Why Mexico practice is mixed up

Sometimes, Formula 1 free practice performances are more clear-cut than others. On Friday in Mexico, Ferrari was fastest on single-lap pace, Force India on adjusted single-lap pace, Mercedes on super-soft and soft Pirelli long-run pace and Red Bull based on medium long runs.

You could argue this is all meaningless, but dig a little deeper and it reveals some fascinating characteristics of the Mexico City circuit, and answers some of the questions posed by a glance at the fastest laptimes of the day.

There were a few conditions that made Friday's running unusual. Firstly, the anticipated evolution of the track since last year was non-existent, much to the surprise of Pirelli and the teams. While the track is evolving and will continue to during the race weekend, the asphalt remains in a similar, low-grip state to last year.

Secondly, the weather. The track temperature was only 35C at its highest, which was lower than expected. This contributed to the tyre graining, more of which later, and will continue to be significant throughout the weekend as it isn't expected to get any warmer.

Almost everybody set their fastest time on Friday using the super-softs, with the exception of Nico Hulkenberg, who set an eye-catching time using the softs in the afternoon session.

Single-lap pace

1 Ferrari (Vettel), 1m19.790s
2 Mercedes (Hamilton), +0.004s
3 Red Bull (Ricciardo), +0.658s
4 Force India (Hulkenberg), +0.784s (softs)
5 Williams (Bottas), +0.839s
6 Toro Rosso (Sainz), +1.184s
7 McLaren (Alonso), +1.213s
8 Renault (Magnussen), +1.652s
9 Manor (Wehrlein), +2.190s
10 Sauber (Ericsson), +2.207s
11 Haas (Grosjean), +2.618s

With a difference in pace of nine-tenths between the super-softs and the softs that bodes very well for Force India. That said, track evolution and timing perhaps flattered Hulkenberg's time, which was certainly very good but not hitting it out of the ballpark even though, if you adjusted for the tyre delta, he was quickest.

On long-run pace, the super-softs proved to be very troubling. Front graining was the problem thanks to the low-grip surface, with the tyres sliding around, particularly when not up to temperature, and damaging the compound. Based purely on this evidence, you wouldn't be very confident in the super-softs in race conditions.

The list below is based on a run of six laps, unless stated otherwise. Force India is not included, as its drivers didn't use super-softs during FP2.

Long-run average pace on super-softs

1 Mercedes, 1m23.897s
2 Williams, 1m23.915s
3 Ferrari, 1m24.131s
4 Red Bull, 1m24.455s
5 McLaren, 1m25.127s (five laps)
6 Renault, 1m25.202s
7 Toro Rosso, 1m25.203s
8 Haas, 1m25.335s (four laps)
9 Sauber, 1m25.455s (four laps)
10 Manor, 1m26.151s

But there is one big caveat: track evolution means that the graining could well reduce and the super-softs could be back in the game come Sunday.

"What I expect is that, during the weekend - if it is not raining - we will have a big track evolution and the super-soft could work better," said Pirelli racing manager Mario Isola.

"This is probably the secret for the race, because if we consider the level of degradation we have now on the super-soft, it's quite high. But it's mainly due to graining.

"If, during the race weekend, they are able to reduce the graining the super-soft also becomes a good race tyre. So this is a different situation to Austin where the super-soft was a very aggressive choice and people were trying to qualify in Q2 on the soft."

The soft compound, of course, also suffered from graining. Below are the long-run times on the softs for all teams that ran them based on six laps of data per car. The softs lasted far better than the super-softs despite also graining.

Long-run pace on softs

1 Mercedes, 1m23.269s
2 Toro Rosso, 1m24.154s
3 Force India, 1m24.211s
4 Renault, 1m25.341s
5 Haas, 1m25.536s
6 Manor, 1m25.572s
7 Ferrari, 1m25.789s

Ferrari's pace, which is based on Kimi Raikkonen's run, is not to be taken too seriously and is included for the sake of completeness. It was erratic and definitely not representative.

But, again, what this shows is that Mercedes is looking strong.

Long-run pace on mediums

1 Red Bull, 1m23.603s
2 Mercedes, 1m23.994s
3 Force India, 1m24.144s
4 Ferrari, 1m24.211s
5 Williams, 1m24.285s
6 McLaren, 1m24.637s
7 Toro Rosso, 1m24.647s
8 Sauber, 1m25.447s
9 Renault, 1m25.818s
10 Manor, 1m25.833s

With the medium tyres showing degradation levels that are as good as zero, and looking easily good enough to last to make a one-stop strategy possible, the medium is a very credible race tyre.

Crucially, Red Bull's pace suggests that Max Verstappen's claim that its "short-run pace was not representative" is correct. Daniel Ricciardo accepted Red Bull didn't have the perfect day on the long runs either, but there's certainly more to come from Red Bull.

SO WHAT DID WE LEARN?

While Ferrari's headline pace was impressive, there's nothing in the long runs to suggest it's going to be dramatically more competitive here than usual.

Mercedes should have the advantage, and with the pace Red Bull showed on the long runs on medium, there's every chance it will be pushing to get back ahead of Ferrari as the weekend goes on.

But perhaps the most valuable lesson is that at this unusual circuit at an unusual altitude with a surface that is going to evolve rapidly through Saturday and Sunday, the teams are aiming for a moving target. Those who thrive will be the ones who adapt and anticipate conditions the best.

As for strategy, a one-stopper using the softs and the mediums is certainly possible, with a two-stopper starting on the super-softs followed by two soft stints the other option. But with the super-softs potentially coming into their own later in the weekend, things could change.

Then again, with rain on the horizon for Sunday, this all could mean nothing come race day.

HIGH-ALTITUDE CHALLENGE

With Mexico City at an altitude of 2250 metres (over 7000 feet) the air density is dramatically lower than at a usual race - last weekend's United States Grand Prix at 129 metres above sea level.

This means cars run high levels of wing, but with the downforce produced more akin to Monza. Autosport's technical expert, former Jordan and Stewart/Jaguar technical director, Gary Anderson explains.

"With the same wing set-up, it's just a loss of downforce and drag proportionate to the percentage air density loss, which is roughly 20%," says Anderson.

"But what you have to remember is that the cars will be travelling faster because the drag is reduced, and the turbo power units won't lose any power so the downforce will be brought back at top speed.

"An example would be that if they were running Hungary-type wing levels, which gives a top speed of 300km/h and a maximum of 2000kg at that speed, you multiply that by 0.8 for the lower density.

"That gives you 1600kg. Then, at 350km/h in Mexico, you will still have 2170kg downforce even with the thinner air at top speed, if you do your sums."

That means the drivers face an interesting challenge, with relatively normal downforce levels when they stamp on the brake at over 360km/h on the approach for Turn 1, then proportionately lose more downforce as the speed reduces.

This just adds to the challenge of an unusual circuit, which is looking set to create an interesting weekend - even if Mercedes can be expected to be top dog yet again.