If they want to search your car, they will find reasoning that justifies their actions.
A decision handed down by the US Supreme Court pretty much gives the police the okay to search your vehicle with little to no real justification. Seems that being arrested for speeding is all they need to search your car.
I wish that was being sarcastic. Sadly, I'm just stating the reality of life in the US post 9/11.
Actually, the "weapon" they found, a rusted roofing hatchet, was their pretext to search, not the speeding.