Inaccurate speedos in new cars drive me to distraction. It's not accidental, nor is it an effect of tyre wear. Each maker picks an error that they like, and you're then stuck with it.
Land Rover/Range Rover, it's 3% plus 3 kph. VW about 7% above 60 kph. Audi about 3%. GMH were about 6% last time I measured one. The cars know their true speed too. In the VWs it was possible to input odd codes to the entertainment system, and you'd get a readout of the true speed...on the heating display.
The upshot of this is that we get mobile road blocks, driving along in the right hand lane of our freeways, blithely blocking everyone else. Their speedo reads 110 kph, but they're really doing about 103. They won't move over, 'cos they think they are in the right, and you're a filthy speedster.