Hi, do have the original wheel/tyres on the car? as non originals will affect the speedo accuracy, by law the speedo must be within 10% at 30mph ie +/- 3mph but at 70mph the error could be anything, if your comparing the speedo against a gps system the gps will always lag behind the speedo as it updates its speed at a slower rate than the car speedo, as your car has an all electronic speedo, the speed sensor on the gearbox sends its info to the engine ecu which sends it to the speedo pod, recalibration is possible with the correct diagnostic kit (main dealer)
nigel, August 2008
