I have recently installed a ZUMO 550 on my RT. One of the first things I noticed was a discrepancy between the speedometer and the speed on the ZUMO. When the ZUMO indicates 60 mph, the speedo shows about 63-65. I have noticed about the same difference in mileage. I rode 107 miles (ZUMO) a few a days ago and the speedo indicated 112 miles for the day.
So, what is accurate? Holy Cow, how many miles do I really have on my bike?