When I get pulled over I pull as far as I can off the road, roll down the window, turn off the car, turn on the dome light (at night) and keep my hands on the wheel till the officer comes up. I then will try and beat him to the punch and ask why I was stopped. 9 times out of 10 the officers are nice and there is no reason to go into strict protect your rights mode. Also in PA there is no requirement for me to announce that I'm armed. Armed or not I never make sudden movements and try and keep my hands on the wheel/in view at all times. This includes when the officer goes back to his cruiser.
Remember, just because a question seems polite and reasonable and chatty doesn't mean it is.
"Do you know why I pulled you over?" Sounds good. You can be 99% sure you know why, but shut your yap, or say "NO" then shut your yap.
Unless you are a mind reader you don't know why.
While 'do you know why I pulled you over' sounds reasonable and friendly, the kicker is if you say 'speeding' and then a half minute later realize that hey, you crossed from the 35MPH zone to the 45MHP, and hence weren't speeding, too late you already admitted to it.
Second, you never know for sure why you got pulled over. It might have been 'failure to signal' but if you say 'speeding' and his next question is 'how fast were you going' you just potentially talked yourself into another ticket.
Heaven forbid you say something like "Umm, because you saw me throw a beer can out the window?"
When asked 'do you know why I pulled you over?" I respond with No.
When asked 'why were you speeding? where are you going? etc' I ignore the question and say "What can I do to help officer?" and when asked for my DL "Here is my license officer, I believe everything is current"
You can be reasonable and polite AND maintain your rights. However it sometimes requires you to ignore their question, and ask one of your own instead.
Saying "what can I do to help" seems to work much better for a minor traffic stop than 'are you detaining me?' when the officer starts asking questions hoping you will consent to an information gathering "consensual encounter"
Others like 'I've given you my proof of insurance already, right?' (asked in a non-sarcastic way) is another way to ignore a probing question without coming off like an a-hole.
And it need not be a TOTAL information blackout. Last time I was pulled over for supposedly rolling through a stopsign (I didn't)
Officer asked me 'can you roll down your window' I pushed the button and the window twiched but didn't go down. I said 'Sorry, it's frozen, does that sometimes when it drizzles then gets colder'
Then I did my 'Do you know why I pulled you over?' No (even though my brain said 'yes, it is saturday night, 11 pm, you are seeing if you can smell beer on my breath, but I haven't been drinking) and 'So where are you going?' to which I replied 'Lets see, I gave you my insurance card already, right?'
and to "Why are you in such a hurry tonight?" with "What can I do to help officer?"