You: "I wasn't going fast. I was driving at a safe and prudent speed given the conditions."
ADD: It is good to know if the state you are in or states your frequently drive in is/are "Maximum Speed Limit" or "Presumed Maximum Speed Limit" state(s). I grew up in Minnesota which is a "Presumed Maximum Speed Limit" but now live in WI which is a "Maximum Speed Limit". The nice thing about Minnesota and "Presumed Maximum Speed Limit" is that if you are on a highway outside of a municipality (so in a township) then the posted speed limits are only presumed to be the maximum speed limit. Going faster is prima facie evidence of going to fast and allows officers to stop you. However, if you choose to fight the ticket in court, you can admit to going faster than the posted limit and argue that you were still driving a safe and prudent speed given the conditions. So, if you were in the country driving 65 on a straight and level road with a posted speed limit of 55 on a clear, dry day with 10+ miles of visibility and no other cars on the road, people or animals int he ditch or near the shoulder and a cop caught you on his laser device sitting 1/2 mile down the road, assuming you slowed down to 55 mph before getting close to him, you could argue these facts in court and argue that "the facts and outcomes speak for themselves"... no one was harmed or injured showing again that the speed of 65 mph in those conditions and circumstances was in fact still safe and prudent. In Wisconsin, if you admit to going over the posted speed limit anywhere, you're guilty of not driving a safe and prudent speed no matter what.
I couldn't figure out why the downvotes so fast, but after reading my reply I think I get it. Because my reply suggested talking to the police. If so, you're are correct, I take back my suggested response above. It only can clue in the officer to note any and every adverse condition regarding the stop. Saying instead "I don't believe I was going fast." is the most one should say in a reply to the question "any reason you were going so fast?"
Downvotes perhaps because lying to a cop, or resorting to yes-it-is-vs-no-it-isnt with authorities is stupid. He stopped you, and has far more weight in court regarding whether conditions were safe for that speed than you do. Doing 54 in a 40 is fast, and neither the cop nor judge will agree with your assessment.
Cops may let you go faster, and they're authorized to do so if conditions fit ... but they also get to say "the speed limit is a limit" and charge you accordingly. There are a few areas where speed limits are broadly understood, even codified, as suggestions (they post limit signs to elicit federal funds, but on a dry sunny day all they care is you can stay on the road and can stop in time), but nearly everywhere else just realize speed limits are just that, and if you violate them don't be surprised if the jurisdiction decides to profit off your actions.
You: "I wasn't going fast. I was driving at a safe and prudent speed given the conditions."
ADD: It is good to know if the state you are in or states your frequently drive in is/are "Maximum Speed Limit" or "Presumed Maximum Speed Limit" state(s). I grew up in Minnesota which is a "Presumed Maximum Speed Limit" but now live in WI which is a "Maximum Speed Limit". The nice thing about Minnesota and "Presumed Maximum Speed Limit" is that if you are on a highway outside of a municipality (so in a township) then the posted speed limits are only presumed to be the maximum speed limit. Going faster is prima facie evidence of going to fast and allows officers to stop you. However, if you choose to fight the ticket in court, you can admit to going faster than the posted limit and argue that you were still driving a safe and prudent speed given the conditions. So, if you were in the country driving 65 on a straight and level road with a posted speed limit of 55 on a clear, dry day with 10+ miles of visibility and no other cars on the road, people or animals int he ditch or near the shoulder and a cop caught you on his laser device sitting 1/2 mile down the road, assuming you slowed down to 55 mph before getting close to him, you could argue these facts in court and argue that "the facts and outcomes speak for themselves"... no one was harmed or injured showing again that the speed of 65 mph in those conditions and circumstances was in fact still safe and prudent. In Wisconsin, if you admit to going over the posted speed limit anywhere, you're guilty of not driving a safe and prudent speed no matter what.
IANAL, but this book was an eye opener: http://www.amazon.com/gp/product/1413312519/ref=as_li_tl?ie=... (affiliate link) save your money though and borrow it from the library.