So I went back and tried to find it and I don't know where I got 3% from...it definitely was not odometer accuracy though. The actual speedometer accuracy is determined to be +/- 5 MPH at 50 MPH. Now whether that means within 10% across all speed ranges or what, I don't know. But also leads to why you typically won't get pulled over on a US highway if going 5 over the posted speed limit.I just installed SpeedoDRD speedometer correctors on my GL1800 and on my CRF250L (each running stock tire sizes). The Goldwing needed a 6% correction factor to bring it’s speedometer to match 2 different GPS units. The CRF required 5% correction to match two different GPS receivers. (Of, course, I would never expect the different GPS units to not match each other anyway). I have no idea what speedometer accuracy requirements the US might have, but if it’s 3%, Honda and other motorcycle manufacturers have been getting away with a lot more than 3% error for a long time.
Maybe you meant odometer accuracy. I have not checked my motorcycle’s odometers for accuracy.
I have not personally witnessed a GPS receiver with good satellite signal reception displaying incorrect speed.