And no I am not talking about a speedo you wear ... you do not wanna see this in a speedo.

Every bike I've ever owned the speedometer has read low ... about 8% (even non Harleys) ... I usually go by the GPS MPH ... On the infotainment system the speedo and the gps mph are dead on ...

So here's the question .... Does anyone know if Harley just cheated and took the input from the speedo and put it into the infotainment system? Or ... does the GPS actually calculate mph via satellites and the Speedo is accurate? Or .. I guess another option would be that both the speedo and gps are off ... say 8% low. Wouldn't it be really nice if Harley in their Rushmore "listening" actually "heard" to make the speedo accurate?

I'd love to replace the mph field on my GPS with something else ... only an option if the mph on the speedo is accurate.

 

Actually, if you drive real fast, the rear tire gets larger and self corrects I think? That is what they do on the TV. However, RIP is in the way for me to look and if I do, she snatches my ear around. Want to see my speedo or RIP in her new thong?

 

don't know about all that you said But, here is what I found out, my spedo is slower on a worn tire & when tire is replace it matches my gps, you wouldn't think it But, notice next time you get new tires.

 

Makes sense. When the tire is worn, you have about 1/4 inch less tread on the tire. A quarter inch times 2 means that the diameter of your tire is about 1/2 inch less than a new one, so, yes the number of revolutions the tire makes per mile per hour would be different on a new one versus an old one.

 

Given the same time span of travel the worn tire would travel less distance.

Using the example of a 1/4" of wear, the resulting differential from worn to new would be 1.43% hardly noticeable, especially when the allowable deviation for the speedo is 2%.

Using the above at 60 MPH on a new tire the resulting speed would be 59.14 MPH as you can see kinda splitting hairs, yes you are traveling slower but I don't think you would see that little bit of difference from the speedo to the GPS.

 

Take a Garmin with you on a ride and you will know for sure.

 

T'was my thought too ... Just thought someone would know where the infotainment system mph gets it's input.

 

I have a Tom Tom Ease mounted it showed about 2 mph differents between GPS & speedometer. in my post I said GPS. if I remember right it's the same on my car.

 

Is a GPS only correct for mph in a straight line with level road?

 

I don't think it matter, straight, curves or circles.