I saw some research done a couple years ago that showed that at 60mph, most USDM cars (from a wide range of manufacturers) indicated anywhere from 2-5mph higher. So say it's 4-5mph, that will make about a 10mph difference at 130, showing 140. Not to mention discrepancies in PSI, tire wear, aftermarket wheels and tires (or even stock replacement tires on stock wheels). Two tires stampted the same size from different manufacturers will even show discrepancies. Add up all these variations over 100mph and things get a little out of wack.