Backpedaling-how important it is for an ebike?

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jeffpetersen   10 mW

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Backpedaling-how important it is for an ebike?

Post by jeffpetersen » Oct 04 2018 3:58pm

I and my friend are working on a setup that converts a bike into ebike, but currently there is slight resistance on cassette-enough to prevent any backpedaling. So I was wondering how important backpedaling is for a pedal assist ebike?

donn   100 W

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Re: Backpedaling-how important it is for an ebike?

Post by donn » Oct 04 2018 4:13pm

I have no answers, only a couple questions:

First, does this mean the cranks also can't stay still while the wheel rotates? I assume so, since that would require the very same freewheel action that back-pedaling requires. So you'd have to pedal along with the wheels, like a fixed gear bicycle.

Second, how could it do that? I don't know anything about cassettes, but I assume they have the same internal pawl spring freewheel mechanism, and it seems to me something must be gravely boogered to make that fail.

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LockH   100 GW

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Re: Backpedaling-how important it is for an ebike?

Post by LockH » Oct 04 2018 4:22pm

Sorry. Gotta ask...

I'm aware of folks riding w/assist doing "faux pedaling"... but to pedal backwards? Explain please?
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jeffpetersen   10 mW

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Re: Backpedaling-how important it is for an ebike?

Post by jeffpetersen » Oct 04 2018 4:29pm

So imagine you touch the cassette very lightly with finger. Enough to create some amount of friction.
Now, if you try to backpedal, the top portion of the chain (between chainring and cassette) will have no tension due to the friction. I hope this explains a bit more...

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Re: Backpedaling-how important it is for an ebike?

Post by LockH » Oct 04 2018 4:37pm

"Now, if you try to backpedal"... Point being? (Sorry. again...)
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(Current ride? High speed lawn chair.)
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Joined yer local chapter of EA yet?
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Voltron   1 MW

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Re: Backpedaling-how important it is for an ebike?

Post by Voltron » Oct 04 2018 5:09pm

Usually if thats happening, the frame is very lightly touching the freewheel and needs to get spacered out a little more.

The circle marks are from a freewheel rubbing.
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AHicks   100 W

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Re: Backpedaling-how important it is for an ebike?

Post by AHicks » Oct 04 2018 6:58pm

To answer your question, there should be no more issue "back pedaling" an e-bike than any other bike. If there is an issue, you need to fix it. E.g. chain dragging somewhere, something going on with the freewheel unit, etc.

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Re: Backpedaling-how important it is for an ebike?

Post by markz » Oct 04 2018 9:28pm

Nailed it!

Should be no friction whether rubbing on frame and needs spacers (I used a washer from Home Depot) or the thingy's inside the freewheel/cassette, gosh whats the name of those thingy's that click.

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Re: Backpedaling-how important it is for an ebike?

Post by Voltron » Oct 04 2018 10:17pm

markz wrote:
Oct 04 2018 9:28pm
Nailed it!

Should be no friction whether rubbing on frame and needs spacers (I used a washer from Home Depot) or the thingy's inside the freewheel/cassette, gosh whats the name of those thingy's that click.
Pawls.

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Re: Backpedaling-how important it is for an ebike?

Post by amberwolf » Oct 20 2018 8:19pm

I'd guess he's driving (or sensing the tension of) the top of the chainline, and the device he's doing it with is causing this problem.

Since he won't say or show us, we can't help him fix it, though.

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Re: Backpedaling-how important it is for an ebike?

Post by 420b » Oct 22 2018 12:40am

Sounds like you might need to clean and regrease the freehub’s bearings. Or you can just spray wd40 on it (this works temporarily, but it’s not a good idea because it actually destroys the grease).

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Re: Backpedaling-how important it is for an ebike?

Post by Voltron » Oct 22 2018 10:39am

Just an fyi since it got brought up... theres a big difference in behavior depending on if the freewheel is rubbing the frame, and whether its internally seized up. The second one is the dangerous one, as when the freewheel is rubbing the frame, it still stops when coasting, even though you cant backpedal. When its internally seized, it tried to keep spinning with the wheel and pushing chain ahead of it when you stop pedaling, leading to some serious and possibly dangerous derailment of the chain.

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