Mark Hughes: Advantage Mercedes? Behind the F1 rumours for 2026

It’s unusual that a technical controversy should arise in Formula 1 before the concept has even been raced but that’s what happened during the off-season with the revelation that Mercedes had found a way to circumnavigate the 2026 regulation regarding the compression ratio of the new power units.

The regulation states a maximum compression ratio of 16:1, as measured in ambient temperatures and (obviously) when not running. Mercedes, it’s believed, has found a way to increase the length of the conrod when the engine is running, to such an extent it can achieve a compression ratio more like 18:1 (which, incidentally, was the previous limit).

Red Bull Powertrains has recruited quite heavily from Mercedes’ High Performance Powertrains organisation in Brixworth and it seems that’s how the information leaked. Red Bull Powertrains duly set about incorporating the feature into its own new engine, though it’s at a less-advanced state of development and seemingly has not yet seen the same gains, which if achieved are in the order of 10-15bhp and worth around 0.3sec of lap time.

Ferrari, Audi and Honda, upon hearing this, sent a letter of objection to the FIA, pointing out that in addition to the technical regulations stating that the compression ratio is measured statically and at ambient temperatures, there is a cover-all part of the regulations stating that cars should comply with the regulations in all operating conditions. The FIA gave its opinion that if it cannot measure the compression ratio when running (which it cannot), then there is no evidence of illegality and that therefore the Mercedes interpretation is effectively legal. Even if it is anecdotally known that it exceeds the limit in reality.

This has been likened to the 2019 Ferrari fuel flow controversy, whereby the fuel flow limit was believed to be breached (as revealed by a former member of the team who had been recruited elsewhere) but there was no way of measuring if it had and no direct evidence. But in order to exploit the greater power of the illegally high fuel flow, Ferrari needed – at some tracks – to exceed the 100kg fuel capacity limit.

At the final 2019 race in Abu Dhabi, Ferrari was found to have miscalibrated its fuel measurement so that an indicated 100kg was found – when tested by the correctly calibrated FIA equipment – to be significantly in excess of that. So although it was impossible to prove that the fuel flow limit was being exceeded in operation, there was the smoking gun of the miscalibrated measurement equipment for the capacity.

There would only be disadvantage to running beyond 100kg (more car weight) unless of course it was allowing you to use more power through an illegally high fuel flow. The measured fuel in Charles Leclerc’s car before the start of the race was 4.88kg greater than declared or permitted. So there was evidence of both the technique used to misdeclare and the actual misdeclaration – which heavily supported the fuel flow breach theory. Because the fuel flow cheat required the blatant misdeclaration of the fuel capacity, it was quite a crude cheat.

In the case of the Mercedes compression ratio, there is no smoking gun. Only the (almost certainly accurate) hearsay. So it is not quite the same. It’s much more like the flexi-wings which pass the regulations at the stipulated static test but which exceed that flex at the higher loads seen on the track – something which every single team takes advantage of. In fact, it’s even better concealed than that – because the wing-flex is visually revealed (but not in a way which allows accurate measurement) by on-board cameras whereas the compression ratio cannot be.

The difference, of course, is that with flexi-wings, all the teams do it and therefore there is no competitive advantage for something which the FIA cannot definitively measure. With the compression ratio ruse, it’s become an issue because one (possibly two) engine manufacturers has it while the others have not worked out how to do it.

Lengthening the conrod through heat expansion is one thing. Using that to increase the compression ratio is quite another because typically, although the conrod will expand with heat, so does everything around it. The difference between the conrod heat expansion and that of the block invariably means you actually lose compression as the engine heats up. With the 2022-25 power units, the 18:1 compression reduced to around 17.2:1 at operating temperature. Manufacturers running their ’26 engines on the dyno report that the new regulation 16:1 compression ratio reduces to around 15.4:1 in operation. Yet Mercedes has apparently found a way to actually increase it.

“A meeting between the FIA and the engine makers was scheduled”

Although at the time of writing a meeting between the FIA and the engine manufacturers was scheduled to discuss the issue further, there is no expectation of a declaration of non-compliance for Mercedes. It’s more to discuss ways in which the compression ratio with the engine operating might be measured – with a view to further clarification for ’27.

Thus, Mercedes has potentially given itself and its three customer teams (McLaren, Alpine and Williams) a 0.3sec head-start for ’26. There is a tool the FIA can use to offset this: the new ADUO (Additional Development and Upgrade Opportunities) system. This allows any manufacturers found to be struggling after six races more funding, dyno time and potentially even new homologation of specifications. But how effective that might be we cannot know.

Expansion and contraction. Of the metal and in the principle; the boffins expand the possibilities, the regulators contract their space in which to do it. So the game of Formula 1 continues.

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