Power requirements in watts vs. speed & wheel rpm

Discussion in 'General Questions' started by BillMckraken, Jun 14, 2011.

  1. BillMckraken

    BillMckraken New Member

    I've done some figuring on power requirements and wheel speeds for these bikes. I believe quite a few on here have already done some of these figures, but I thought it may be helpful to list these for everyone. For me, still deciding on what to get, it was nice to get a "feel" for the power necessary as well as its' exponential nature.

    Okay so these are all figured on a standard MTB frame 26" with no fancy handlebars (lol). Total weight used was 260lbs (190lbs rider / 70lbs bike). I believe this is a decent "rough" weight to go with, of course if total load was higher; power would go up as well. The efficiency of the drivetrain was figured at 85%, I believe this is conservative and only includes drive system not motor/ engine efficiency (e.g. shown watts = req'd Engine SHAFT power). Elevation was figured at 650ft.

    Two additional key notes:
    This is the power required to maintain X speed, not acceleration or coasting power.
    Power was also figured using either 5mph head wind (low speed) or a 1% incline (higher speed). A rough average of those two powers is whats shown. The reason is that in "real world" conditions you will always have some kind of wind / grade attempting to reach these max speeds.

    1Hp = appx. 745w

    Speed - Power - RPM
    10mph - 150w - 129rpm
    12mph - 200w - 155rpm
    15mph - 250w - 194rpm
    20mph - 470w - 259rpm
    25mph - 750w - 323rpm
    28mph - 950w - 362rpm
    30mph -1100w- 388rpm
    32mph -1300w- 414rpm
    34mph -1500w- 440rpm
    36mph -1725w- 466rpm
    38mph -1950w- 491rpm
    40mph -2250w- 517rpm
    45mph -3100w- 582rpm
    50mph -4000w- 647rpm
    52mph -5000w- 685rpm

    figured I'd show the magic 50mph mark, heh. The power requirements above mid 30s gets to be fairly high. From these figures I did compare those to, what I could find for, actual speeds.

    200w electric stand up scooter @12mph
    300w electric stand up scooter @18mph

    Stock 2-stroke HT China 66cc @ appx 34-36mph
    (I believe this is average top speed on these?)
    Interesting to note then, stock engine outputs 1.5-1.7Kw; not rated 2Kw.

    Fully modded HT china 66cc or gp460 etc. @45mph
    (I believe this is about the max anyone has officially gone?)
    So here it would seem people have squeezed just over 4hp out of these, nice!

    So then to hit the magic mark of 50mph requires a minimum of 6hp. Don't think that's easily possible in the 50cc bracket.

    Hope this will help some of the builders out there!

  2. sparky

    sparky Active Member

    Was gonna remind you about the GP460, but then saw you did mention it already. Oh well...


    I'm thinking that the GP460 is just the Chung Yang version with a "Go-Ped" re-brand??

    With a larger drive sprocket and better exhaust, my friend was able to push his Go-Ped Riot to AT LEAST 45, likely closer to 50... with only 9" or 10" wheels. That engine didn't last long, but he did it!.

    I'd love to have that motor on a bicycle, but I'd probly kill myself.