rear gear questions on 80cc

Discussion in 'Performance Mods' started by Rconce01, Sep 22, 2008.

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  1. Rconce01

    Rconce01 Guest

    guys a couple months back i built my first mototrized bike it was an 80cc china motor kit i got on ebay with the 40 tooth rear sproket, i noticed the bike would max out at 28 mph. So given i have a bit of a mechanical background and extensive cad training. I designed a new gear for the back that was 34 teeth. I got to 38 mph top speed with that mod alone but the engine still feels like it has plenty of power to pull an even smaller gear. Yesterday i was given a bike another 80cc usa motor but it was ported and the head was shaved. This thing once i got it runnning has some crazy power but its got a huge gear in the back 50 tooth. The funny thing is that is runs more top spped than the stock one which i modified the gear on. I was going to design a new gear for this one and i needed some advice on more or less at what point the engine will not be able to pull the gear. I am in florida so its flat and i weigh about 140 lbs.

    Also the first bike we built has now over 1000 miles and runs awesome do you guys recomend i change out anything or check on the crank or the bearings?

    I really love these bikes and i would hate for any of them to get damaged due to lack of maintenace.

    Best ,

  2. s_beaudry

    s_beaudry Member

    Yikes... 38 miles per hour is kind of pushing, if not past the safe speed limit for two wheels of a bicycle!

    I can see you like speed....
  3. Hi Ralph,

    FWIW - I have sold a number of 27T sprockets to people in FL (yes running 26" wheels)....Flat AND sea level....Can't really ask for too much more in terms of ideal conditions for speed (well OK cool weather...but it is coming)....

    Ride safe!

  4. h0tr0d

    h0tr0d Member

    27T is going to be rough in stop and go traffic. I would only use it for long stretches of highway that don't have lights or major intersections. Maybe I'm just lazy.

    Well I am lazy.
  5. Rconce01

    Rconce01 Guest

    do these litttle engines pull any gear or are they not able to pull anything under lets say 25T??

    Yes i like speed i drive a vette when i dont drive my bike :)

    I am a safe driver though. I dont drive it in rush hour so no stop and go driving for me.

    Anything i could / should do to the engine? to these neddle bearings / crank hold up or is there any upgrade.

  6. Hi Ralph,

    Can't say for sure how small one can go with the rear sprocket BUT we can make them down to 18T if you want to find out (NOTE: we can make sprockets down to 26T or 27T that will use the standard 9 hole HD mounts or for Top Hat use BUT if you go smaller you will have to rely on direct disc hub mounting of the sprocket (which is standard on out triple mount system) because at 26T or below the chain will start to ride the bolt heads on the 9 hole mounts)....

    As far as engine mods, our tuned pipe will be available as soon as we redo some header pipes....Other mods may include upgraded spark plug / plug wires, upgraded carb, port matching intake etc....

    Hope this helps you...

    Good luck in your quest for speed...but please be careful and safe!

  7. Rconce01

    Rconce01 Guest

    Great thanks for the feedback!