How Pirelli is testing 2026 F1 tyres without 2026 cars

Pirelli has entered the next stage of preparing its smaller tyres for the 2026 Formula 1 season, with Ferrari and McLaren testing its harder compounds in Barcelona this week.

A lot of attention has gone to Lewis Hamilton continuing his preparations with his new Italian employer alongside team-mate Charles Leclerc and McLaren’s Lando Norris, but it cannot be stressed enough that lap times from the two-day test at the Circuit de Barcelona-Catalunya are entirely meaningless – heavily depending on the run programmes requested by Pirelli to test its smaller prototype tyres for 2026 and its compounds at the harder end of the scale.

While Hamilton will have benefited from more seat time in a Ferrari from last year, with the latest procedures, steering wheel, Ferrari power unit and so on, the biggest benefactor from the test is Pirelli itself. The Italian tyre manufacturer is up against it to test and produce tyres that are narrower – 25mm at the front and 30mm at the rear – and smaller in diameter, from 720mm to 705mm-710mm front to rear, to be used on vastly different cars next year.

The difficulty for Pirelli is that it has no representative cars to test its new rubber on as the 2026 cars feature significantly reduced drag and less downforce generated by the floor and diffuser.

Initial plans to reduce overall downforce by 40 percent have been watered down to around 15 percent following concerns over slower lap times, which are now expected to be more in line with current performance levels. But the new generation of cars are substantially different in how and where they generate performance, so Pirelli has to rely on the imperfect solution of mule cars – machinery from 2022-2024 with trimmed wings – to collect real-life data from its new rubber.

Following an initial test with Aston Martin in September – in its 2022 model – and recent wet-compound running at Le Castellet, Ferrari and McLaren conducted work in Barcelona in more recent cars with significantly lower wing levels, appearing with fully flat mainplanes more akin to something one would see in Baku or Las Vegas rather than at the high-downforce Montmelo circuit.

Charles Leclerc, Ferrari SF-24 during Pirelli test

Photo by: Pirelli

The overall downforce levels of these mule cars will be relatively close to the start-of-2026 specifications, but because the cars are so different it is still difficult for Pirelli to correctly reproduce the loads its tyres will be subjected to. It is therefore relying on being regularly fed simulations from teams to stay ahead of the curve.

“The first tests were mainly dedicated to understand how the mule cars are working, because obviously they are different,” Pirelli’s motorsport chief Mario Isola told Autosport. “The only thing we can do is to continuously ask for updated 2026 simulations from the teams, basically. We must update our know-how and update our construction according to the data that we receive.

“We cannot just rely on the mule cars because it won’t be sensible, and we will continue to provide them a virtual model of the tyre to use in their simulators and they come back to us with their feedback. And this is the right direction we should continue in.”

Both reducing downforce overall and changing how it is generated will have a major impact on the nature of the loads 2026’s smaller tyres are going to be subjected to. For Pirelli it is therefore crucial to get the internal construction of its new tyres in the right ballpark. Any further fine-tuning can then be done through tweaking the compounds.

The Italians are not just taking expected 2026 performance into account, as F1 squads always tend to find rapid gains at the start of a regulations cycle, and Pirelli therefore has to have enough headroom to account for higher tyre loads further down the line.

One important challenge added to the mix is the upcoming X-mode, a DRS-like form of active aerodynamics which changes the angle of the front and rear wings on the straights for higher top speeds, as opposed to the standard configuration which is dubbed Z-mode.

“We cannot generate these downforce levels with the X-mode and Z-mode, it’s impossible,” Isola explained. “So, we have to understand what the best compromise for testing is and when we try to correlate the data from simulations with data collected on track. The first step is to define the profile and construction. From the test we had with Aston Martin we have a good starting point, I would say. Compound development is the second step.

Mario Isola, Racing Manager, Pirelli Motorsport

Photo by: Mark Sutton / Motorsport Images

“We know that it’s a challenge, because in any case teams don’t want to lose any performance compared to the current cars, and the tyres are smaller, with lower loading capacity and so on. We are also again testing new materials and new ideas in order to have a tyre that is not heavier but still able to sustain the load and to keep the same performance that the current tyres have.”

It is not the first time Pirelli has been chasing a moving target with one hand tied behind its back. But Isola pointed out the challenge for 2026 was perhaps slightly easier than in 2017, when F1 moved to bigger and wider cars with much more downforce, which at the time was impossible to replicate with a mule car. F1’s move to ground-effect based cars for 2022 was also a challenging proposition.

“This is a very similar situation to what we had for 2017 and 2022 when we had to develop a complete new tyre for a complete new car, so it’s not something new to us,” Isola said in an earlier roundtable.

“In 2016 it was super difficult because it was expected to have cars with much higher downforce and the performance was five or six seconds quicker than the previous year, so it was impossible to replicate this kind of performance.

“But the way you achieve the load with the current cars is completely different compared to the new one, for example. And on the straights, we have a lot of load now, while in 2026 at high speed we should have less load. So, the comparison is not the same.”