Is your speedometer lying?
 

I have the 2009 Mazda 5 GT for 3 weeks now and today I compared the speed indicated on my GPS to the one shown by the speedometer. Looks like the speedometer indicates the car is going 105 km/h when the GPs shows only 100 km/h. 5% is a lot, I will rake the milleage on the odometer faster than normal, with all the issues that come from this: depreciation, out of warranty faster...

Please check your readings and let me know if you experience the same problem.

Due to the idiosyncratic way the laws that govern vehicle odometers and speedometers are written, many car manufacturers have speedometers that are optimistic while the odometers are spot on. If I recall correctly, both Canada and the U.S. laws state that the speedometer has to be within 7%, however, the odometer has to be within 1% (or something very near that point).

As a suggestion, use your GPS to calculate the kilometers driven and compare it to your odometer, my guess is that you'll find them to be pretty close.

The same goes for the UK with respect to speedos. My 2008 Mazda5 sport shows higher on clock than on GPS's (stand alone Pocket PC based navigation with different receivers). for example clock says 140 GPS says 127. This is for various reasons I wont bore anyone with.

That can't possibly be MPH......I thought the 5 was restricted ;-)

I was abroad (Europe) on mostly 4 laned roads. It left the Mercs, BMW, Audi etc in the rear view mirror. Only equalled by a sporty VW Golf for a while for some miles before he turned off. Now I don't want to be flamed about this, (the cars or the speed) I know the law and I chose. But nothing overtook me during my time in Europe (not counting the few crazy people in the Alps around Austria and Italy and the Carpathians in Romania. But as soon as it was dual carriage way going up again they were behind us again. This 2 litre car is very capable. Just a great shame about the front wheel geometry on the 17" wheeled versions (2008/09).