I took a multi state trip recently with a garmin nuvi 200 i think stuck on my fuel door. The gps showed around 4 to 5 mph slower than my speedometer. Seems like it varied the amount of mph depending on the speed but was always slower. came home and rode with some buddys on a ride and their speedo pretty much matched mine. one rode a yamaha vstar. now this same gps shows true with my trucks mph. wonder whats goin on? The bike is a 09 electraglide standard. stock

 

I'm betting that the GPS is the more accurate of the two ways of measuring speed.

 

Mine does the same thing, but only about 2 mph differents. The GPS is spot on with the radar speed checkers the hiway department sets up on the side of the roads.

 

I'm currently using a NUVI 255WT. Any GPS I've ever had always read slower mph than the vehicle's speedometer. I was always under the impression that vehicle manufacturer's purposely set them a few mph higher. I've NEVER had a GPS read the same as a spedo. Always a few mph slower.

I trust the GPS mph more than any vehicle's speedometer.

 

My 06 SG was about 3MPH faster at 60MPH and my 12 limited is about 2MPH faster than my GPS

 

Nothings going on! You are seeing the difference between the vehicle's speedo and external satellite measurement of your speed.

If you were to compare your actual speed with a brand new tyre then with the same tyre almost worn out there will be a difference, as there will be with a different brand of tyre. So a speedo reading can never be very accurate.

In addition speedos themselves are not very accurate by design. Manufacturers are only required to make them accurate to something like zero to +5%.

In other words everything is fine!

 

This has been my experience also

 

If i am travelling i use my Nuvi 760 as a Speedometer...mine is off by about 4 MPH....the faster i go, the more i seem to care....

 

In our group we had 3 GPS and all showed exact speed by setting the cruise all 3 bikes were allover some where 3 to 5 miles higher then GPS going 75 MPH makes you wonder about the bikes. Me and wife have 07 and 08 UCs when cruising 75 on my bike she is pretty close to going 80 MPH.

 

My Zumo used to read about 3-4 mph different..........then I adjusted the speedo with the TTS and now they both read identical.