While road car tyres have gradually grown in width and reduced in sidewall height, Formula 1 doggedly stuck to its 13-inch wheel sizes for decades, chiefly for political and economic reasons.
The history of F1 tyre sizes and aspect ratios – the relationship between sidewall height and contact patch width expressed as a percentage – is as complex as it is convoluted.
Rewind to 1985: Goodyear enjoyed an effective monopoly on 13-inch tyres that extended – sporadic competition from Pirelli aside – until 1996. The US brand saw no reason to follow road car trends simply to beat itself.
Then along came Bridgestone in 1997 and suggested lower profiles, only to be rebuffed by a Goodyear afraid of losing its advantage. Two years later Goodyear departed, and Bridgestone – now the de facto sole supplier – applied the same arguments when Michelin entered F1 in 2001. After the French company departed six years later Bridgestone was awarded the first official FIA sole tyre supplier contract, and simply carried over its rubber through to the end of 2010.
Pirelli replaced the Japanese company in 2011, but so rushed was the process that F1 had no choice but to stick to 13-inches. Each subsequent tender specified the same dimensions, primarily due to team reluctance to shift from their collective comfort zone.
F1’s ‘new era’ tender, however, specified 18-inch rims with reduced aspect tyre ratios – seven years after WEC and Formula E (and other series) switched to low profile tyres. Pirelli and Hankook applied for the F1 deal, the former winning an extension of its contract.
The wheel sizes formed an integral part of F1’s overhaul of its technical regulations package which was planned for 2021, but delayed by a year due to Covid-19. This afforded Pirelli useful additional development time. Track testing was, though, placed on the backburner due to costs and the 2020’s punishing schedule – 17 rounds in 160 days – and Pirelli’s contract extended a year.
The decision to move to low profiles had, though, been taken “five or six years ago in the interests of modernity and (road) relevance” a source with knowledge of the process told RaceFans, but delayed until a revised technical package was introduced as teams had been promised regulatory stability until end-2020.
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Apart from aesthetics, the advantages of larger rims and lower sidewall heights include more direct response to steering and braking input, greater control over spring rates as the ‘jounce’ of high sidewalls is reduces, and increased brake disc area and therefore potentially improved stopping power – in turn facilitating ceramic (or other) braking technologies as F1 strives to phase out carbon friction materials.
Given the flak Pirelli attracts from drivers, teams, fans and the media – even though the company delivers products which degrade as per the ‘target letters’ issued by the teams, F1 and FIA – the Italian company knows it is absolutely crucial to its street credibility that the new generation tyres are beyond reproach. In short, there can be no excuses.
During initial technical discussions between all teams, FIA, F1 and Pirelli it was agreed that tyre diameter would increase marginally, from 660mm to 720mm, with rims incorporating fixed wheel covers and finger recesses. The latter are intended to help mechanics carry the heavier wheels during pit stops. Covers displaying graphics were considered but pushed back, potentially to 2023.
Mario Isola, Pirelli’s head of car racing, says they requested information from teams on expected levels of downforce [and resultant g-forces], details on engine torque and power outputs and anticipated maximum speeds. Once the data had been verified – he smiles as he recalls “crazy figures” provided during a similar exercise in 2016 – Pirelli prepared the first finite element models to design ‘virtual’ 18-inch tyres.
“Heat transfer is an important parameter because the spacing between the brakes and the rim is much higher,” Isola explains. “Therefore we predict there will a lot less heat transfer from the brakes,” in turn affecting tyre warm-up.
“We supplied two different models for simulation purposes – a finite element model [FEM] and a thermal mechanical model of the tyre which is what teams use in their simulators, including driver-in-the-loop simulators.”
Pirelli’s FEM data is encrypted. “We are the owner of the model and only we know what’s inside, but we update it periodically depending on feedback we get from the teams. Sometimes you get feedback from teams that is quite different, so they adjust their simulations or we adjust our model depending on the situation.”
During the pandemic these techniques were adapted to enable Pirelli to remotely develop three different road car tyre ranges, all of which have since been launched.
“[F1] enabled us to develop new techniques,” says Pirelli’s research and development chief Pierangelo Misani. “If you need tyres that are light with less material than the standard one you have to reduce tolerances. So, I can say the experience [obtained] in Formula 1 is not purely related to materials, it is not purely related to geometry, it is not purely related to performance, but also to development tools and methods, and manufacturing processes.”
Misani adds that the [shape] of the tyre is fundamental. “It determines how the tyre will generate forces, because it’s how you put the contact patch on the ground and how the forces that are generated are transmitted to the rim, then to the car. The final profile is crucial to the process as it dictates the moulds that are required for batch production of the prototype tyres used for both laboratory and track testing.”
In other words, get it wrong and its back to square one, whereas materials used for actual carcass construction and compound ingredients can be fine-tuned later.
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“To validate the profile, we asked – and [FIA, F1 and the teams] agreed – to start testing in September 2019.” This was done with ‘mule’ cars, adapted from 2018 cars to replicate ride height, downforce and car mass. “That way we had the possibility to freeze the profile, then to start focusing on construction and compounds in 2020.”
All was running to schedule and four teams had completed ‘dry’ tests. Then Covid struck, which brought the process to an immediate and inconvenient halt for two months as all teams went on an FIA-enforced shutdown during April and May.
In the interim Pirelli continued its indoor test programme at its Milan R&D base using tyres produced in batches of 10 by its F1 plant in Slatina, Romania and trucked to Italy. (Pirelli has replicated its F1 production line at its Izmit, Turkey facility – per chance situated 20km from the site of last Sunday’s grand prix – lest the Romanian plant be hit by natural, or other, disasters.)
Once F1 was back on track, testing resumed with nine of the ten teams committing their participation. Williams declined as it was in the thick of its sale process to Dorilton Capital when agreement for this costly exercise was required.
Underlining the importance of the coming change, even world champion Lewis Hamilton, who usually shuns testing, offered his services at Imola after this year’s Emilia Romagna Grand Prix.
“I don’t ever volunteer for test days and it’s probably one of the first ones that I have volunteered for,” he said afterwards, adding with a smile, “So I immediately regretted it when I woke up in the morning on the day! I was like ‘damn it!’.
“It was at a really great track to test at so I enjoyed the day and the weather was good. I plan to be [in F1] next year and want to be a part of it, I want to help Pirelli towards having a better product.
“It’s important for me to gauge what the starting point is and what differences I can help with, so that from a driver point of view we have more mechanical grip from the tyres, less degradation. It was a good test, and obviously it was the first step of the tyres, but it definitely wasn’t a bad place to start.”
Isola says the tests provided “results that were coherent across different cars and across different circuits,” adding, “we had the possibility to validate different constructions starting from Jerez to Bahrain, Imola.”
All tests across Pirelli’s prototype dry, intermediate and wet tyre ranges have been completed aside from a final one-day ‘wet’ test at Paul Ricard with Alpine next Monday. As part of the programme all tyre-specific data was shared with teams, and updated on an as-and-when basis. All teams bar Williams – which did not build a ‘mule’ – will attend a composite two-day test in Abu Dhabi after this year’s finale.
“We’ve had feedback lap times and basic information from each test, with technical bulletins coming through from Pirelli,” confirms AlphaTauri technical director Jody Egginton. “We’ve done a lot of simulation work with the model [of] the tyre, so we understand what it’s going to do, we’ve got a good grip in vehicle dynamics terms.”
However, he makes a point about a hefty elephant lurking in a corner of the design office: “We’ve got a big increase in tyre and wheel mass, plus we’re not allowed to run (mass damping) inerters [from next year].”
Isola says car mass will increase by 14 kilograms due to the heavier wheel and rim assemblies, split roughly 3kg per front wheel and 4kg for rears. Simply put, there’s more heavier alloy metal and less lighter tyre rubber, hence an undesirable increase in un-sprung weight. Add in the fact sophisticated suspension systems are banned from 2022 and the extent of next year’s re-engineering challenge becomes clear.
Teams are by now in the thick of manufacturing their 2022 cars, having based their concepts on data obtained from wind tunnel studies, simulations and computational fluid dynamics calculations. Pirelli’s input, in particular tyre modelling data and 60% scale wind tunnel tyres, which accurately simulate tyre behaviour at speed, was crucial to this process.
The wind tunnel models, produced in a dedicated studio in Rome, are a major contributor as tyres constitute a third of frontal area while spinning at enormous speeds. The resultant wake affects airflow across the entire car, while steered wheels deform in compression, yaw, and pitch, causing sidewalls and contact patches to constantly change shape. An aerodynamicist’s nightmare, in other words, unless these mini-tyres are spot on.
For teams the biggest challenge is yet to come: translating tyre test data into on-track performance. Ferrari racing director Laurent Mekies says the 2022 F1 season brings “three massive pillars that are completely new: completely different aerodynamic regulations, different ways to operate the car (due to revised sporting regulations) and mechanical suspension, which nobody has had for 10 or 15 years.
“So a lot of different limitations. And in the middle of those, how to ‘switch on’ the completely new tyres. I think that’s going to be the big challenge. There will be a huge amount of discovery with the 18-inch [wheels]. It’s a great challenge as a team to make sure we have the base to get the core understanding we need.
“There will be a very steep learning curve, but in two years we will look back at the starting point and wonder what we were doing at the time…”
Mekies does not foresee the switch to 18-inch wheels alone as resulting in major changes to the competitive order but believes it will prove a contributory factor when taken in conjunction with the three ‘pillars’.
“I think it will be a combination of the concepts, the new regulations, how they interact with the tyres and how you make everything work. I think we have the potential to see a surprise also from midfield teams. It’s risk and opportunity for everybody.”
All parties agree that the level of research that has gone into the 2022 regulations by far exceeds what has gone before – whether at FIA, F1 or team levels – while Pirelli has been afforded longer development times than at any previous stage in its 10-year F1 history; indeed, longer than any tyre supplier has previously been afforded, with the pandemic further opening the window.
That is how crucial the bigger black roundels that adorn each corner of a 2022 grand prix car are to the future of the sport. Not only are they the single biggest visual indicator of F1’s ‘new era’, but the biggest single advance in F1 tyre technology since the sport adopted radial ply tyres in the seventies; possible even more so. Pirelli must not screw up, and Isola and his team knows it.
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