you are not moving the pedals. This means that you can change gear (using the derailleur) even when you're not pedalling!

 

[matthewslack]

Mid drive systems (apparently - I don't have one) have a "freewheel" on the chainwheel. So a freewheel on the rear wheel isn't necessary.

By locking up the wheel's freewheel, it means the chain is moving all the time the bike is moving along, even if you are not moving the pedals. This means that you can change gear (using the derailleur) even when you're not pedalling!

Not universally they don't! None of the three I have ridden have, which are Yamaha, Bosch and Shimano. I'm not aware that TZDZ2 or BBS0X have either.

Certainly there is a clutch inside the motor gear train, but with no freewheel at the rear wheel, the pedals will always be going round when the bike is moving on all the bikes I have tried.

Perhaps this advice is for people riding without pedals on a throttle only machine.

 

[dwvl]

Not universally they don't! None of the three I have ridden have, which are Yamaha, Bosch and Shimano. I'm not aware that TZDZ2 or BBS0X have either.

The original thread does specifically say "Bafang". Thanks for your info about the others... if I do ever buy a mid drive bike, I'll probably give all those a miss then (unless the bike has an IGH)

 

[Sturmey]

Not universally they don't! None of the three I have ridden have, which are Yamaha, Bosch and Shimano. I'm not aware that TZDZ2 or BBS0X have either.

Certainly there is a clutch inside the motor gear train, but with no freewheel at the rear wheel, the pedals will always be going round when the bike is moving on all the bikes I have tried.

Perhaps this advice is for people riding without pedals on a throttle only machine.

The TSDZ2 has a sprag clutch bearing between crank and chainwheel that acts like a freewheel. . This is very easy to check. With bike turned off, pedal backways. On normal bike, chainring and chain moves backways along with cranks. On many middrives, chain and chainwheel remains stationary and will not move backways when back pedalling.
The mod is not necessary with a torque sensor, so is only of use with a cadence sensed mid drive like the Bafang and recommend only a weak cable tie for safety reasons.

 

[matthewslack]

The TSDZ2 has a sprag clutch bearing between crank and chainwheel that acts like a freewheel. . This is very easy to check. With bike turned off, pedal backways. On normal bike, chainring and chain moves backways along with cranks. On many middrives, chain and chainwheel remains stationary and will not move backways when back pedalling.
The mod is not necessary with a torque sensor, so is only of use with a cadence sensed mid drive like the Bafang and recommend only a weak cable tie for safety reasons.

I checked the Bosch I am borrowing at the moment and back pedalling whilst restraining the chain to force any freewheel between crank and chainring to freewheel definitely finds no freewheel there. It's a 2020 Performance line.

I'll check the Yamaha next time it comes visiting, and I think I would have noticed in 14,000km if my usual Shimano E5000 did that trick!

 

[Sturmey]

The sprag clutch also assists the use of a throttle, in that the motor can drive the chainring and bike forward without the pedal and cranks and legs moving.
Great for resting the legs. It makes the mid drive almost as good as a hub motor for the easy (or lazy) rider.

 

[matthewslack]

The sprag clutch also assists the use of a throttle, in that the motor can drive the chainring and bike forward without the pedal and cranks and legs moving.
Great for resting the legs. It makes the mid drive almost as good as a hub motor for the easy (or lazy) rider.

One day my TSDZ2 might make it out of its box...!

 

[matthewslack]

I checked the Bosch I am borrowing at the moment and back pedalling whilst restraining the chain to force any freewheel between crank and chainring to freewheel definitely finds no freewheel there. It's a 2020 Performance line.

I'll check the Yamaha next time it comes visiting, and I think I would have noticed in 14,000km if my usual Shimano E5000 did that trick!

I'll need to eat 1/3 of a humble pie! The Yamaha badged as a Giant came visiting, and it does indeed have a freewheel between crank and chainring.

 

[Sturmey]

I'll need to eat 1/3 of a humble pie! The Yamaha badged as a Giant came visiting, and it does indeed have a freewheel between crank and chainring.

But you are right in questioning the reason for this additional freewheel/spragclutch (which gives a total of three freewheels on some mid motor bikes). For example, one version of the 250W TSDZ2 comes with a 'coaster brake function' that does not have this additional clutch and has been reported to be more reliable and have less chainwheel play/sloppiness. It has been suggested that as many TSDZ2 owners do not bother with the throttle, the sprag clutch could be welded/locked if it failed. It has been tried and has been reported to work except that there is a slight kick on the pedals when someone suddenly stops pedaling due to delay in ramping down the motor power. The user was using stock firmware, so whether this could be prevented by custom firmware tuning has not been established.(afaik)