Off the back of an eventful sprint race, Formula 1 teams are braced for high tyre-wear race at the United States Grand Prix.
Given Austin's varied and demanding high-downforce layout, the new track surface and high temperatures, tyre wear and graining concerns could open up strategy variations of the expected two-stopper using medium and hard tyres.
Two-stop looks king
Pirelli doesn't consider the soft tyre particularly usable, other than for late fastest lap glory runs, with a two-stopper on medium and hard tyres the clear winner in its simulations. The medium tyre is around 1.2s quicker than the hard compound, making it by far the best tyre for the 56-lap race.
"The medium compound will be the protagonist of the race because teams have one set of hards and a lot of sets of mediums," Pirelli's head of motorsport Mario Isola explained.
"We know that the soft is not really suitable for the race, unless you want to try a fast lap. The tyre wear is higher than expected. That is also the reason why the race will be two-stop. We do not predict any one-stop strategy, because it's really marginal in terms of wear.
"Medium, hard and medium again is the quickest on paper. If you want to do something different, you can do medium, medium and hard at the end. Any other combination, you could start on the soft with a very short stint at the beginning, but to be honest I'm not sure it's going to be popular."
Teams to exploit powerful pitstop undercut
Another reason why a soft-tyre start isn't as tempting is because tyre warm-up on the mediums proved rapid in Saturday's 19-lap sprint. After the Turn 1 hairpin, the demanding Esses ensure that Pirelli's medium rubber is up to speed fairly quickly.
Starting on hard tyres would put drivers at too great a risk of losing track position, but it might still be an option for those starting out of position at the back, like Mercedes' Lewis Hamilton and RB driver Liam Lawson, in a bid to do something different.
But with most teams likely gravitating towards a very similar strategy, the effect of the undercut will be very powerful. Pitstops, in-laps and out-laps are set to be particularly crucial at COTA, although drivers can also pay a price for overstressing the tyres early in a stint, a trademark of this generation of Pirelli rubber.
"I believe that the undercut will be quite powerful, it's an element that you can use in your strategy," said Isola.
"On Saturday they started on mediums and started pushing immediately. The big difference is that in the race they have a fuller tank. If you overload the medium in the first couple of laps, then you initiate degradation that is higher because of the additional weight."
All eyes will be on how polesitter Lando Norris will fare after McLaren struggled with tyre wear in the sprint, and Norris was somewhat lucky to claim pole after a late yellow flag denied Red Bull's Max Verstappen and Ferrari man Carlos Sainz a second run, with both drivers appearing ready to challenge for pole.
When asked how big a concern tyre wear is for McLaren, Norris replied: "Quite a big one. I don't want to do [that sprint race] again. I think we improved the car quite a bit. We're still a bit off, but we're in a good position.
"It's going to be a tough race. Ferrari was very quick in the sprint race with the degradation. Max is Max, and they're going to be fast. So I'm excited. I think it's going to be a good battle and probably a good one to watch."
COTA's diverse layout to cause graining headache
The first half of the Circuit of the Americas features a string of demanding corners that overheat the tyres, followed by a long straight to cool them down, which makes managing both overheating and graining on both axles something to be wary of as drivers work to keep the tyres inside the operating window.
"This circuit has a bit of everything," Isola nodded. "Setting up the car properly for a long stint is probably more complicated than other circuits that are all stop-and-go.
"You can see on the tyre surface that in some cases we had some graining on the front, in other cases on the rear. That means that probably the set-up of different cars is not the same, and some teams decided to protect a little bit more the rear than others."
Sainz added: "[Our rivals] haven't stood still and they would have improved that front graining that a lot of people were struggling with in the sprint. I think the field is going to be very close and it should be an exciting race between a few cars."
