I have a 29" mountain bike I'm going to put a motor on. I'm going to replace the back wheel with a 26" and my question is about the gears. I need two of them in the same side to freewheel independently one for the motor and one for me to pedal. and I can't find anything online telling me which kind of hub I should use. Can I just use a standard single gear freewheel hub and chuck two freewheel cogs on? I don't want to buy them then be stuck waiting a month for a new hub.
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You'll mess up the geometry of your bike by changing the back to a 26" wheel. Plus the 29" probably has a disk brake and disk hub... can you fit a V brake on the back rim? Maybe if it has mounts, but unlikely mounts suit a 26" wheel. Stay with your 29" wheel and your disk brake, and investigate for a cassette that wil slip onto your freehub and do the job required.– Criggie ♦Jan 12, 2017 at 19:25
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Tell us more of the motor please - is it a hub motor or a mid drive?– Criggie ♦Jan 12, 2017 at 19:26
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You can, in theory, get a regular multi-speed freehub axle and put your own choice of sprockets on it, with spacers between. Or you could just use two cogs on a suitable cassette, if the standard sprocket tooth counts suit you. (It would be unwise to use two adjacent sprockets, though -- you need at least one space between.) But it's impractical to put a 26" wheel on a 29" bike.– Daniel R HicksJan 12, 2017 at 22:43
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Daniel - if you put two chains on a multi-speed freehub, the crankset will also move when the motor is on -- leading to the real possibility of breaking ankles...– RoboKarenJan 12, 2017 at 23:23
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I think mid motor kits usually do this at the chainring, not at the sprocket. There are freewheel chainrings available. Look up Cyclone Double Sprocket– MichielNov 4, 2019 at 18:55
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1 Answer
First, if you use a 26" wheel in back, you won't have any brakes as they won't reach (unless you have rear discs).
Second, because you mention that you want a sprocket chain on the left hand side going to the motor, I assume you're going for some kind of off-board solution. These have been really deprecated with the rise in good hub motors as well as mid-drive solutions.
Update: you clarified that you wanted both the motor and the regular chain on the right hand side. As far as I know, there aren't any freewheels that are split so that they can take two chains that freewheel separately. The best you can do in this scenario is to use a regular freewheel and put a one-way bearing on the cog that's on the motor. It'll mean the motor chain will not freewheel -- but it'll also mean the cranks will move when the motor is moving (with the real possibility of breaking your ankles). The safer way is to use a flip-flop hub or disc-brake mount to put the sprockets on the left hand side using either a left-hand freewheel or a one-way on the motor. That way, the bike's freewheel will make sure that you can't break your ankles.
tl;dr It'd be so much easier for you to get a 29" hub motor wheel -- or to keep the current wheel and go mid-drive.
Not an answer to your question about left-hand sprockets so feel free to ignore.
answered Jan 12, 2017 at 10:03
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Cheers for the tip on the brakes. I haven't had much to do with bikes since I outgrew my bmx. Jan 12, 2017 at 10:18
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I'm going to use a razor scooter motor I have laying around. I just need a way for two gears on the same side to freewheel independently so I can pedal assist or kick back and use the motor. Jan 12, 2017 at 10:20
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Yeah, that isn't going to work. I'm not aware of any cassettes or freewheels that have dual capacity. What most people do is have a one-way bearing on the motor sprocket instead (i.e., up top). Jan 12, 2017 at 10:31
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So I can get something that'll make it freewheel in the right direction? I was gonna just use a flip flop but I figured it'd just twist off on the left hand side. Jan 12, 2017 at 10:42