FIA CLOSES MERCEDES LOOPHOLE / ANTONELLI THREATENED AT MONACO?

To understand what we are talking about, we need to go back to the basics of thermodynamics. An engine's compression ratio is the ratio between the cylinder volume with the piston at the bottom of its stroke and at the top. The higher the ratio, the more powerful the engine. The FIA set the limit at 16:1 for 2026, compared with 18:1 under the old regulations, notably to attract new engine manufacturers and make the formula more accessible.

The problem: the regulations stated that this value had to be measured "at ambient temperature", meaning with the engine cold and stationary. But metals expand with heat. According to rivals' suspicions, Mercedes designed an engine architecture that cleverly exploits the properties of its materials to stay under 16:1 during cold checks, while reaching a noticeably higher ratio once the engine is at its real operating temperature.

Put simply: the Mercedes engine was legal when cold. But nobody knew what it became when hot. And that is precisely the grey area the new rule now closes.

What makes this situation even more explosive is that Mercedes' supposed advantage does not only concern the Brackley team. Alpine, Williams and McLaren also use the Mercedes engine in 2026. If the thermal loophole really did deliver a power gain since the start of the season, these three teams have also benefited from it without knowing, or perhaps knowing full well.

This raises an immediate question: was McLaren's edge over Ferrari and Red Bull at the start of the season partly due to an illicit engine advantage? And what will happen in the coming weeks if Mercedes has to adapt its architecture?

Mercedes says it has nothing to change

Mercedes' official position is clear: according to the German manufacturer, no work on the engine will be needed to comply with the new rules. Something impossible to verify from the outside, which the paddock therefore greets with marked scepticism. Other sources believe Mercedes will have to modify the cylinder head, perhaps by adjusting the volume of the combustion chamber. A change that would take time and cost resources under the budget cap.

The irony of the situation is that Monaco is precisely the circuit least sensitive to engine power on the entire calendar. The streets of Monte-Carlo, with their slow corners, short straights and heavy braking zones, reward aerodynamics, mechanical balance and driver skill far more than an engine's extra horsepower.

In concrete terms: if Mercedes loses a few horsepower in Monaco, the impact on the race result will probably be minimal. The circuits where the effect will be most visible are: Barcelona (fast straights), Silverstone, Monza. That is where the real verdict will be delivered.

• Monaco (June 7): Estimated impact very low. The circuit is too slow for engine power to be decisive. Leclerc remains the favourite from pole.
• Barcelona (June 14): First real test of the impact. A long pit straight and several fast corners where power counts.
• Silverstone (July): The high-speed circuit par excellence. If Mercedes has lost power, it will be measurable here.
• Monza (September): The temple of speed. The final verdict on how much of an advantage Mercedes has lost.

The question is inevitable and it will fuel debate until the end of the season. Did Kimi Antonelli's four consecutive wins since Melbourne rest partly on an engine advantage that should never have existed? The honest answer is: nobody really knows. The FIA itself has never officially quantified the gain linked to the thermal loophole, assuming it really exists.

Nikolas Tombazis, the FIA's single-seater director, had even said during the off-season that he did not think the subject deserved "such a level of attention". That did not stop the federation from changing the regulations two months earlier than planned.

What is certain: if the loophole had no impact, the FIA would not have brought its entry into force forward by two months. The fact that five engine manufacturers voted unanimously to change the regulations is a strong signal in itself. You do not change a rule in a hurry if the problem is cosmetic.