Ahead of today's second practice session the air temperature is 25 degrees C, while the track temperature is 30 degrees. The sky has a lot more blue patches now, while the risk of rain is 10%.

A damp track limited running in the early part of this morning's session, and it was some time before Sebastian Vettel was the first driver to switch from Inters to slicks.

Having previously opined the track was "too dry", the German was soon complaining that it was "too wet", a fact proven by the other drivers that followed suit in making the switch.

Once things had calmed down, it was business as usual with Lewis Hamilton setting the pace ahead of the Ferraris and Red Bulls.

Despite the grid penalty that sees him demoted to the back of the grid for Sunday's race, Brendon Hartley out-paced Sean Gelael, while Carlos Sainz wasted no time getting the better of Nico Hulkenberg at Renault.

Ricciardo was sidelined for much of the session, but Red Bull insists this was about set-up changes and not a problem with the car, on the other hand Max Verstappen looks likely to need a new engine on Sunday and with it the relevant grid penalty.

Having given over their cars to Sean Gelael and Charles Leclerc earlier, Daniil Kvyat and Pascal Wehrlein are in action this afternoon.

Fernando Alonso was the only driver who didn't post a time earlier, the Spaniard limited to just 4 laps by a hydraulic leak.

The lights go green and Kvyat leads the way, followed by Alonso and Grosjean.

As Kvyat posts the first time of the afternoon (39.733), there's an early spin for Grosjean at T11 who loses the rear end of the Haas.

Alonso posts 39.023 to go quickest as more drivers head out.

Shortly after Grosjean's spin, teammate Magnussen follows suit at T19. For a while it appears as though the Dane is stuck in the kitty litter but he eventually gets going.

A good mixture of softs and supers, as Ocon goes quickest (37.509).

"Can he get out of the way please," asks Magnussen of his teammate who was causing all manner of issues for Verstappen in FP1. "Superbly intelligent of Kevin," says the Frenchman, with just a soupcon of sarcasm.

No sooner has Raikkonen gone quickest (36.667), than Ricciardo posts 36.426. The Mercedes duo go third (Bottas) and fourth.

A 36.328 sees Verstappen go top as, after 13 minutes, Vettel is the only driver yet to post a time or even appear.

Shortly after, Vettel finally heads out, as Ricciardo goes quickest (36.116).

Vettel is off and in the gravel at T19, luckily however he is able to continue. "I think you saw that," says the German. Indeed they did.

Replay shows the rear of the car stepping out for no apparent reason.

He heads back to the pits.

The yellows following Vettel's off wrecked Hamilton's chances of improving, the Briton having been quickest in S1.

Interesting to note that Ricciardo's time was set on the supersofts, as was (4th placed) Raikkonen's, while Verstappen and Hamilton were on softs.

Asked about his helmet, Hartley replies that it is still lifting but better than ever before. And after John Voight in Ray Donovan the other night, that's a route we have no intention of heading down.

27 minutes into the session, Hulkenberg has the track to himself. He makes effective use of the lull, improving his time but remaining 12th (on the softs).

Bottas is the first to make the switch to the ultrasofts, Hamilton following suit.

The Finn immediately goes quickest in S1, maintaining the pace in S2. At the line it's 35.596, quicker than Ricciardo's best (on supers) by 0.520s.

Now Hamilton goes quickest in S1, the Briton also maintaining the pace into the second sector. At the line it's 34.668 which is quicker than last year's pole time (34.999) and 0.6s up on his teammate.

More drivers switching to the pink ultrasoft however, still no sign of Vettel following his earlier off.

Renault reveals an engine issue for Hulkenberg, the German out of his car as it is taken to pieces.

A 35.514 sees Raikkonen improve to third, albeit 0.84s off the pace.

Verstappen splits the Mercedes duo with a 35.065 but is still 0.397s off Hamilton's pace.

Elsewhere, Vettel heads out on the ultras. The German posts 35.192 to go third, 0.524s off Hamilton's best.

Meanwhile, the TV cameras pick up on something falling from Alonso's car as he runs the kerb in the final corner.

Ricciardo improves (35.463) but remains fifth.

Grosjean is clearly struggling, currently 19th and 3.7s off the pace, he complains at the lack of aero balance.

With the qualifying sims out of the way, attention, as ever, switches to the opening stage of Sunday's race as the race sims get underway.

As the cameras close on Hamilton as he performs a practice start at the end of the pitlane, for a horrible moment it appears that they might have caught him at the wrong time. After an excruciating delay he finally gets going and begins his race simulation.

As work continues on Hulkenberg's car, Sainz finally makes the switch to ultras and subsequently posts 36.529 to go 11th.

With Hulkenberg and Grosjean yet to post times on the ultras, Stroll is also having issues, not least with his headrest, a problem that affected Hamilton in Baku.

Vandoorne is warned to avoid the sausage kerbs in the exits, the McLaren one of a number of drivers enticed to use more and more of the over generous run-offs.

Hulkenberg is finally back on track and straight on to the ultras. The German posts 36.534 to go 12th, just 005s off his (new) teammate's pace.

Quickest on the timesheets and quickest on his long run pace, the weekend is off to a great start for Hamilton.

Not so Vettel who is 0.524s off the pace and has only completed 8 laps - compared to the Briton's 20.

Check out our Friday gallery from Austin, here.