If you answer directly, it should be to say "I only know what my speedometer displays." And then politely decline to mention the number it had been displaying. If you say a number, in the cops eyes, you are either lying or confessing. If you just say "yes", you cut off certain affirmative defenses you could otherwise raise. If you say "no", the cop may charge you with reckless or inattentive driving rather than speeding. There is literally no way to answer that question that can help you, the best you can do is say the thing that hurts you least.

The answer that you should train yourself to give is "I do not consent to searches, seizures, or questioning without the assistance of legal counsel. Am I free to go? If not, why am I being detained?"

The same response covers all police questions in the US. You can repeat the entire thing on subsequent questions, or you can shorten it to "I don't consent to questioning without the assistance of legal counsel." You have to train yourself. Your natural instinct will be to present as nonthreatening and cooperative. You need to be nonthreatening and unimaginably stubborn. If you have ever seen the television show "COPS", very nearly every "guest star" just talks himself right into a trip to jail. Almost every episode is a variation on this:

  COP: Sir, can you think of any reason why I should arrest you tonight?
  Dumb-Assed Suspect: I have drugs in my pocket.
  COP (to DAS): Put your hands behind your back.
  [COP handcuffs DAS and performs a search.]
  COP (to camera): He just gave us reasonable suspicion, so I searched him and found drugs.
  He's going to jail now.

Don't be that guy. After you give your canned response, one of several things should happen. The cop realizes you're going to be actual work, and releases you with a stern warning, so he can pursue easier marks. The cop realizes that he gets overtime pay for appearing in court to testify, and you might go to trial, so he issues the summons. The cop gets personally offended at your "constitutional bullshit" and actually arrests you on a "contempt of cop" pretext charge, which will vary by jurisdiction. This is a punitive inconvenience for you, but you can then launch a civil suit that will probably pay out, after you consult with a civil rights attorney.

If you have any inkling it might go down the third way, it would be wise to record the entire encounter and make public records requests for any recordings the police may have in their possession as soon as you possibly can. And you should have such an inkling. So record every police encounter, always. If it's a routine encounter, you can always delete the video, but if it goes bad, you can't magic up a recording out of thin air.