The Circuit of the Americas is all about variety: both in terms of the demands placed upon the tyres throughout the lap and the weather conditions expected during the course of each day, as well as the weekend as a whole.

Between the first and second free practice sessions, ambient and track temperatures rose by six and 16 degrees centigrade respectively. This important difference has a profound effect on the behaviour of the P Zero White medium and P Zero Yellow soft compounds that have been nominated for Austin. This is a step softer than the medium and hard tyres that have been used during both previous occasions that the United States Grand Prix has been run at the Circuit of the Americas.

Weather conditions tomorrow are expected to be much cooler than they were today, with a high of just 19 degrees centigrade forecast.

So far, there is a performance gap of approximately 1.3 seconds between the two compounds, on one of the longer circuits of this year's grand prix calendar. In the afternoon session, wear and degradation was higher than it was in the morning, meaning that teams will have to take a flexible approach to strategy, with the correct tactics providing an opportunity to gain track position.

Mercedes driver Lewis Hamilton was quickest during both free practice sessions today, using the medium tyre to set his best time in the morning and the soft to go fastest in the afternoon, with a benchmark time of 1:39.085s; just 0.003 seconds faster than his team mate.

Paul Hembery: "In the three years that we have been racing at Austin, the track has definitely evolved to provide more grip - and we saw further track evolution during the course of today, exacerbated by the wide variety of temperatures that we were running in. We're expecting a similar variation in temperatures for the rest of the weekend, including conditions that might be a lot cooler for qualifying tomorrow. From what we can see so far a two-stop strategy looks to be the most likely, but also with the potential for some mixed strategies going down the grid, depending on track position."

Check out our Friday gallery, here.