The Suzuki GN125 is one of the least expensive Japanese bikes ever sold in the U.S., yet it has a feature that I’ve only ever seen on expensive BMW motorcycles. Atop the instrument panel is a wide, black display that indicates, by way of back-lit numbers, which gear the transmission is in.

Why would such a low-end bike have this feature? My best guess is that this was considered a starter bike, and Suzuki thought that beginning riders might appreciate being able to see which gear they’re in.

Hopefully at some point I’ll be able to take one of these engines apart to see how they did it. My initial hunch was that it’s not unlike the printed disk in the Concours engine that turns on the neutral light — I figured there would be a disk with three, concentric contact rings printed on it. If you think in binary, that’s enough to handle five gears plus neutral, with room to spare.

A bit of internet research suggests they came to a different solution that involves at least six wires leading to the display. Could be they went with simpler contacts inside the transmission, trading for more wires to the display and its miniature light bulbs. Another Suzuki design for a gear indicator uses different resistors in the transmission — this cuts the number of wires to one, which is arguably better than using three wires for a 0-7 binary indication.

I should add that all these tricks are entirely moot on modern motorcycles with computerized controls. All it takes then is the engine’s speed (rpm) and the vehicle’s speed (or transmission output rpm, preferably) and a tiny bit of math based on the transmission’s gear ratios.

I should further add that this particular problem has held my interest over the past 15 years, during which I’ve spent many highway miles thinking about ways to add a gear indicator to whatever bike I was riding at the time. I may well create one with an Arduino board at some point, and it will be as mechanically simple as I can imagine, since electronics and software are cheaper to make than “hard parts.”

Advertisements