The GPS is correct at a steady pace. It won't keep up to the bike on quick acceleration (there is a lag). I always drive to the Garmin, not to the speedo. My f150 reads 3 mph slower than the Garmin at 73 mph. The 10 RKC is about on.

 

I remember my 2002 SERK speedo said certified on the face. Didn't think much of it until I mounted a Zumo 550 on the bike. The bike and GPS were dead on @ all speeds. The odometer was probably within 2/10ths of a mile over a 100 mile trip. I Bought a BMW over a year ago and the bike indicates 4 mph fast at most speeds above 50 mph but the odometer is very accurate. Just saying don't assume that your miles are piling up faster because of a speedo error without checking.

 

Ultra is within 1 mph of my Garmin.

 

My Garmin and speedometer match up to 45mph. At 60mph on the Garmin the speedometer reads 3mph slower.

 

I have noticed about a 2mph difference on the glide

 

The shop guy told me he can calibrate a 2010 speedo. Not sure if my 05 can be calibrated though it does have a SEST ? Can a SEST adjust a speedo ?

 

When I use my Garmin's MPH leading a group ride, my wingman will fall back because he thinks I'm speeding. 8-)

 

Have you checked your bike clock against the world clock to see how they compare? Maybe HD makes out clocks run faster so out warranties will run out faster..lol.

 

That depends on what update time you set your GPS to. If you have a 5 second update time set on your GPS, your unit can only take a new signal from the satellites every 5 seconds. Therefore if you accelerate your bike from say 50 to 60 then let slow it back down to 50 in less than 5 seconds, your speedo will not see the acceleration. I have a race GPS on my boat and its update time is set to 1/4 of a second so it updates from the satelites every 1/4 second. If I accelerate from say 80 to 90 and back to 80 in 5 seconds, it will update every 1/4 second and read my exact speed through the entire speed change with only a 1/4 second lag time.

 

I never paid much attention to the difference below 40 mph, but at 40mph on my speedo, Garmin says 38 mph. At 65 on the speedo, Garmin says 61 mph. When the speedo is buried, the Garmin reads 112 mph.

Mine seems to be a percentage off, not a set number.

Garmin agrees with my F150 and Grand Prix speedos.

Dennis