Pirelli's C6 experiment didn't work - but nor have the other 2025 F1 tyre trials

In its definition of its 2026 Formula 1 tyre compounds, Pirelli has admitted to something that had become patently obvious: the C6 experiment simply hasn't worked. The Italian rubber enthusiasts had issued a communique on Monday that stated it will homologate just five dry compounds for next season's all-new formula, taking us back to the C1-C5 range that we'd had in 2024.

A C6 compound had been developed and tested, but Pirelli was unable to produce a tyre with enough of a difference to the C5. This was one of the snippets of feedback that the brand had received about this year's C6; admittedly, feedback was hardly in scarce supply in the four weekends where the C6 appeared on the menu. Max Verstappen was one of the more vocal dissidents in Azerbaijan, suggesting that Pirelli would have been better off "leaving it at home" and, as it happened, it was not brought to any further races.

Thus, the news will be of some satisfaction to Verstappen - and to the other drivers who agreed with the four-time champion's point of view. The C6 was fundamentally flawed: unstable around a full qualifying lap, but without enough of a 'delta' to the C5 to justify the fragility of the compound. It was small wonder, then, that many chose to experiment with the 'medium' C5 in qualifying to find a more consistent lap. Of course, allocations didn't make that entirely possible; since the rule permitting free choice of tyre compounds was deleted in 2020, teams get just three sets of mediums per weekend. If teams were free to pick, one imagines the C6 wouldn't have been a particularly popular compound.

You can't criticise Pirelli for trying something different, particularly when it comes to the notion of widening the strategic options available for certain circuits. The constructions are so well-defined today that it's very easy to one-stop, worlds away from the camembert masquerading as tyres circa 2012-13. Sure, it would be nice to have scenarios at circuits like Monaco or Imola where there are options beyond stopping once and holding onto track position, but it's not a particularly realistic endeavour.

The C6 could work, if it could either a) last a little bit longer, or b) be redesigned to offer much more grip versus the C5 to make it worthwhile. Otherwise, it just feels like an unnecessary option that restricts the teams to two compounds for the race.

Bottas tests Pirelli's prototype tyres in Mexico - a range that the C6 will not be part of

Photo by: Pirelli

The problem is that, in this writer's opinion, none of the other tyre experiments have worked this year either. The mandatory two-stop in Monaco did nothing but force teams to use one driver to hold the pack up to allow the 'lead' driver to stop freely, and the allocation splits (i.e. missing out a tyre in the sequence, per Belgium's C1-C3-C4 allocation) simply dissuaded teams from ever using the hard compound.

In Mexico, for example, where the C2 operated as the hard compound versus the C4-C5 medium-soft duo, only Alex Albon and Franco Colapinto took the tyre through a meaningful stint. Colapinto's opinion was that the hard was a "very slow" tyre, and it appeared barely necessary given that others one-stopped with careful use of the C4 and C5.

Like the C6 compound, the tyre-split experiment could work with some fettling, but it might need another rule to make the most of it: make all three compounds mandatory.

With narrower tyres in 2026, the effect of thermal degradation might be more pronounced, and might even prompt teams to skirt the one-stop, two-stop border with greater regularity

The two-compound rule was introduced in 2007, intended to fill some of the void left by the disappearance of a tyre war when Michelin departed, and mandated at the time that everyone must use the prime (hard) tyre and the option (soft) tyre when Bridgestone brought only two compounds to a race. Ever since F1 had added a third compound to races in 2016, as Pirelli's confusing naming system made it possible that a supersoft, ultrasoft, and hypersoft could be given as the allocation, the idea of three mandatory compounds has been quietly mooted.

Yet, it has never reached mainstream support. In Brazil, following F1 Commission discussions over a potential plan to mandate two-stops, Racing Bulls team principal Alan Permane made his concerns over the idea known.

"Everyone likes two stops or more, but we have to be careful," Permane explained. "One of the things that makes a two-stop race tricky is when the tyres aren’t really suited for two stops. So you need to have tyres that demand the two-stop race. If you force a two-stop, you can end up with everyone doing the same strategy and actually have the opposite effect.

Permane didn't like the forced two-stop idea - but what if you made all three tyre compounds mandatory?

Photo by: Rudy Carezzevoli / Getty Images

"And don't forget, we've seen plenty of races with one guy on a one-stop and one guy on a two-stop, and then the guy on a one-stop being chased down by the two-stop – but that will obviously disappear. So I think we need to think very carefully. And we are. And I'm sure the F1 Commission will debate it, and I'm sure we'll come to the right answer."

The main variable here is not only degradation, but tyre performance - and this is where the allocation split could theoretically work. If, say, a race has a C1-C3-C4 allocation, with all three tyres being a mandatory option, then much of the strategy hinges on what a car can actually do with the C1. If a car can get the hard tyre to work, then it's a viable option; if it's a car like the Ferrari, where it can often struggle to build tyre temperature, then it might be advisable to short-stint it and play with the C3 and C4. The risk then is, if you short-stop on the hard, then you might need a third stop if a driver struggles to maintain tyre life on the C3 or C4 stint.

Maybe, if Pirelli is feeling a little bolder, then a double-split can be introduced. A C1-C3-C5 allocation could be an intriguing option for some of the mid-wear circuits like Silverstone or Sao Paulo, where the middle batch of compounds are employed. In that mould, Pirelli would then have a reason to revisit the C6 construction for a softer version of the double-split allocation; a C2-C4-C6 line-up for a circuit like Montreal could be an enthralling prospect.

We'll have to wait a little bit to see how the 2026 range of compounds stack up. With narrower tyres (25mm narrower at the front, 30mm at the rear), the effect of thermal degradation might be more pronounced, and might even prompt teams to skirt the one-stop, two-stop border with greater regularity. But if the range of compounds produce a strategic status quo, leading to an almost unilateral series of one-stop races, I might feel more comfortable bringing my more outlandish ideas to Mario Isola's attention.

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