Why F1 teams will be looking to F2 to gain an edge in 2021

One of the few throwbacks left in Formula 1 is about to depart. Over the course of its history so far, manual gearboxes, naturally-aspirated engines and ground effects have come and gone from grand prix racing. Soon, another familiar element will also exit stage left and join those past pinnacles of technology on the sidelines.

Oxymoronically, one of F1's most high-profile changes that have been announced for 2021 so far is the introduction of low-profile Pirelli tyres. That year, the wheel rims will extend in diameter from 13 inches to 18, bringing the tyres far more in line with their contemporary road-going counterparts. But at the Spanish Grand Prix earlier this month, feeder category Formula 2 revealed that it would make the same switch a season prior.

On the face of it, it's a well-timed switch that makes sense; any rookie hopefuls aiming to make their F1 debut in 2021 will have had - assuming they've gone through the FIA's prescribed path that includes F2 - a year to train on Pirelli's new products, making them far more viable prospects as the F1 regulations get their presumed colossal overhaul.

Aside from the aesthetic impact, the main change that the low-profile tyres will bring to F1 has been underplayed somewhat - partly in deference to furthering the championship's target to completely shake up the formula for 2021, and partly because nobody really likes talking about tyres. Today's F1 cars are hugely sophisticated, teeming with technological triumphs both on and under the skin of the machines, but the biggest differentiator is how those advances can get the four big, round bodies of rubber to bite into the track without wearing out too much.

There's going to be plenty of difference in how the new tyres perform compared to the current 13-inch tyres. This is why in preparation for 2020, F2 is planning to roll out a number of changes to its Dallara chassis, which will then be starting its third year of service.

Once the cars have the requisite modifications, and Pirelli has a full 18-inch tyre ready to go, F2 will begin proper testing ahead of next season's festivities - although a preliminary shakedown took place at Mugello prior to the championship announcing the switch. It's a short timeframe but, as Pirelli motorsport chief Mario Isola explains, it's a plan that has been in the works since the season began.

"We started a discussion at the beginning of the year with the promoter to move F2 with 18 inches tyres," he says. "It's a big challenge, because we don't have a lot of time to make the new product, but luckily we had some information coming from 2014. If you remember, we ran a car in Monaco in '14 with 18-inch tyres [with Martin Brundle driving Dallara's GP2/11], and at the time there was a discussion [as to] whether F1 would plan to move to 18 inches.

"F2 wants to anticipate the trend that we have in F1 so we started the development of the 18-inch tyres, but then we stopped because F1 decided to go for the wider tyre, and F2 has not.

"Now, we have decided together to take the challenge to go to 18-inch tyres in 2020. The changes on the car are something that the promoter is evaluating - [but] for sure there will be a new suspension.

"I don't know if they want to modify anything else on the car, so they are obviously analysing the impact of the 18-inch tyre. We are developing a first prototype and giving them some data in terms of stiffness and so on, so they can start designing the new suspension."

The handling characteristics with the new tyres will be very different

Addressing any changes to the suspension geometry is the key area of importance, as the new tyre will introduce inherently different characteristics to the car, thanks to the larger rim and thinner sidewall. The wheel will also be slightly larger - Pirelli has confirmed that F2 will switch from the current 660mm diameter to 705mm - so the car will have to accommodate this change.

In short, a smaller sidewall results in a stiffer suspension set-up. The tyre essentially acts as a second spring in the suspension geometry, and the greater stiffness of the 18-inch tyre means that the teams will have to react differently when selecting spring and torsion bar settings for each race. A good chunk of the data painstakingly collected from each circuit over the years will therefore be rendered archaic, leaving the teams with more work to do to recover that information.

What's surprising is that the brakes on the F2 car won't be changed, and presumably the combination of Brembo calipers and Carbone Industrie discs and pads can be turned up enough to boost the stopping power of the F2 car, as the larger wheel diameters produce a greater level of inertia.

That's also in the interests of cost, as the changes to the suspension and the required new rims will add to the overheads of each F2 team. It's unknown whether any of those components will be partially subsidised to ease the financial pressures on each team, or whether there will be further changes to the bodywork to mitigate any aerodynamic effect. But seat prices will undoubtedly be adjusted to cover those initial costs.

With those larger diameter wheels, the pushrods will be replaced to maintain the ride height - although the other suspension members are expected to remain unchanged.

Furthermore, says Isola, the handling characteristics with the new tyres will change considerably. With the stiffer sidewall, the amount of flex in the tyre will be completely different, creating a more direct response to the drivers' inputs.

"It should be more reactive," he suggests, "more precise, especially the front. We need to consider the impact on kerbs, because an 18-inch tyre has less sidewall than a 13-inch tyre. It's a difference that we have to consider.

"The target is to have a performance that is in line with the current one, so obviously it will be a new product with a big margin of development compared to the 13-inch, but the first year the target is to be close to the current one."

With that reduced flex, the tyre will deform less on the road. When cornering, tyres produce something known as a slip angle, which is the difference between the angle of steering and the direction that the cars are physically heading in. Due to the larger flex at the contact patch in the current tyre, the slip angles are larger than what they will be - meaning that, on lower-profile tyres, that direction should be instantly more in line with the steering angle provided.

But the caveat of that is, with reduced deformation, a lower profile tyre can theoretically snap much sooner as it loses grip. While a 13-inch tyre has that delayed response to steering as a result of the increased slip angles, it can also flex more as the car teeters on the knife-edge of grip. Without that movement from the rubber, the drivers might find their way into a spin more often - so will have to adapt to the new tyres.

The reduced movement from the tyre would, ordinarily, also mean that it is more difficult to warm up as the elastomers expel less energy, but Isola is confident that Pirelli can sidestep that issue with clever compound design. F2 doesn't use tyre blankets - and in 2021, F1 will do away with them too, meaning that the onus is purely on the driver to generate the right amount of heat.

"I don't think [it will be harder to warm tyres]," he says. "It's all about the optimisation of the footprint, and how to design the compounds without blankets. We keep the same approach without blankets, but it's all about how we make the footprint work."

F2 driver Louis Deletraz suggests this could shake up the competitive order, and that much of the early advantage in 2020 will swing to those who can find the right tyre temperatures in their set-up as the teams begin to understand how the new design works.

"It will change a lot for the engineers in terms of set-up," says Deletraz. "Now, to be in the temperature range is critical. In quali, [if] we didn't get it quite right it can be half a second - or more - you lose. You set the whole car up to work for the tyre, so for sure everything will change."

Many of the changes being made to the F2 car are similar to what F1 will try with the trio of 'mule cars' provided by Mercedes, McLaren and Renault

Tyre wear is also another consideration. With F1's transition to thinner-gauge tyres for 2019, the amount of thermal degradation that resulted in tyre blistering has been reduced - but that's shifted the main wear mechanism to 'graining' on the tyre surface. Undoubtedly, with a stiffer tyre, that'll change once more.

"We have to evaluate the wear profile," explains Isola, "the level of wear, and evaluate the new compounds on what we see in the tests. Track testing will be very important for our development, we'll make a lot of calculations based on simulations and so on. That's why we are planning to have maybe eight to 10 sessions from now to the end of the year.

"We have to develop the wet tyre as well, it's another important product, and we have to collect all of this data: the running temperature, running pressure. Consider, for example, the running pressure - having a smaller volume of air, you can imagine we have a bigger delta pressure from cold to hot, and this has an influence on how the tyre works."

Once that's all done, Pirelli will have to rinse and repeat to develop the 2021 tyres for F1. With wider tyres to produce for the top level, there won't be too much carryover from the F2 specification, but the experience in building the 18-inch tyres will, suggests Isola, give the company's engineers more tools to get it right for F1.

"These are two cars with a - well, not completely different performance, but the level of performance with F1 cars is quite a step compared to F2," he says. "Especially in 2017 when they decided to increase the level of performance with the wider tyres [in F1].

"I believe the experience we will collect with Formula 2 will be important, because for one year we have F2 racing with 18-inch tyres, and you know that the race environment is different compared to testing. With all the cars on track, we can evaluate how the rubber stays on track or not. When you test with only one car it is impossible to evaluate that."

Many of the changes being made to the F2 car are similar to what F1 will try with the trio of 'mule cars' provided by Mercedes, McLaren and Renault. New F1 suspension members are needed in reaction to the larger wheel diameter - but there's also a projected change in the aerodynamics in anticipation of the 2021 regulations.

"We are not planning to have new brakes," Isola explains, "because we don't have enough time, and also the regulations are not defined yet - so on the current 2019 cars it's [about] modifying the suspension and taking off a little bit of downforce, because with the expected regulation for '21 the cars should have less downforce."

Not only does bringing F2 into the fold for larger diameter wheel rims help the drivers to acclimatise ahead of a prospective promotion to F1, but it also gives Pirelli a year under its belt to work on a project that produces a similar family of tyres.

From the F1 teams' perspectives, the move to 18-inch tyres is just one of many changes mooted to come in for 2021 that they must consider. With the pecking order stale and the interest in yet more years of Mercedes domination waning, a complete rethink of tyre profile isn't the most glamorous of changes the series could make.

But decades of experience on a 13-inch tyre are about to go out of the window and, depending on who can get to grips with that first, that could be vital.