Just here for the technical aspects.

Discussion in 'Introduce Yourself' started by Nerobro, Mar 20, 2008.

  1. Nerobro

    Nerobro Member


    Obviously i'm new here. I've been pondering a superlight motorcycle, and ti seems the best way to acomplish that is to put a motor on a road bike frame.

    And so i'm here. I have several methods in mind. But off the bat I was wondering how big of a frame you need to install the 48-80cc moped style motors.

  2. Demosthenese

    Demosthenese Guest

  3. Nerobro

    Nerobro Member

    "Sizes 12.5", 15", 17", 18.5", 20", 22"" What size frame did you use?

    I had a sneaking suspicion that that might be a difficult question to get answered around here ;-) I'm a moderate bike snob coming into a world of find a cheap bike and throw a motor in it people. *grins*
  4. quay1962

    quay1962 Guest


    well let me start off by saying hello and welcome...you will find more than just tech mech stuff...the 26" is the best fit, however once you start reading all kinds of avenues will blossom...good luck on your endeavors and happy motoring!:shock: here was my first build it is no longer....http://www.motoredbikes.com/showthread.php?t=5438
  5. BoltsMissing

    BoltsMissing Active Member

    I am a moderate intelectual bike Brat on the fringe of society who stumbled into a world hard rubbish bike frames picked up from snoburbialand and grinded a motor in it, dudes and dudettes ! *smirk*
    ( we are not considered as people)

    All the Best

  6. graucho

    graucho Active Member

    Welcome to MBc! Home of many answers, and awaiting your ideas. 26" mountain bikes have been the kindest fit to me. "Cruiser style" 26" have more room for mounting. But you might have to slightly modify the front mount, in some cases its thicker. Fairly easy.

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  7. Abeagle

    Abeagle Guest

    Welcome to MBc. :cool:
    Lots of great pics and info here.
  8. mickey

    mickey Guest

    Hello Nero, and welcome. I've been pondering an ultralight dirtbike as well. I'm keen to see what you come up with.
  9. RdKryton

    RdKryton Active Member

    Welcome to MBc

  10. Nerobro

    Nerobro Member

    Thank you for the welcome.

    More 26" responses. :) Bike frames are not defined by their wheel sizes. It's a fairly common move to put 650c wheels on 700c bikes to gain fender clearance. Changing the wheel size, doesn't change the frame size. A 26" frame would be a freaking skyscraper.

    Yaknow, a mountian bike with this motor on there and a big big sprocket could be one very fun trail bike.

    If you've built one of these. Please, take a measurement from the center of your bottom bracket, to the center of your top tube.
  11. fetor56

    fetor56 Guest

    G'day man and welcome to MBc.
    My general rule of thumb is 36cm(14") measured from the INSIDE of the triangular frame from the crank to the seat.You can go slightly smaller but it's really not recommended cos there's always routine maintenance to do.You can also get a smaller sparkplug if necessary(Champion CJ7Y)
    You can also grind the engine down and have aluminium brackets welded to it but that's another story.
  12. Nerobro

    Nerobro Member

    Well, that's some useful information. Thank you. Actually, I think both of my bikes would cover that.
  13. drimpact

    drimpact Member


    The smallest frame I have used was a 16.5" Trek Navigator (03 model) It was a super tight fit.

    For my personal bike I use a 19.5" Diamond back Outlook.

    Fetor's info above is 100% correct! When I am measuring a frame for use I am looking for 14 or more inches measured from the top of the bottom bracket to the bottom of the top tube.

    Other frame geometry comes into play, but at least 14" is where I start.
  14. Nerobro

    Nerobro Member

    *grins* I'm glad you know what frame sizes are. :) Thanks, that measurement helps, a lot.
  15. Esteban

    Esteban Active Member

    I am sure many of us do know what a frame size means on a bike. Most of the answers of 26" bikes, that you received , are still correct . Many of the bikes, you will see modified with a motor , are standard cruiser type bikes sold in department stores. They are NOT sold by their frame sizes, only by their wheel sizes, like bikes were sold years ago.
  16. friedlbug

    friedlbug Member

    Wheel size is still an important component, too. I realize you asked about frame size, but you'll also be interested in wheel size when you're ready to start considering torque and speed. Also, for the money, you may find that a department store bike gives you the best value for a motorized platform when steel construction is a benefit and a few pounds one way or another doesn't matter.
  17. Nerobro

    Nerobro Member

    But 26" isn't the frame size. I'm not sure how that makes it a correct answer to me asking what size frame people installed their motor on. Even those cruiser bikes have a frame size. Weather they're sold by them or not.

    Even to that end http://sheldonbrown.com/26/index.html 26" isn't a fair answer. There's no less than five 26" tire standards.

    I intend on using this bike in fairly severe duty. I wanted to start with a good bike. I'm not a tall person, so I tend to ride small frames. (as is exemplified by my 46cm Dawes) That's why I asked the specific question I did. :)

    Wheel size matters much less than frame size. If I can't fit the motor into the frame, I could have 6" or 35" wheels and still be in the same situation. (Sitting with a bike that I can't fit the motor into) No matter what size wheel I end up with, (Which is most likely going to be 700c) I can always alter the final drive ratio to match the expected speed range. I can not make the frame bigger though.

    I've begun to ask some other questions which will address the power issue. We'll see where that gets me.
    Last edited: Mar 24, 2008
  18. Esteban

    Esteban Active Member

    I don't know if you want to be too difficult, too stubborn, or too technical about your motorbike ideas. In MY opinion, I would suggest you buy one already built.
  19. Scottm

    Scottm Guest

    This has been pretty helpful and educational for me. I am building abike for someone who is short in the leg area, and it's been difficult helping describe what kind of bike he should get. I told him to take a tape measure and measure the fames for the 14 inch also.
  20. Nerobro

    Nerobro Member

    If the technical information isn't out there. Someone needs to pry it out. It would make chosing a proper bike easy. Which it isn't at the moment.

    I asked a very clear question to start this off. If you don't know, you don't know. I can accept that. That's why I later defined what measurement I was looking for. I don't see that as being difficult, picky, or technical. Just accurate.

    Thankfully, I did get the answer I was looking for. And I appreciate it greatly. In fact, I even got a BETTER answer than I was looking for. The "bike frame" size is from the center of the BB to the top of the top tube. When really it's the space between the bottom tube, and the top tube that matters.