The FIA has also clarified the tyre rules as follows
25.4 Use of tyres :
Tyres will only be deemed to have been used once the car’s timing transponder has shown that it has left the pit lane.
a) Three sets of dry-weather tyres will be allocated by the FIA technical delegate to each nominated driver for use during P1 and P2, two of “prime” specification and one of “option” specification. These are the only dry-weather tyres which may be used during these sessions.
One set of “prime” specification must be returned to the tyre supplier before the start of P2 and one further set of “prime” specification and one set of “option” specification before the start of P3.
If an additional driver is used (see Article 19.1(b) he must use the tyres allocated to the nominated driver he replaced.
b) Eight further sets of dry-weather tyres will be allocated by the FIA technical delegate to each nominated driver, four of each specification, for use during the remainder of the Event. However, one set of each specification must be returned to the tyre supplier before the start of the qualifying practice session and may not be used during the remainder of the Event.
c) Prior to the start of the qualifying practice session intermediate and wet-weather tyres may only be used after the track has been declared wet by the race director, following which intermediate, wet or dry-weather tyres may be used for the remainder of the session.
d) At the start of the race each car which took part in Q3 must be fitted with the tyres with which the driver set his grid time. This will only be necessary if dry-weather tyres were used to set the grid time and if dry-weather are used at the start of the race.
Any such tyres damaged during Q3 will be inspected by the FIA technical delegate who will decide, at his absolute discretion, whether any may be replaced and, if so, which tyres they should be replaced with.
e) Unless he has used intermediate or wet-weather tyres during the race, each driver must use at least one set of each specification of dry-weather tyres during the race.
If the race is suspended and cannot be re-started, thirty seconds will be added to the elapsed time of any driver who was unable to use both specifications of dry-weather tyre during the race. However, any driver who completes the race without using both specifications of dry-weather tyre will be excluded from the race results.
f) If the race is started behind the safety car because of heavy rain (see Article 40.14), or resumed in accordance with Article 42.5(a), the use of wet-weather tyres until the safety car returns to the pits is compulsory.
courtesy of www.fia.com