Is the speed that is displayed on the navigation screen pulled from the bikes speedometer or is it calculated by the GPS?

 

I believe it's by GPS.

 

On just about ALL built in navigation systems, the speed listed is from the speedometer.

If you notice, the two will always display the same.

 

For sure speedometer. If the NAV speed were by GPS, Harley would have many bikes going in for warranty repair to calibrate the speedometer because almost always, they're 3-7% fast.

 

I can't believe its from the speedometer, there is always a 2-4 mph difference between mine.

 

Yes, from the speedo. I mounted another GPS to get the speed and then corrected the speedo with my Power Vision tuner.

 

Read this http://gpssystems.net/accurate-gpsbased-speedometer/

 

The BOOM! GPS readout is tied to the speedo sensor, not the speed calculated by the GPS unit. When I calibrated my buddies 2014 FLHX speedo, it corrected the GPS readout as well.

My 2015 FLHTK is dead-nuts on and completely stock, depending on what year yours is. First Harley I've owned that came with an accurate speedo.

 

Yes they are sporadic as far as accuracy. My '14 was 8% off and I set it straight with the FP3.

 

I know in most cases the GPS will calculate the speed like with my Garmin I used to have in my car. It was a portable unit that had no connection to the vehicle except for power and it would display my speed.

But...

I believe what '14 Limited said earlier about Harley tying it to the speedo because if they didn't they'd get inundated with everybody bringing their bikes in because of differences in speed between the bike and the GPS.