Is this speed possible ???

Discussion in 'Motorized Bicycle General Discussion' started by borntofli, Aug 31, 2012.

  1. borntofli

    borntofli Member

    Joined:
    Jul 27, 2012
    Messages:
    305
    Likes Received:
    0
    I just installed a speedo on my bike and got a top speed of 41mph.......

    I have a 39 t sprocket......1/3 to 1/2 throttle reads 22-26 mph...This is the first time ive run wot to see how fast it goes, was waiting for it to explode and send me into the pavement.....

    66-80 china girl.....
     
  2. The_Aleman

    The_Aleman New Member

    Joined:
    Jul 31, 2008
    Messages:
    2,658
    Likes Received:
    1
    Sure it's possible, but bicycle speedometers tend to not be perfectly accurate, especially at higher speeds. That's almost 8500RPM, definitely pushing your engine hard!
     
  3. bairdco

    bairdco a guy who makes cool bikes

    Joined:
    Aug 18, 2009
    Messages:
    6,333
    Likes Received:
    19
    it's possible, but...

    what other mods to the engine have you done?

    what kind of bike?

    tire size?

    your weight?

    flat ground?

    wind?

    there's a lot of factors. a well built bike with a lightweight rider can get into the 40's (or faster) but if all you've done is change the sprocket, it's unlikely.

    my first bike was a stock 26" cruiser with a 36 and i got 38mph.

    my race bike is a heavily modified china engine on 20" wheels with a 36 and it tops out at 43.

    my old 26" with an insanely modified motor and a 28t blew up at 62.

    aleman witnessed it at 54. :)

    i've seen and had bikes easily go over 40, but they've all had a lot of work done to them.

    all that being said, you mighta got what i call a "lucky motor." sometimes you'll get one that goes fast right outta the box.
     
  4. Ludwig II

    Ludwig II Well-Known Member

    Joined:
    Jul 17, 2012
    Messages:
    4,703
    Likes Received:
    41
    The first thing I'd do is check against other speedos to ensure it's something like accurate. My van say 34 when it's doing 30.
     
  5. shwnrttr

    shwnrttr New Member

    Joined:
    Dec 2, 2009
    Messages:
    336
    Likes Received:
    0
    you can get those bike speedos pretty accurate if you measure the hieght of the tire(in inches) then multiply by pi(3.14) then convert the numbers to milimeters. this would be the value you enter into the speedo. that will get you pretty close to correct. but not perfect. my tire measured 2257mm. but to get a more accurate reading i had to enter 2233mm. into the speedo.
     
  6. turbo1889

    turbo1889 New Member

    Joined:
    Jun 12, 2012
    Messages:
    27
    Likes Received:
    0
    Time yourself between mile markers with a stop watch and then do the math. Gives you a nearly perfectly accurate result every time and gives you a good average over a mile long section of roadway so you know how much time you need to budget to commute how far via motorized bicycle.
     
  7. Ludwig II

    Ludwig II Well-Known Member

    Joined:
    Jul 17, 2012
    Messages:
    4,703
    Likes Received:
    41
    Isn't doing it accurately some sort of cheating? How are we supposed to hold pointless arguments if you go around getting things right?
     
  8. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

    Joined:
    Jan 8, 2008
    Messages:
    11,529
    Likes Received:
    1
    My daughters Cavalier speedometer says 65 when you are going 71....I know because I got a ticket last night going to get a bacon sundae at Bogus King.

    A 137.49 dollar sundae.
     
  9. Bikeguy Joe

    Bikeguy Joe Godfather of Motorized Bicycles

    Joined:
    Jan 8, 2008
    Messages:
    11,529
    Likes Received:
    1
    P.S., I have never wanted to waste the money on a speedometer for a bike that will not go the speed limit. ;)
     
  10. Ludwig II

    Ludwig II Well-Known Member

    Joined:
    Jul 17, 2012
    Messages:
    4,703
    Likes Received:
    41
    We're stuck with a regulation for a speedo even on a 1kw classified bike, all 16mph of it. And with built in illunimation.
     
  11. 2door

    2door Moderator
    Staff Member

    Joined:
    Sep 15, 2008
    Messages:
    16,301
    Likes Received:
    25
    Another method for accurate calibration is to make a mark on the front tire where it meets the floor and a corresponding mark on the floor. Roll the bike forward (must be a straight line) for one wheel revolution then mark the floor again where the tire mark is. Measure the distance from floor mark to floor mark and convert to metric if you don't have a metric tape. This is the number in milimeters that you enter into the calibration.

    Example: 2073 is the ball park number most speedometers suggest for a 26" wheel. Due to differences in tires that number might not be exact. Using the method I described above will be accurate for your tire diameter.

    Tom
     
  12. nightcruiser

    nightcruiser New Member

    Joined:
    Mar 25, 2011
    Messages:
    1,180
    Likes Received:
    0
    ... or you can just velcro your GPS to your gas cap and take it for a ride (running on the internal battery of coarse). I had a cheapo speedo on my bike and wasn't sure it was accurate, low and behold it was dead on when I ran with my GPS in place to check it. So cheapo speedo's can be accurate. I did nothing special with mine, just set the tire size and rode...
     
  13. mapbike

    mapbike Active Member

    Joined:
    Mar 14, 2010
    Messages:
    5,380
    Likes Received:
    1
    I also checked my bike speedometers with my GPS all three of mine were with-in 1 MPH or dead on after doing as Tom has suggested above, all of mine are wireless models I ordered from main land China for just a couple bucks each, one of them has been working like a champ since 2009, so yes, the cheapo speedo's can be accurate and reliable on the MB's in my experience.

    Peace, Map (^)
     

Share This Page