Hub motor on spring forks

Discussion in 'Electric Bicycles' started by Flapdoodle, Jun 21, 2009.

  1. Flapdoodle

    Flapdoodle Member

    One of the brushless front hub motors I looked at recommends not using it on a bike with front suspension.

    Can anyone hazard a guess as to why this would be bad? The only thing I can think of might be poor ground through the suspension.

  2. Meer123

    Meer123 Member

    this is a very common topic and with a little looking around, your question was probably addressed a dozen times over however since we're chatting bout it ... forks (especially the drop-outs) are not normally the focal point of the bicycles propulsion since most (if not all) bikes are rear wheel drive. Add to the fact that most normal/everyday cyclists only produce several hundred watts of power and those are usually delivered in bursts (however, serious bike enthusiast or pro cyclist can produce around 1500 watts) ... the short version is ... bike forks are there to hold your front wheel in place and be effective front mounted tillers/rudders and are not meant to deliver power to the ground. Steel and cro-mo and other variations/alloys are strong and unless they are the skinny weight saving racing stuff - are usually capable of addressing the torque of the "typical" 36V hub motor. Cheaper forks or certain aluminum forks geared for weight savings and less robust suspension forks are not recommended for their do not have the needed structural integrity ... also, drop-outs can strip under certain torque loads - especially true if made of aluminum or on less robust suspension forks - this is no laughing matter unless you like making your bike a unicycle while moving ? I suppose the fine line here is to determing how much power is too much to overcome a front fork (or it's drop-outs) ? I have a bike with an aluminum front fork - not a cheapo fork but still questionable (aluminum Bontranger Switchblade fork) and I too would like to mount a motorized hub (500W Crystalight made Go-Hub with 48V of power) and would love to know if anyone has any input on whether or not my aluminum fork can handle this ? This is a pretty "standard" hub - not a 72V hotrod hub or anything like that ... do you think my drop-outs can deal with it ?
  3. grouchyolfart

    grouchyolfart Member

    A problem I had with suspension and "beefy" forks is that they're not wide enough to accomodate a hub motor. I installed a 350 watt hub on my daughter's comfort bike, which had a "beefy" fork. Not a suspension fork. I had to spread the fork almost 1/2" and installed washers on the axle to get more clearance for the hub to turn. After all that work, I managed to get 1/8" clearance on both sides. If the forks were just the standard size, I'd have had no problems fitting the hub motor.

    Btw, our hub motor is not grounded to the frame, so I'd suspect that it's a matter of the inside dimensions of the fork if it's wide enough to accomodate a hub motor.
    Then again..............:ack2::grin5:...I'm not an electrical engineer. :whistling:

    Anyway, my suggestion is to get the width of the hub motor, then look for a bike that it can fit. Would save a lot of sweat and cussing and swearing. I still owe my daughter $46. A buck for each "bad" word. Yeah, she told the wife what I said and she wasn't none to happy. :laugh4:
  4. Flapdoodle

    Flapdoodle Member

    Thanks for the laugh. Glad no one was around to hear me.

    I measured the fork distance on mine before I ordered, but did not account for the clearance higher up (wider rim and tire). It fits, but very close.

    I did measure a few hundred k resistance ground to the hall wires, but later it read infinite.

    The problem of the e-motor not working when the gas Happy Time is running has been solved. It took shielding on the sparkplug wire and shielding the power wires, connecting those together, and installing a resistor plug. Now I can run both gas and electric at the same time.