Allow for a 10% flexibility open road speed in New Zealand

Allow for cars that use public open roads a 10 % flexibility in open road speed limits of 100 kmh.
the main reason for this is that car speedometers are not as accurate as the law allows for. A near minimal tread tyre versus a new tyre can be as much as 2% out so what are they calibrated to. A different brand or fitment of tyre can be up to 5% out in speed reading. Due to circumference variations. The speedo can be 1% out from factory on all new cars. Together with the fact that it often is not possible to maintain this tolerance down hill or when passing slower motorists.The police radar can be 1-2% out. All these measures and factors make it impossible to limit vehicles to the 1% tolerance.