Blur speedometer check with GPS

[ScooterN2]

I mounted my Garmin handheld to the mirror stalk using an Garmin bicyle adapter. I have been trying to check accuracy of the speedo.

Although its not as easy as it seems to maintain constant speed, watch the GPS, speedometer, and road at the same time. I'm sure there is some error in my measurements and a little rounding of numbers but here are my measurements

Speedo 30 GPS 27
Speedo 35 GPS 31
Speedo 40 GPS 36
Speedo 55 GPS 48

So about a 10% error.

[illnoise]

So about a 10% error.

Which is exactly what's allowable by law (from what I understand) and how most motorcycle manufacturers seem to purposefully set their otherwise ridiculously-accurate speedometers.

Nice work. But now test the ODOMETER vs a GPS on an open straight road with a clear signal. that's the REAL mystery! : )

Thanks!
Bryan

[BlueMark]

Comparing my speedo to my Garmin etrex i'm running about 12% optimistic.

Only thing is I don't believe the etrex.

When I'm going an indicated 50mph on a 50mph road I'm keeping up with almost all the traffic, if not leaving some behind. I know my fellow citizens, no way they are driving 44mph in a 50 zone - unless car speedo's run as optimistic as scooters.

At some point I'll have to take the Garmin on a calibration run in the car.

My odometer indicates about 11.5 bdu's on a route that I know is 7 miles by map - that means my bdu's are very close to standard kilometers. Perhaps after the Garmin calibration run I can see just how close.

-Mark