What constitutes a tyre change?

[hollus]

My excuses if there if this has been discussed already.

I am wondering what exactly counts as a tyre change...and its consequences for extreme strategies.

From the sporting regulations:
"25.4) Use of Tyres:
e) Unless he has used intermadiate or wet tyres during the race, each driver must use at least one set of each specification of dry-weather tyres during the race"

Now, what exactly is "use" by the wording of the rules, as I don't believe in spirits. Is "use" one lap? Is it crossing the finish line? Is "use" rolling? Is it having them in the car?

All this talk of how difficult it is to overtake (in Bahrain!) got me thinking. If we take Monaco or Hungary, passing on track is effectively off under most circumstances. Now, I start the race in the softs, from the pit lane. Not from the end of it, but from my box. I roll 1 meter on them, stop, get the hards on. Have I "used" my softs? Am I now allowed to finish the race without any firther pit stops? I am last, but everybody else has to pit, and honestly, most will do it in the second lap after the safety car came out... am I now winning the race?

[Dukeage]

I imagine use constitutes leaving the pit lane limit zone with them on, as that's what usage is defined as for an engine. If not, it could be possible, depending on your pit stall position, to drive the whole race on one set of hards, pit in on the final lap, switch to softs and then cross the line, but if it's done like engines that's a disqualification.