I got 285/30 falkens on my fg2 ute and some online calculator said they were 3% taller than my stock tyres. So I have been wondering what that's done to my speedo accuracy. I plugged in a tomtom yesterday when we went to mandurah to pick up the missus new Mondeo thing and the speedo now reads about 2% low. That is at 100 indicated, tomtom says 102, at 110 indicated, tomtom says 112. 60 indicated is 61, 70 is 71, 80 is 81-82. So there you go.