Speedometer Accuracy ?

[NSASarge]

Not owning a hi-tech GPS at the time, I had Deb pace me with her 2013 Civic Si since it has an all digital dash. We found that the speedo on my 2010 Voyager was off by about 5 MPH at 55. My speedo said 55 and the Si speedo said 50. This was with the stock tire 170/70/16. Now I have heard that MOST motorcycle speedos are off by as much as 10%! ! Thjis would seem to hold true. Now I have also heard that some of us have gone to a 180/65/16 tire (which is smaller) and that their speedo is "now correct"!?!?! This doesn't make sense to me. A few years ago (pre-Voyager) I went with the Metzeler Stage I Upgrade tire on my '05 Nomad which was a 180/70/16 and was said to correct the speedo. I loved how it changed the ride and handling over the OEM 'Stones. I just bought a Dunlop E3 in 180/70/16. Gonna have to check it again. Any thoughts?!?

[bikebrain]

As far as I'm concerned, THE answer to my 09 and 13 voyager speedo error is
SpeedoDRD from 12oClockLabs LLC (http://www.12oclocklabs.com" onclick="window.open(this.href);return false;)

They had a model K3 that's plug and play on the voyager (though if it's got KAMS, install time goes from a few minutes to maybe an hour, since you have to work around the fan box.

[krasmu]

My 90 xii with OEM size tires as compared to my gps.
Speedo @ 25 = gps says 29
Speedo @ 55 = gps says 55
Speedo @ 70 = gps says 65
Yes they are known to have issues with speed but most say that the odometer is dead on. This is what mine does. My OD is dead on with the gps and since these bikes are also known to have fuel gauge accuracy issues. Most of us use the odometer as a fuel gauge and it is more important to have accurate fuel gauge than speed. Changing tire size would change odometer also and pull it off accurate.