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What really happened with Miami’s F1 track surface

The unique surface did not win over many fans among the drivers, with some claiming that the racing suffered because it was so dirty offline that they could not risk overtaking moves.

But while things were certainly far from ideal, and improvements will no doubt be sought for F1’s return next year, in the end the race was not as bad as some drivers like Sergio Perez had feared.

In fact, Fernando Alonso actually spotted how much more grip there was than expected at the outside of Turn 1 on the drivers’ parade, prompting his first corner to emerge. Later on Charles Leclerc was caught out by Max Verstappen being able to brake so late there later on when the Red Bull driver took the lead.

Mercedes boss Toto Wolff felt the nature of the surface – and even some repairs that were needed over the weekend – had been good for the spectacle.

“Even the track breaking, Turn 17 for example, gave great racing,” he said. “It was very difficult to brake into Turn 17.

“If you lost the line then you lost a position or two, and it’s clear that the drivers will say: ‘well that’s not optimal.’ But for racing and entertainment it was great stuff.

“It’s almost like a trick gravel bed that you need to put in there to make for exciting action. All in all, I would say for a first event, nine out of 10.”

An unusual surface for F1

What stood out for many is that F1’s other new circuits – like Jeddah – have delivered surfaces that have produced great grip and no problems through their inaugural events.

Comparisons with Jeddah need to be cautioned, however, because it is a night race that takes pace in cooler conditions that automatically offer much better surface grip.

Miami’s track temperatures were some of the highest we’ve ever seen in F1, so the feel of it for the drivers was always going to be different.

Turn 17 track repair detail

Turn 17 track repair detail

Photo by: Adam Cooper

There were questions prompted though about why Miami had not used the same materials as elsewhere in its construction.

The matter also got further clouded when some resurfacing work was needed before track action began on Friday, which then further clouded the real issue at stake.

That damage had actually been caused by the machine that had been used to blast the bitumen from the surface being put into a wrong setting and dropping hydraulic fluid on to the track.

This has caused the surface to break up when cars first ran on it, but it was something that would have happened at any other venue where the same accident had occurred.

In terms of the composition of the Miami track surface, it is different to what is used at other F1 venues.

However, due to its location, there are strict government guidelines in place from the Florida Department of Transportation (FDOT) which dictate that certain materials – some of which have to be local – must be used in the composition of any surfaces laid.

As David Woodward, from F1 track specialists R3 that helped lay the Miami track, stipulations placed on the venue were unlike anything laid down elsewhere.

“We had to use local materials, local aggregates, we had to use local asphalt companies, and we had to work within the requirements of the local FDOT and what they ask about their local materials,” he said.

“So it was a pretty difficult brief in one respect because we had to come up with something that was maybe a little bit different from your typical F1 track.

“At an F1 track you have a much wider range of aggregates and asphalt materials, whereas here we were stuck with the FDOT material, and we were stuck with the local aggregate, so it was a lot more challenging in one respect.”

The end result was the use of a lime rock aggregate, combined with a 60% US-mined granite mix from Georgia, to try to come up with a surface that worked well for F1.

Turn 17 track repair detail

Turn 17 track repair detail

Photo by: Adam Cooper

Normally, lime rock is not widely used in F1 tracks because it breaks down too easily and it polishes – so therefore it doesn’t offer good grip nor decent tire degradation.

However, the southern Florida lime rock has slightly different characteristics. Its high silica content is akin to a texture that is like small shards of glass, so as it breaks down when cars run over it, it exposes more of this silica that offers decent grip.

The theory was that this unique combination would therefore work – with the silica shards overcoming the normal downsides of using lime rock.

This explains why Pirelli’s analysis of the surface over the Miami weekend showed it to be very smooth on a macro scale, but rough on a micro scale.

Pirelli’s F1 chief Mario Isola said: “In terms of numbers, this asphalt was different from the others because the macro roughness was very, very low, but the micro roughness was I believe the highest of the championship.

“So the level of grip was good since the beginning with, obviously, a lot of track evolution.”

However, what appears to have taken place is that as the surface got steadily chipped away by the F1 cars, the small stone fragments that come away have to go somewhere.

Pirelli found over the Miami weekend that the tires were coming back to the pits with stones on them; and that meant there would have been plenty out on track and offline too.

Isola added: “The cars are taking off some small stones from the asphalt. Some stones are coming off, because we found the stones on the tires, and these are obviously offline. And when you’re run off the line, you lose a little grip.”

Things did improve over the weekend though. What was a quite extreme situation on Friday, as the first stones came away, was greatly improved over the weekend, especially thanks to the extensive use of a FOD Boss track sweeper machine.

The Safety Car on track

The Safety Car on track

Photo by: Mark Sutton / Motorsport Images

What is critical to understand now is how the track will react to a year of weathering, having now had its first GP.

Will the phenomenon of the small shards breaking away disappear over time as the surface is used more, so the problem naturally cures itself? Or is it something that will require a revamp of the surface?

That is something that will only be decided as part of the Miami GP’s post-race analysis.

But it is clear track chiefs are on top of things and have vowed to do whatever it takes to ensure the race is as good as it can be in 2023.

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