Odometer Policy (TIPS 0201-08)

ODOMETER POLICY

TECHNICAL INFORMATION TIP - MANUFACTURER

DESCRIPTION

(08) ODOMETER POLICY

The Technical Support Line occasionally gets call concerning odometer accuracy. Below is some information that you should find helpful when addressing a customer concern of this matter. Also refer to Technical T.I.P.S. dated 01/95 for additional information concerning odometer testing.

The automotive industry generally follows standards for speedometer and odometer accuracy as set forth in SAE (Society of Automotive Engineers) Standard J862. According to this Standard, "the odometer records actual distances traveled within +/- 4% at 20, 40, and 55 mph." Tolerances such as this are acceptable due to the finite usable number of gear teeth on the ring and pinion drive assemblies and other measurable factors. One example of another of these factors is also found in SAE Standard J862.

With regard to road speed, a tire may experience as much as a 3% change in revolutions per unit of distance from 30 mph to 90 mph due to a change in rolling radius caused by centrifugal force. Yet another variable to consider is that a speedometer is calibrated at room temperature by the instrument manufacturer. SAE Standard J678 outlines recommended calibration tolerances for the instrument itself. But, consider how often a vehicle is operated outside the parameters of "room temperature."

Considering the factors which affect odometer readings (takeoff pinion design limits; tire make, tread and construction; inflation pressure; tire growth; tire size; centrifugal effects; operating temperature; and load increase on rear axle) a certain degree of tolerance is to be expected.