Something has been playing up in my mind recently. I used to own a car which over read the speed, when it was showing 120kmh on speedometer, the gps shows its actually 115kmh. My current car now is spot on with gps reading. So my question is which will give a lesser odometer reading than actual km / miles traveled. 1. Over Reporting speedo (speedo 120kmh actual speed 115kmh) 2. Under Reporting speedo (speedo 115kmh actual speed 120kmh) I would think its 2 ?