ECRI's GPS Speedometer Calibration collects data as you drive and analyzes it in real time.
When you open the GPS Speedo screen of the app, ECRI automatically starts collecting GPS data and vehicle speedometer data. As you drive, ECRI compares hundreds of these data-points to calculate your actual tire size with 99% confidence! We have found that after 1-2 minutes of maintaining a speed, ECRI has been calculating the new tire size to within +/- 0.15 inches! This takes all of the guesswork out of setting your tire size. No measuring, no reading sidewalls, just plug in and drive. No other method of speedometer calibration is easier or more accurate.