Sigma BC800 Bicycle Computer
Reviewed by pbx
What it is: A nice little LCD display that shows speed, trip time, average speed, top speed, distance to the hundredth of a mile, and a digital clock.
How it works: The computer is removable, sliding into a small base with two metal contacts. The base mounts on your bars. A wire pair goes down your fork leg to a small magnetic switch (attached with a zip tie or included rubber o-ring). On the brake disc carrier, or somewhere else convenient, you mount a small included magnet so that it comes within a few mm of the switch each revolution. Some improvisation is required here because the included spoke mount won’t work on motorcycles. I pulled the magnet out of its little plastic spoke mount and epoxied it to the disc carrier.
Every revolution, the magnet closes the switch. The computer knows the circumference of your front wheel (you set it), and does the math.
The trip timer, and the average speed calculation based on it, stops when you stop, which is handy though it means that the time you spend at lights or stop signs isn’t included in your trip total.
Depending on your bike, you may be surprised at the speeds you have actually been traveling. My stock speedo turned out to be 6-8% optimistic, meaning that at an indicated 70mph on the stock speedo I was actually only going 65.
I believe the Sigma is claimed accurate to, coincidentally enough, the Euro-limit of 300kph, or about 183mph. Not good for top speed runs on on your nitrous Hayabusa at the Bonneville Salt Flats, but enough for the rest of us. (Professional rider on closed course only, always wear a helmet, cycl.info will not be responsible for damages, any monkey can twist the throttle, motorcycling is a dangerous sport, the more you know the better it gets, etc.)
Installation: It took me about an hour, most of which was futzing with my bars to find a good location and make the attachment as sano as possible. On many bikes it would be a 10-minute process.
Many bikes will need longer base-to-sensor wires. You can certainly splice in more wire yourself, but I opted to buy a second base (with longer wires — they called it a “rear wheel” sensor) from my local bicycle shop. I put that one on my motorcycle and the original one on my bicycle. Since the BC800 can remember two different wheel sizes, I can pop the computer back and forth between the two.
Cost: About $20-25.
