Bandit 1250 speedometer error

I'm not a crotch rocket speeder. So when I looked at my speedometer and it said 80mph, and when I looked at the rest of the traffic all traveling at the same pace, I knew something was wrong. No way was I going 80mph! The Bandit has a reputation for fast speedometers and there are even kits (Speedohealers) you can get to recalibrate the speedometer. They cost about $115. There have to be better solutions...

How bad was the problem? I put on my Garmin Nuvi motorcycle mount I bought on eBay for $3.29 and popped on my Nuvi. Heading down the street at an indicated 60mph on the speeodometer, my GPS showed I was going 52mph. That's a 13%+ error.

Before spending more than $100 to fix this, I thought I'd try something I've done before on other motorcycles. I'm installing a bicycle computer. They cost next to nothing now on eBay (I paid less than $8 with shipping) and they provide lots of features.

These things run off of a magnet and a sensor. Since you don't have a spoke to hook your magnet to, I just use a spot on one of the brake rotors. To compensate for the greater distance from the sensor, I use a magnet from an old pair of headphones. Any magnet will do. Just superglue it to the rotor so it passes under the sensor which is zip-tied to the fork and it will work. You can adjust the computer for a wide range of wheel diameters and you end up with an accurate speedometer, trip-distance, max speed log, all kinds of things including time and temperature. We'll give this a spin, (pardon the pun...) and see how it works before spendng more for the Speedhealer fix.