Remember the accuracy of your 2 mile (2 kilometer) distance will directly affect the accuracy of your speedometer.
The following list contains factors that can affect speedometer accuracy and how to minimize them during calibration.
1. Tire diameter increases slightly as vehicle speed increases. To minimize this error drive at an average speed of 45 MPH (75 KPH) during calibration.
2. Tire diameter increases slightly as tire air pressure is increases. To minimize this error, check the vehicle's tires to ensure correct air pressure.
3. Tire diameter changes with vehicle load. Minimize this error by having an average load in the vehicle during calibration.
4. Minimize tire slippage error by not breaking traction during calibration.
Note: Always recalibrate speedometer after any tire size or differential ratio change.