Tachometer (RPM) gauge using Bike Speedometer!

Discussion in 'General Questions' started by ZnsaneRyder, Dec 28, 2008.

  1. ZnsaneRyder

    ZnsaneRyder Member

    It would be nice to actually know what RPM's your engine is spinning to prevent overrevving it, or know if your belt, or friction drive is slipping, or to set your idle speed.

    This was brought to my attention on a DIY go karting forum:


    It says by entering the correct number into the bike computer, that it makes a good and simple tach. For Example, 2850RPM would read 28.5Mph.

    *The only issue I see, is that they mount a magnet to a high speed shaft, which IMO is a bit risky if the magnet flys off, or it could cause some weight imbalance on a smaller High-RPM engine like a HappyTime.

    Well, I'm planning on doing this, but use the white or yellow ignition wire to control a transistor to open and close the connection for the bike speedometer. I figure that the pulses on that wire would be a good indicator of RPM and would eliminate the magnet.

    So, what do you folks here say about that? My goal is to make life easier for us bikers, and hopefully make our engines last longer, and a tach would do just that.

  2. SirJakesus

    SirJakesus Guest

    Nice trick. I have an old cheapie 5 function laying around somewhere... I think I'll put it to work someday.
  3. ZnsaneRyder

    ZnsaneRyder Member

    I was informed that you can also put the mag sensor under the engine shroud cover, next to the flywheel, and the magnet already in the flywheel triggers the sensor.
  4. SirJakesus

    SirJakesus Guest

    That makes a good idea even better!
  5. graucho

    graucho Active Member

    All of these good experiments are coming when I have my bikes put to sleep for the winter.
    Dang... I bookmarked yet another. Thanks
  6. hill climber

    hill climber Member

    has nayone tried the "tiny-tach". there about $40 and use just 1 pickup wire that simpley winds around the spark plug cable and is battery operated. advertised 5 years battery life and is also a hour meter. my buddy has one on a jet ski, visited there site and they have one for single cylinder 2 strokes.
  7. SirJakesus

    SirJakesus Guest

    Lots of MBC members have used this product and it's been rated highly.
    It does have the weakness of having a non-replaceable battery though and many cyclecomputers are less than $15.