Why F1's 18-inch tyre conundrum is not straightforward

As Formula 1 continues to debate exactly what direction it should take in 2021, one piece of the puzzle fell into place last week - but only due to a legal scheduling obligation that required the FIA to draw a line in the sand and get on with it.

The 2020-2023 sole supplier tyre tender had to be issued this month to allow potential candidates the opportunity to bid against Pirelli. That meant finalising the tyre specifications for the new era, which begins from the second of those four seasons.

We now know that in 2021, F1 will make the momentous move from 13-inch to 18-inch wheel rims, finally bringing it in line with where the motor industry has been going for decades. In addition, front tyres will be 35mm narrower, and diameters will rise from the current 670mm to the 700-720mm range. And, after years of debate on the matter, tyre warmers will not be permitted.

The move to a low tyre profile is also perhaps the first hint that the new generation of F1 cars will to some degree be 'styled' by the new regulations, in much the same way as the new Formula E car. So, what else does the tender reveal, and what does it all mean?

The first thing to know is that the 'Invitation to Tender' is exactly that - newcomers have the same chance as Pirelli to win the deal. The process involves both the FIA and F1, and there's a delicate political balance, with the latter making the real call, but the former ensuring that it is seen formally agreeing to it.

The first step is that candidates must prove to the FIA that they can meet the detailed technical and safety requirements outlined in the tender, at which point they become 'Approved Bidders'.

Those names are then submitted to the commercial rights holder, in other words Liberty, which then discusses the money side - how much each company is willing to pay to be the F1's official tyre partner. That is linked to areas such as signage around the circuits, and potentially, title sponsorship of individual races.

F1 then submits its final choice to the FIA, which then formally appoints the winner. The chosen company will then sign contracts with the FIA, F1 and each of the teams.

You don't have to be a genius to work out that if more than one manufacturer gains FIA approval, it will come down to money, and how much Liberty can squeeze out of each candidate. There's no doubt that in the past the always loyal Bernie Ecclestone had a soft spot for Pirelli, and its charismatic boss Marco Tronchetti Provera, and that gave the Italian company an edge in negotiations. Now all bets are off - it will be purely about the numbers.

The question is - who other than Pirelli will enter the contest by the August 31 submission deadline?

Michelin is top of the list of likely candidates to bid against Pirelli

Certainly, Michelin, which made it clear last time around that it wanted a move to a modern low profile format for marketing reasons, is top of the list of likely candidates. It is associated with many FIA championships, including FE, and enjoys a friendly relationship with Jean Todt and the governing body - indeed the French company is also a 'global partner' of the FIA Action for Road Safety campaign, and the FIA prizegiving event.

There are others competing at high levels of motorsport who could throw their hats into the ring, and who may well have much bigger marketing budgets than Pirelli can stretch to. The PR downside for all contenders is that there is much less space for their logos on 18-inch tyres...

There is also another obvious complication for any new entrant. By a quirk of timing this latest four-year cycle starts one year before the big technical changes coming for 2021, of which the 18in rims are the first confirmed element.

And that means that 2020 will be run with the current wheel size. So, any newcomer must develop 'normal' tyres for just one season, while at the same time preparing for the momentous move for the following year. That's a huge ask, and quite possibly a deal breaker for some companies considering a bid.

This anomaly was very obvious to the FIA, and indeed consideration was given to bridging the gap by extending Pirelli's current deal by a year, and starting the new contract period in 2021 with a clean break from the old sizes.

But that would be a legal minefield, given how precise the FIA tender process is. And for Pirelli it would be like turkeys voting for Christmas - why take that extra year only to make it easier for someone else to come in and steal your place in 2021? Unsurprisingly, Pirelli had no interest in taking that route.

"There was a discussion about that," says F1 race director Charlie Whiting. "That's why the tyre tender is for four years, so there'll be three years with the likely new sizes in '21, '22 and '23. It would probably have been quite elegant if we'd been able to extend the existing contract, but that wasn't possible. It was a discussion between our legal department and the legal department of our current supplier."

The glass half full approach for any new supplier is that a year with old sizes - getting to know F1 and the teams while quietly developing the more complex 18-inch product in the background - might actually be an easier way to start than arriving in 2021 amid a hurricane of other technical and commercial changes.

As the incumbent, with what will be nine years of continuous experience by the time the new contract period starts, Pirelli clearly has a huge advantage.

But the company points out that even with current sizes the interim season will not be so straightforward. It has to create new tyres every year to deal with increasing downforce levels, and this time will also have to meet other demands set out in the tender such as increased degradation levels and bigger performance gaps between the compounds.

"We have to design a new tyre anyway," says Pirelli F1 boss Mario Isola. "So it's not an advantage or disadvantage for anybody. When you are in F1 you have to design a new tyre every year. If you don't change anything in the regulations, the development of the car is changing the stress you put on the tyre. We are in F1 since 2011, and we never had one year where we kept the same product.

"OK, the change in size is a much bigger step compared to changing the compounds, or whatever. But in F1 you must consider that you have to develop a new product every year. And ideally also during the year, but the regulations say that we have to freeze the product, because you should follow the development of the car."

Over the last couple of seasons Pirelli has been asked by the FIA to make tyres that match the requirements set out in a so-called 'target letter'. But that document carried no formal weight. Now, for the first time, a detailed target letter has been incorporated into the tender itself, and as such it becomes part of the contractual obligations of the supplier.

The intention of the parameters set out in that letter is to create better racing, with more pitstops. The tender explains: "The intent is to create the maximum number of race strategies yielding race times such that multi-stop strategies provide just enough potential of a beneficial outcome to encourage the greatest variety in the racing spectacle." And as noted that starts from 2020, not just '21 with the new sizes.

"With these new numbers you have a two-stop or a three-stop, that gives you a bigger advantage, compared to one stop" Mario Isola

"They ask for more degradation, they ask for a bigger delta lap time between compounds," says Isola. "If these are the targets for 2020, because the targets are not considering the change of size, we need to develop a new product, if we are selected, considering the numbers.

"They calculated different numbers also with experience from this year and last year, because we know that if the current target letter was defined considering one-stop, two-stop and three-stop, with very similar race time within five seconds. We know now that all the teams are moving towards one-stop, because it's less risky.

"I think with these new numbers you have a two-stop or a three-stop - that gives you a bigger advantage, compared to one-stop."

Adjusting to the required degradation levels with the current sizes in 2020 is just the first step. The move from 13-inch to 18-inch for '21 is going to be a massive technical challenge, combined with the narrower fronts - a tweak understood to be part of the aero changes aimed at helping cars to follow each other. Add in the ban on tyre warmers and you can see that whichever company gets the gig will have a lot to deal with.

Many racing categories run without tyre blankets - including Formula 2, which is supplied by Pirelli - but the superior performance level and higher loadings associated with F1 will make it that much more difficult.

"It's important that we make an analysis to understand what is the pressure evolution," says Isola. "Because with the new rules, tyres are starting cold and then you go up to 120-130C, so the delta temperature is a lot bigger, and the delta pressure is a lot bigger.

"You cannot start at 5psi cold, because the performance of the car is from lap one, so it's important to have a minimum cold pressure that is enough for the car in the first couple of laps, then you increase the pressure and increase the temperature.

"It's important to understand how the tyres are working during this temperature and pressure evolution, and when they stabilise. It's not very easy to make a tyre like that. We make tyres for F2, they start cold, but the performance of F2 is not the performance of F1. Now we have more than 12 seconds as an average lap time difference. It's a huge difference."

And Isola adds that the pressure change has a significant impact on tyre behaviour.

"Consider that now with the blankets the pressure evolution during a run is a few psi," he says. "We are talking about 2-3psi, from cold to running, cool-down lap, the variation in pressure is very, very limited.

"With the new tyres [there will be] a big variation in pressure, which means you have a big variation in profile and footprint. So, it's probably more difficult to achieve the targets in any conditions, because we are running in 21 different circuits, with different cars. We always make a plan or development considering the average, but the average is not really representative of everybody."

So, it's a huge task for the supplier, but also for the F1 teams, who will have a raft of other major changes to deal with in 2021. But it's not just a question of the general characteristics of the tyres, such as degradation, that are outlined in the target letter, or the fact that narrower fronts will have an obvious impact on balance.

The move to low profile tyres, with far less compliance than the current rubber, has major implications for the whole suspension system. It's not yet clear to what degree teams will be allowed to use the extra five inches of space within the wheels for brakes and associated cooling and aerodynamic parts, but clearly there's the possibility of major changes happening in those areas.

There's also a massive aerodynamic impact generated by tyres being 30-50mm taller than the current product, with fronts that are 35mm narrower. All of that must be taken into consideration in the windtunnel long before anyone drives a 2021 car on track.

Despite the huge impact it will have on them, most of the detail in the FIA tender request came as a surprise to the teams

That in turn feeds off the 60% scale windtunnel tyres that the winning bidder has to produce well in advance. Ensuring that they behave exactly like the real thing has never been the work of a moment, although in theory a low-profile tunnel tyre should be easier to deal with, and keep its shape better. That might improve correlation - and ultimately help all teams.

Not that they've had much chance to do the sums yet. One of the most extraordinary aspects of last week's tender announcement was there wasn't one - it crept unheralded onto the FIA website, and teams were alerted to its existence by the media some hours later.

Despite the huge impact it will have on them, most of the detail also came as a surprise to the teams - although they knew that the 18-inch change was on the table. And as far as the FIA and F1 are concerned, it's a done deal, and teams won't be able to lobby for any adjustments.

If only the rest of the 2021 changes could be achieved so painlessly...