Speedo is way out.

[Footy.]

If the odometer indicates correctly, I think your supposition of the root cause being either the magnet becoming weaker over time, or the spring weakening is correct. Shortening the hair spring should help correct the percentage of error on a mechanical gauge..

Thanks for your response.

Given that people are largely reporting the speedometers are reading fast, would suggest its the spring that is getting weaker over time in these older speedo's. If it was the magnet weakening you would expect it to read slower.

I have not had a close look at my speedo. But it seems to me to be such a fine magnet/spring balance, you would expect they have to be calibrated when made? It would be nice if there was an adjustment screw for the spring tension like in mechanical watches. But I am sure the GSers would have found that by now if it existed.

[chuck hahn]

I was a friend of a cop back in Royal Oak back in the day. Don was the scooter cop and hung around bike nights so we all got to know him. we went and he radared me and we found the speedos would generally read within 2 or 3 % one way or the other. He also told me that those "your speed is" mobile stations are calibrated very very tightly if you can find one close by, just ride at a few speeds on the dial and watch what the station says.

Or if you know a cop get him to take you to an out of the place industrial park after hrs and run thru a few different speeds and have it checked against radar.

[wymple]

Or just have your wife run 60mph steady and see what you get following her. Most newer cars are spot on.

[tkent02]

You can't tell me you actually look at the speedometer while you're riding? Isn't that kind of dangerous?