I would think anyone could compare their bike speedometer against the miliage markers on the freeway. Doing 60 for one mile should take exactly one minute. I've noticed a difference too. This past weekend, I took the bike up a little over the speed limit. I know what the speedometer said and when I got home I checked the history on my Zumo 660. It read about 6 MPH slower than what my speedometer had read.

 

every vehicle I have put my GPS in has been off. I have a 2004 Nissan titan and a 2004 Jeep Rubicon. They were also off in my 98 corvette and my 2005 mustang. speedos were 2-4 miles off at 60 on the speedo.

 

I upgraded my SERT to the TTS MasterTune and it allows you to calibrate the speedometer. It now reads exactly the same as my Garmin 550.

 

bunch of guys i rde with always say im riding faster than what my speedo says .. this is on my softale with an aftermkt speedo ... my speedo says 70/75 and theirs say around 80/85... i have had a few tickets too , but not when i was doing what my speedo read

 

Mine reads within 1 mph of the Garmin. I wonder if the stage 1 download has anything to do with it.?

 

My Ultra reads about 2mph slower, the truck also about 2mph slower, but the car is dead on. Like others have said though, the GPS should be very accurate.

 

mine is slightly different, i dont' think its 4 mph though. Usually within 1-2 mph at most. In my truck, its exactly the same.

 

So are you guys saying that when the speedo reads 60, I am actually going 64? Or are you saying that when my speedo reads 64, I am actually going 60?

 

Correct

 

my bike speedo is always 3 mph faster than the GPS, no matter what speed, its always 3 mph difference.

The same GPS in both my cars reads the same speed between the speedo and GPS.