Has any one noticed that there is an approximate 4 mile per hour difference between the Harley speedo and the Garmin GPS units? We did a 500 mile run and two of us checked the speedos. Both of us were 4 miles on the low side with the Harley speedo. Has anyone else noticed this?

 

Same here on both my bikes....

 

Noticed the same, now which is right?

 

Yep, and it's not just the garmin. I tired the tom tom as well once from work and the bike was still off.

 

Garmin is right. This seems to be an "issue" with most vehicles. I had a German explain to me that BMW does it on purpose - believe it or not, because they are required to by law. I guess the cops want there to be no doubt that the vehicles original equipment cannot understate the speed the vehicle is traveling. Given the variety of tires out there there's bound to be some difference and certainly as the tires wear down the speed difference gets worse yet.

 

The Harley & the BMW run 4 mph slower then the garmin.

 

of course there's another issue as far as this is concerned - when a vehicles has a warranty with a mileage limit . . .

 

Garmin is right.

 

As the others stated the GPS's are correct. Every bike that I have owned has been off. It's more like a percentage than a set number. The slower you go the less the error and the faster you go the more it's off. I believe the manufacturers want to error on the safe side and also allow for differences in tires size, inflation and tire wear.

The GPS calculates true time/distance so it is the correct number.

 

Another mystery solved. My Garmin has always read an avg of 4 faster than my BMW and the H-Ds, so I never was sure which was actually correct.