Mid drive on a three speed

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Scotch66   1 µW

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Mid drive on a three speed

Post by Scotch66 » Jan 21 2021 8:56am

I am considering a Bafang 1000w mid drive on a three speed bike with gears in the hub, please advise me of the good and bad of this setup. My goal is high speed throttle on roads until I get to a local bike path where I will pedal with or without assist. I live on flat terrain. Thank you.

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neptronix   100 GW

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Re: Mid drive on a three speed

Post by neptronix » Jan 21 2021 12:16pm

A hub motor would work in this instance and have higher efficiency, less reliability issues, and lower cost.

Mid drives shine on hills.. on flats, it's hard to glean any advantages from them.
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spinningmagnets   100 GW

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Re: Mid drive on a three speed

Post by spinningmagnets » Jan 21 2021 3:35pm

The most common 3-speed's are the Sturmey Archer, and the Simano Nexus. Both have a similar construction.

2nd gear is by far the strongest gear if you want to enjoy hard starts. For hill climbing, the best bang per buck is switching to a smaller chainring.

Test ride the stock chainring in your top gear on flat land, then record the speed in MPH. Calculate the percentage of top speed loss you would be satisfied with (*10% slower?) And then select a chainring that has that percentage of fewer teeth.

If you have a 40 tooth chainring, and you would be happy with 10% less top speed, then get a chainring with 4 teeth less, or 36T.

You would still have acceptable top speed on the flats, but in low gear, you would have 10% better climbing torque, plus the motor would run cooler.

I also agree that a powerful hub motor can be a good choice. Consider the Leafbike 1500W 4T in a 24 inch rim, 2.5 inch tire, and 52V.

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amberwolf   100 GW

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Re: Mid drive on a three speed

Post by amberwolf » Jan 21 2021 5:55pm

Since you would only have flat terrain, a front hubmotor would be much simpler to install, depending on the front fork you have. If you have a lot of slick terrain (mud, wet leaves, etc) then the front motor will take more care to ride with, as you'll have to ensure you have sufficient tire grip to prevent losing traction, or reduce power on slicker areas especially when not going straight ahead, so you don't have the wheel slide out from under you. ;)

It also wouldn't be hard on the IGH, sprockets, chainrings, or chain like a high-power middrive can be.

If you're planning on pedalling without assist a fair bit, I recommend a geared hub with internal clutch/freewheel rather than a direct-drive (DD) hubmotor, as it makes that a bit easier with less drag from the unpowered motor. But you can also simply use just a *tiny* bit of motor power to overcome the drag of a DD hubmotor if necessary. (with some controllers, like the Phaserunner, there's even a direct option for this in setup).

If a bit of drag (it's not much at typical pedal speeds, but it can be noticeable) isn't a big deal, then a DD hubmotor is simpler and has less to go wrong.

Either kind of hubmotor has less to go wrong than a middrive, and it also means you have effective 2WD, for redundancy if nothing else.

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