[SpudRider]

I just completed a 12-mile ride across town for groceries. I mounted my Garmin GPS receiver, and recorded the odometer setting. Then I zeroed the trip odometer on the RX3 before departing.

I don't know the accuracy of a GPS odometer. However, here are the results.

Trip distance recorded by Garmin GPS receiver: 12.1 miles
Trip distance recorded by Zongshen RX3 odometer: 12.8 miles

My Garmin GPS receiver records hundredths of a mile, while the RX3 odometer only records tenths of a mile. Therefore, I don't know how close the stock odometer was to reaching 12.9 miles. However, using the most conservative estimate of 12.80 miles, I performed the following calculations.

12.8 miles minus 12.1 miles = 0.7 miles 'optimistic' on the odometer

(0.7 miles divided by 12.1 miles) x 100 = 6 percent 'optimistic'

Using the same, Garmin GPS receiver for comparison, the stock speedometer is running over 10 percent 'optimistic.'