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Sigma Sport 800 Bicycle Speedo
By Chet Walters
purchase at any bicycle shop

After bringing several bike computers home from the bicycle shop (Thanks Ray at Franklins!) and bench testing them (electric drill in a vice to simulate a rotating wheel), I settled on the Sigma 800 designed in Germany and made in China (retail $29.95). I could make NO OTHER of these bicycle comupters work at over 75MPH so the SIGMA is the one to get if you want accuracy up in the high numbers.

The installation is similar on my Valkyrie, ZX-6R and my X so.... I chose to mount the head on the handlebars with the sensor on the rear wheel. The head removes with a clip for safe storage and the new model of Sigma can be programmed for two different bikes so if you want to you can just buy one head and then buy a second sender for your other bike.


Using 3M body molding double stick I taped a " round ceramic magnet inside the rear disc hub at the outer edge. You can use any large magnet, this one is like you'd stick on your fridge. You really need to get a larger magnet than the one supplied with the Sigma for this to be accurate at high speeds because of all the extra metal on your bike that might interfere with the reed switch sensor. Get the magnet at any craft store. A better magnet would be a "rare earth" magnet or one from a defunct computer hard drive. 

For the sensor, since the Sigma's has a nice long flat edge just the right size, I used the same tape to stick it onto the rear caliper bracket which sets it at the minimum 5mm distance from and centered on the magnet. The wire that runs from the sensor to the head unit was, of course, way too short so I simply cut it and added about four feet of 24 guage bell wire routing it along the rear brake line with small wire ties, under the seat & tank then up to the handlebars. I did this on all three bikes.

For lighting on the Valkyrie, I re-mounted the head under the bar clamp on the big nut. I use a tiny micro light from Radio Shack mounted under the bar clamp with a little plumber's putty. Easy to hook up. Ground it on the clamp and run a hot wire up to your brake lever light switch. Tie into either the wire there that's always hot so the light is always on, or like I did, hook it to the other side which is only hot when the brake lever is pulled in slightly. Whenever I need to look at the "watch" I just pull in the brake lever a little. Instant momentary switch there. Idea by MarkT of the VOA which I modified to be momentary.

Stock Chrome bar clamp shown with Valkyrie sissy bar badge 08F85-MZ0-A00 applied.

The Sigma sports a dual display with the speed in MPH or KPH always on top. The lower can be easily toggled with the large bottom button among running time (up to 10 hours), time of day, max speed, average speed, trip distance (to 999.99 accurate to 1/100 of a mile), and an odometer (to 99,999). To reset, just hold the upper button in for three seconds and trip, elapsed time, max & average speed go to zero. The Sigma can be calibrated in millimeters for the wheel circumference (others I tested were centimeters). It is stated to be accurate up to 183 MPH 0.03 but I was able to bench test it to 350 MPH without mishap. This makes it the most accurate with the highest speed of all models I tested. I'd stack it up against any distance measuring device around. No other one that I tried would work above 75 MPH.

Using a bicycle trip computer lets you use your bike's trip for a gas gauge while still keeping track of your trips easily and the Sigma gives you a clock besides. The other stuff it is capable of are icing on the cake, but fun. With the two odometers, you can start on a long trip keeping the total mileage on the big one and resetting each day to keep track of daily runs. The Sigma is "auto-start/stop" which means that the total trip time is a record of only the time that your bike is actually moving. The only drawback I found to the Sigma is that to reset the big odometer, you have to actually remove the battery then reprogram the wheel size and the time of day. Not a big drawback, but a button would have been nice. I've heard the new model in stores now, let's you reset this without a re-program.

For the general interest, measured by runnout the Valkyrie's rear wheel circumference with a fairly new Dunlop tire on it is 2018mm while the front with a fairly worn Dunlop on it is 2080mm. Since the Sigma makes you set up for MPH differently than KPH by dividing the circumferences by 1.61, enter 1253 for the rear and 1292 for the front. I found my Valkyrie speedometer to be accurate to 35 MPH but from 35 to 75 MPH it is consistently three MPH high and from 75 to 125 it is consistently 4-5 MPH high. My ZX-6R is just about the same. For every 40 miles on the stock odo, add 1 mile. Formula is MILEAGE + (MILEAGE/40) = ACTUAL MILES. On the VTX, I found that the stock speedo (which keys on the rear wheel through the output shaft of the tranny) is almost spot on if you have mounted a Metzeler 200 tire on the back. Note that the Metz tire is larger by about a half inch than the stocker. As it is, the VTX with the Metz 200 tire is only about two miles an hour too high at 80MPH.

Your mileage, of course, may vary, but only slightly unless you have a Valkyrie Interstate which has a magnetic pickup instead of the gear driven one on the Valkyrie Standard.


Here's another application on a sport bike.

Questions? Contact Chet at Chet says 'Be sure to write!'

Chet's Valkyrie Pages Rattlebars Mfg. Chet's VTX Pages