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Thread: Help with motor selection for lightweight motorcycle

  1. #1
    Junior Member
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    Mar 2020
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    Help with motor selection for lightweight motorcycle

    Hey folks, I’m pretty new to the electric vehicle game. Plenty of mechanical experience but would appreciate some input on motor choice for my little project bike.
    I’ve been researching and it seams a hub motor is easiest but the whole unsprung weight/rotational mass thing doesn’t sound great.
    Ideally I’m looking for a top speed of 80-100kmph but low speed control and acceleration are key.

    Any help much appreciated.


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  2. #2
    Senior Member
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    May 2013
    Kildare, Ireland
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    Unsprung mass is unlikely to affect the handling of a machine like that all that adversely - I wouldn't be too concerned.
    Take a look at this thread for some relevant commentary.

  3. #3
    Senior Member Stevo's Avatar
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    Nov 2014
    Behind the Redwood Curtain- REDWOOD ORIGINAL!!
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    I agree with Spoonman … for this conversion a hub motor makes perfect sense.
    Current rides: '96 Honda Ohlins VFR, '03 Cannondale C440R, '03 Cannondale Cannibal, '06 Yamaha 450 Wolverine 4x4
    Current builds: eVOR.v3.3

  4. #4
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    Mar 2020
    Bundaberg , Australia
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    100kph on a postie bike is going to be a bit iffy handling wise. Single spine frame, very flexi forks, and insanely flexy pressed sheet swingarm with a tint swingarm axle and wheel axle , is going to be problematic. I would limit it to a true town commuter speed of 70 maybe 80kph ( if you improve the suspension). If I remember correctly ( and I may not), the swing arm from early cb/sl/cl 100/125's may be a straight fit or require just some spacers. At least they are tubular steel and the axle plate is possible to use for a bigger axle.
    Having said that the single spine frame will almost certainly limit you to a hub motor because of room. That will make the suspension have to do even more work. Not a problem at low city speeds but not a good idea for a supercommuter( highway capable 100kph).
    Add to that the very tiny and marginal drum brakes of the postie bike and you may need a better host bike if you need the higher speeds.
    As much as I love this bike ( and I do) in it's original guise, my take is is possibly not the best choice for your target use.
    One of the bikes I am considering is the late model CBr125R, though I would be aiming at a centre mounted motor.


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