gearing and such...

Discussion in 'General Questions' started by jaker, Jan 15, 2007.

  1. jaker

    jaker Guest

    ok to stop any confusion (or maybe to create more) heres a drawing of my project..
    i am cutting this goped below at the frame and making it's rear tire turn the bike tire.

    with the current gearing on the goped it reaches 29 mph or so but thats wrapped out and noisy this is with a 6 tooth front sprocket and a 76 tooth rear..

    ive seen dyno charts for most 2 strokes have the max power around 5000-8000 rpm and at 29mph im at almost 11000 rpm with the goped..

    so i ordered a 10 tooth front sprocket this should give me a 35% top speed increase or so.. and allow me to cruise around 25-30 without being at 10000 rpm and i should be around my max power there as well .
    i dont want to sound like a angry hornet on a bike heh.

    does this sound correct? will the high gearing adversely affect anything?

  2. gone_fishin

    gone_fishin Guest

    without doing the math, it seems to me that a jump from 6 teeth to 10 teeth may have more impact than you expect...prepare to do a little low-end pedaling to help acceleration. other than that, your reasoning sounds good to me 8)
  3. duivendyk

    duivendyk Guest

    Confusion galore.Sprockets & friction drive are strange bedfellows.Does the chain drive a larger roller?.Just what is going on?.
  4. ironwarlock

    ironwarlock Guest

    you are right about 12.3 to 1 from the motor sprocket to the goped sprocket. what size is the goped tire and what size is the bike tire? so we can get a final drive ratio.
  5. loquin

    loquin Active Member

    The bike tire size doesn't matter. The speed of the bike will be the SAME as the speed of the friction roller, no matter what material it is made of. The bike tire is essentially an 'idler' wheel - it just serves to transfer the linear speed of a point on the friction roller to the ground...

    Sure, the RPM of the bike tire will be lower, but, since the diameter is larger, the linear speed of a point on the bike tire is exactly the same as the linear speed of a point on the friction roller. And, if you think about it, (with no slippage) it CAN'T be anything else, as the friction roller is in physical contact with the tire...
  6. eljefino

    eljefino Member

    A six tooth sprocket is notoriously inefficient b/c of the gear meshing geometry1; good for you for losing it.

    Sounds like the skateboard maker was trying hard to get gear reduction without a second gearbox-- our HT motors have a ~4:1 box before another 4-5:1 sprocket reduction.

    Going to a 10t will get you some efficiency, good, but you will have to bend over like crazy to cut wind resistance at speed, she'll be lugging a bunch.
  7. ironwarlock

    ironwarlock Guest

    the back tire is not turning the same rpm as the roller unless the tire is the same size as the roller. if the back tire was suspended in the air and you had another tire after that on the ground . then that first back tire would be an idler. you would also have a change in direction. tire size is final ratio on his bike. his setup is motor gear to tire gear then tire to tire. not friction roller to goped tire then bike tire.
    Last edited by a moderator: Jun 16, 2008
  8. duivendyk

    duivendyk Guest

    Loquin is correct,the rpm of the roller,or for that matter a tire acting as such is immaterial ,what matters is the linear velocity at the outside of the tire acting as a roller, which is identical to the circumferential speed of the tire,that is the ground speed.
    It you go to a 10t sprocket,your speed at 6000 rpm will be :
    26 mph,which is in the ball park,i.e. (29*6*10):(6*11)
    (* stands for multiplication and : stands for division)
  9. duivendyk

    duivendyk Guest

    One thing I forgot to mention is that you will have to turn the whole shebang 180 degrees or you'll be going backwards!,that might be something of a challenge in terms of mounting it.