Maybe your speedometer was off.New gears or bigger wheels will do that.I remember once i saw a few cops at night with their light out on the side of the road,and i figured i'd step on it alittle just not too much.So i did,i think i was driving around 55mph in a 45mph zone.And next thing i know is he's pulling me over telling me i was driving 57in a 45 zone.And i have a speedcalibrator.But he also said."I'm not going to give you a ticket now.If you were driving over 60mph then i woul have given you a ticket.This time i will let you off with a warning."I didn't wanna push my luck,so i said."Thank you" and i was on my way.That was the second time that a police officer let me go off with a warning.They're people themselves afterall,and most of them are really nice guys.As long as you don't step on their toes.
Since then i eather drive only alittle faster then the speedlimit,or i drive as fast as everyone else.with the occasional speedup to get infront.I dunno why,i just like to be ahead.