K bike speedometers usually run
about 10% fast from the factory. However, it is fairly easy
to recalibrate one yourself.
Many soldering irons emit a
magnetic field at a frequency of 60 Hz. (In the US.) This is
the frequency of normal household 120V alternating current.
If the magnetic field put out by your soldering iron is
strong enough (some are, some aren't) then you can use that
field to put a 60 Hz signal through the speedometer sensor
from your K bike's final drive is on order to calibrate the
Determine V1: Remove the
speedometer sensor from your final drive, turn the ignition
switch to the on position, plug your soldering iron in and
hold it close to the speedometer sensor. Your
speedometer needle should now read somewhere in the middle
to high 40s MPH. Record or remember that speedometer reading.
That speed is V1.
Determine V2: Re-install
the speedometer sensor and go far a ride with a GPS.
Ride your bike so that the speedometer reading is a constant
V1. Look at the speed on your GPS.
That speed is V2, what a calibrated
speedometer should read when the speedometer sensor is
putting out 60 Hz.
instrument cluster: Remove the four 5mm Allen
bolts on the back of the instrument cluster that hold the
instrument cluster in it's bracket. Then, depending on the
model year of your K bike, there is either a Phillips screw
or 3mm Allen bolt that holds the wiring harness connector to
the back of the cluster.
Remove instrument cluster back
plate: Place the instrument cluster face down on
a towel or something to prevent scratching it. Depending
upon the year, there are either 7 or 9 Phillips screws
around the perimeter securing the back plate.
Remove instrument cluster
internals: There are six screws that hold the
internals in the instrument cluster - four at the middle
bottom and one on each side. Remove those six screws, turn
the cluster over and carefully shake the internals out -
pull out the trip odometer knob as far as it lets you while
doing this - there's a notch in the side of the speedometer
face plate which lets it by the trip odometer rod.
Warning: Be very careful
with the instruments once removed. Try not to get
fingerprints on the face plates and be very careful with the
speedo and tach needles - they will fall off if you look at
Loosen the speedometer from the
assembly: There is a very small black screw in
the white plastic in the lower outer corner. That will
loosen the speedometer subassembly from the rest enough for
you to gain access to the potentiometer which controls the
Locate calibration potentiometer: The
arrow below shows the potentiometer that controls
the potentiometer: Use a small screwdriver or
knife tip to turn the potentiometer counterclockwise
about 45 degrees which will get the calibration pretty
Test and adjust calibration: Remove the
speedometer sensor from the final drive again. Hook the
instrument cluster back up to the bike, turn the bike on and
place the soldering iron near the speedometer sensor again.
The speedometer should now read close to what you found was
your true speed(V2) at 60 Hz. Perform
minor adjustments to the potentiometer as necessary until
you are satisfied that the speedometer is properly
recalibrated to read V2 at 60 Hz..
when testing, you misalign the connector pins on the
instrument cluster when hooking it up you can fry your $75
Bulb Monitor Unit in the relay box.
Reassemble: Reassembly is simply the reverse of
disassembly. Be sure to remember to pull the trip odometer
out while sliding the internals back into the housing.
Alternate Calibration Methods
There is a Windows PC program,
Karamba, which generates an audio output signal that can
be used to calibrate K bike speedometers.
Click here to download Karamba.zip.
Instructions for it can be found
at this link.
Here's an English translation of
what appears on the screen:
I have used this before and found that some laptops and
netbooks, in order to conserve battery power, do not put out
a strong enough audio signal and the result is that the
speedometer reading when using Karamba will be too low.
Sine Wave Generator Software:
I use the sine wave tone
generator of the freeware Audacity and the following table
that I put together for the various rear tire sizes:
And, since I like to do this on
the workbench, I built this wiring setup to simplify things:
© 2013 Drake Smith - Please do
not use or reproduce this elsewhere. Feel free to link
to it though.