http://www.flickr.com/photos/27199844@N07/4458677308/
this is a excellent example to show all the 60mph = 100km/h thinker and it makes no different at all
look at this test numbers
15.3s 0-140km/h(86.99mph)
15.8s 0-142.2km/h (88.3mph)
a different of only 1.31mph gets you a time gap of 0.5s
and the different between 60mph and 100km/h is 2.13mph!!!!!!!!!