The Computer:

I purchased a Sigma BC800 bicycle computer at a local bicycle shop for around $35.00 (CDN$). There were several models available - some a bit cheaper ans a couple a bit more expensive. I decided that the BC800 had all of the functions and features that I needed/wanted so bought that one. It is waterproof, rugged and registers up to 300 km/h. Functions include a fulltime speed display as well as a user selectable (window) max speed, clock, ride time, odometer and average speed. Be aware that the Sigma's seem to be the only units that read up to a decent rate of speed.

Installation:

Easy! First you need to determine the circumference of your wheel in millimeters which you then enter directly into the Sigma while in setup mode. The instructions are very clear and concise. I did a roll-out of the wheel using a piece of tape on the tire as a marker, then measured the distance which one revolution had taken.

Installation of the sensor and magnet was just a little bit more involved. Before installing the magnet you must determine where you want to put the sensor (pickup). The distance between it and the magnet is critical - too far and it will not "sense" the magnet as it passes it. The exact distance is in the Sigma instruction manual but with a neodymium magnet you have a bit more leeway since it has a higher magnetic flux. I used the speedo cable as a mount and merely zip-tied the sensor onto it, in a position where it was close to the magnet (see below). I used 3 heavy zip ties and the sensor seems pretty solid. It's probably a good idea check it once in a while - I do.

After much deliberation, I decided to throw out the magnet that came with the computer and bought a small 3/8" neodymium (high output) magnet for about $1.00. These are used in microphones (etc.) and are available in electronics stores, though I bought mine at a woodworking specialty store (!). I decided to mount the magnet on the rotor carrier as I wanted it as close to the wheel-center as possible to minimize centrifugal-induced mass (to negate having to rebalance the wheel). I merely epoxied the magnet to the non-magnetic (aluminium?) rotor carrier using 5-minute epoxy. I've had it on for 7,000km and it has yet to fall off - and if it does, then no big deal, I'll merely get another one and do it again.

I had to extend the wire running to the Sigma since, as it was designed for a bicycle, it was too short. No big deal. It is regular dual-conductor wire so it is easy to splice (it is not coaxial cable). I wrapped the Sigma-cable around the speedo cable and led it up and around to the back of the instrument panel. I used double-sided tape to attach the BC800 to a small aluminium bracket which I made out of a scrap piece of aluminium. The bracket was attached to the dash using one of the allen bolts which hold the dash together. Depending on your bike you might be able to use the supplied handlebar mount or...? Be creative!

The Sigma seems to be very accurate and works just as I had hoped. No regrets. Email me if you have questions.