Well, today I was out in the car and tested the odometer against the GPS. Over 15 miles, the odo was out by only 0.2 miles so it seems the whole 16-17% error is in the speedo head and that changing the driven gear size on the cable might help the speedo but make the odo way out. I'm told that there is not that much adjustment in the head so what do I do?
All advice and info appreciated.