In the Mercedes camp, the issue does not seem related to material expansion, but rather a geometric solution that passes FIA cold checks while potentially violating Article 1.5 of the Technical Regulations, which requires cars to comply at all times during an event. Will Brixworth redesign the piston crown or challenge the FIA?
The regulatory clarification request reportedly came from three manufacturers—Honda, Ferrari, and Audi—who wrote to the FIA to determine whether Mercedes’ 2026 engine combustion chamber design is legal. The engine, when hot, could achieve an 18:1 compression ratio, while under the new cold regulations, it is limited to 16:1.
Mercedes has remained silent for now, confident that their solution complies with FIA cold checks. However, rivals contest that it violates Article 1.5, which specifies that cars must conform throughout the entire race weekend. Critics argue the design is not in the spirit of the regulations.
The protest could have erupted at the Australian GP, the first race of the new era of agile cars, potentially preventing four teams—Mercedes, McLaren, Williams, and Alpine—from racing if a non-compliance was found.
Starting a new regulatory cycle with a major controversy would not have been ideal, especially since the changes are already complex for fans to understand. Early confusion among spectators was likely to be inevitable.
The issue surfaced before the Christmas break, giving Mercedes time to find a solution. Sources suggest the piston crown could be redesigned by one or two tenths of a millimeter to achieve the required combustion chamber volume at operating temperature. This would result in a slight power loss, though not the 15-horsepower drop reported by German site Motorsport Magazine.
The contested solution has apparently been known for months, as all manufacturers have seen engineer movements. About sixty engineers left Brixworth, the Mercedes engine hub, to join Red Bull Powertrains in Milton Keynes, while others moved to Honda, Audi, and Ferrari. RBP benefited from technical insights from Brackley, applying the Mercedes six-cylinder concept to their own engine.
There was no spy scandal. Claims that a break-in at Renault Sport’s Viry-Châtillon site aimed to steal Mercedes engine data intended for Alpine are false. Despite mandatory “gardening periods,” F1 has always allowed free circulation of ideas. Knowing what rivals do does not mean being able to replicate their solutions at the same pace.
Recently, discussions have focused on metal expansion and new materials to increase compression ratios, but all F1 manufacturers are already familiar with these techniques. The real debate lies elsewhere.
Now the matter is with FIA technical delegate Jo Bauer and his team. According to Corriere dello Sport, a compromise may be sought to “save face” for all parties:
Under this potential deal, Mercedes (and Red Bull Powertrains) would slightly reduce their “cold” compression ratio to ensure they stay within legal limits when the engine is running hot. Unless Mercedes chooses to dig in for a brutal legal battle, this compromise appears the most likely path forward. To do otherwise would set a dangerous precedent, inviting every other manufacturer to push their own solutions beyond the legal limit and inviting endless litigation.
Ultimately, the FIA is seeking a compromise to resolve a technical dispute over Mercedes’ 2026 combustion chamber geometry, which rivals claim bypasses compression limits when hot. By pushing for a slight “cold” ratio reduction, the governing body hopes to avoid a disqualification crisis at the Australian Grand Prix and prevent a precedent that could lead to widespread regulatory evasion.
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