Speedo Accuracy

The accuracy of vehicle speedos is covered by Australian Design Rule 18. Until July 2006 this rule specified an accuracy of +/- 10 percent of the vehicle’s true speed when the vehicle was travelling above 40km/h.

That is, at a true vehicle speed of 100km/h the speedo was allowed to indicate between 90km/h and 110km/h.

An odometer accuracy of +/- 4 percent was also a requirement.

From 1 July 2006 newly introduced models of a vehicle available on the market must comply with ADR 18/03. Also, from 1 July 2007 any newly manufactured vehicle (excluding mopeds) must comply with this rule.

This new rule requires that the speedo must not indicate a speed less than the vehicle’s true speed or a speed greater than the vehicle’s true speed by an amount more than 10 percent plus 4 km/h. Significantly, this change means that speedos must always read 'safe', meaning that the vehicle's true speed must not be higher than the speed indicated by the speedo.

That is, at a true vehicle speed of 100km/h the speedo must read between 100km/h and 114km/h. An alternative way to look at it is; at an indicated speed of 100km/h, the vehicle's true speed must be between 86 km/h and 100km/h.

Significantly, this change means that speedos must always read ‘safe’, meaning that they are not permitted to read lower than the actual speed of the vehicle.

Additionally, there is now no requirement to have an odometer, and therefore there is no accuracy requirement.

This change was made to align Australian vehicle rules with those already in place in Europe.

Note that some vehicle manufacturers chose to comply with the new rule before 1 July 2006. This is acceptable.