Using motors freewheel instead of hubs

[AX3L]

Awhile ago Intend released their Rocksteady crankset which effectively moves the freewheel to the crank while the cassette rotates with the wheel. This means that you can shift gear without pedaling as long as you're rolling.

This got me thinking. Can someone explain why it'd be a bad idea to use the freewheel on the EP8 in a similar way?

 

[MBj1703]

Should work and it is working.
I changed a while ago my cassette and did a mistake, which leads to a blocked freehub. I didn't even realize it till I came back and turned the wheel by hand.

 

[AX3L]

I mean yes, it's working technically. I guess my question is if it's a bad idea? Surely the motor isn't designed to be used in this way, but apart from slightly more wear on the freewheel system I can't see any downsides. The disabling of the hub can easily be done with a zip-tie between the cassette and spokes.

Now that I think about it, my first Shimano-motor experience on a rental emtb coasted completely silent as if it had Onyx hubs (the freewheel on the EP8 sounds silent as well). I guess you get this effect if the hub freewheel has too high friction, in the same way that you on an analouge bike get rotating cranks (and thus silence) if you roll it. But of course, it might have been near failure.

 

[MBj1703]

I can't see any downside at all.

 

[Zimmerframe]

The main positives will be the advantage of being able to change gear whilst not pedalling and the removal of the rear freewheel - so a reduction in moving parts.

Possible disadvantages will depend on the rider, where and how you ride and potentially the particular bike, plus as stated the extra wear of the motor free wheel, though this is probably minimal.

The chain will be constantly in motion, so ultimately more wear on the chain, chainring, sprockets, derailleur.

An EMTB obviously has higher chain wear than a none E due to the extra force being applied for most riders. The force being applied by 100+kg's through a wheel when descending/accelerating at speed must be orders of magnitude higher !

Chain slap could be more of an issue with the chain moving whilst slapping - generally it won't be slapping as much when you're pedalling as when you're not pedalling.

Risk of the chain coming off will be higher for the same reasons so it will be important to make sure the clutch is set correctly and the guide might need adjustment.

There will be a higher chance of chain breakage and destruction of the derailleur/hanger from foreign objects entering the drive train. If you consider when you're riding up "branchy" terrain, you'll often stop pedalling momentarily to stop branches flying up and being pulled into the derailleur, locking it up and tearing it off - you won't be able to do that and whilst you're descending with branches flying everywhere, you're high speed automated derailleur destruction feed system will be active and effective !

Elevated risk of personal injury/unplanned dismounts. When descending, if you're quite an active rider and move your feet about, there's a chance you could move your heel/ankle into the chain line - which will be like a blunt chainsaw. Similarly, if your trousers or something else gets pulled into the chainring/chainguide it will stop the chain and in turn lock the rear wheel.

 

[Alexbn921]

DON'T DO IT!
It will wear the entire drivetrain out faster as it's always moving.
It will wear out the motor faster.
It will give you excessive motor overrun.
If you miss shift it will destroy your gears or brake your chain.
If you get a stick in the chain it will destroy the derailleur.

Basically if anything goes wrong with the drivetrain it will eat itself and anything around it.

 

[gbarfoot]

I asked bearing man about this and the bearings in the motor that spin in this situation are not meant to be used much.....He said that those bearings would wear and to not consider this.....would be interesting if a motor company designed the motor to do something like this

 

[Suns_PSD]

I've seen what happens when I lose a chain at speed, with a freewheel.

You could easily have complete destruction of many parts if you lost a chain with no rear freewheel.

 

[Zimmerframe]

I think the system always moving under very very minimal resistance

Yup, whilst there's a lot of potential force, there's not much resistance so the wear may not be that much substantially higher. I think the newer Shimano ep8/ep6 with di2 offer the option to spin the motor up for a revolution to enable shifting without pedalling - but that's not really spinning all the time.

One other option you could have is re-gen on a mid drive in that configuration with the rear brake controlling motor resistance/charge - though you wouldn't get much from it so probably not worth the development/faff !

 

[AX3L]

Thanks for all the really good input!

Many of them are really valid concerns, but the wear and potentials for jamming sticks and debris in the mech and cassette is a risk I'm willing to take for the benefits. As for the wear, it'd be interesting to weigh the upside of less 0-100% accelerations vs always spinning and seldom going from 0%. As for the potentials of ruining the mech my plan would be to use a very very thin and fragile ziptie (just as prescribed by Intend for their system) that would brake immediately upon problems giving you a regular freewheel in the rear again. Of course, if the stick has already jammed in there and you give full power that won't help but it's a risk I'm willing to take.

What I'm not willing to do is bricking the motor. Now the warranty just expired (one of the first EP8 delivered worldwide) which makes the potential loosing of warranty less of a concern but on the other hand making me pay for any damage and wear this might cause myself. So if someone has more input here (or any other), please feel free to add!