I know there have been a few on here worried about the effect of larger wheel and tyre sizes on the accuracy of their speedo and, if like me, you live in Yorkshire the Po Po do love their rays guns (at least they publish where they will be hiding each week though).
If you have a Smart phone, Android or Apple, there are free apps for GPS speedometers which you can download such as this one.
https://itunes.apple.com/gb/app/speed-tracker-free.-gps-speedometer/id604836034?mt=8
Tried it myself over the last couple of days and it's not too bad.
13 Jan 2014, 11:25am