The FIA has confirmed a mid-season rule change to close a loophole in Formula 1's engine compression ratio regulations, following a dispute involving Mercedes. The new test, effective from June 1, will measure the compression ratio at an engine ambient temperature of 130 degrees Celsius, addressing concerns that Mercedes had been exploiting cold-temperature measurements.
The compression ratio limit has been reduced from 18.0 to 16.0 as part of F1's major regulation changes for 2026. Rival teams alleged that Mercedes found a way to circumvent the limit by taking advantage of the current test, which is only conducted when the engine is not at full operating temperature.
All five engine manufacturers—Mercedes, Ferrari, Red Bull-Ford, Audi, and Honda—unanimously approved 'some aspects of the amendments', according to the FIA. The governing body stated that the modifications follow pre-season tests in Barcelona and Bahrain, as well as extensive feedback from drivers and teams.
The FIA said: 'A significant effort has been invested in finding a solution to the topic of the compression ratio. This parameter, which was one of the key fundamental targets of these regulations in order to attract newcomers to the sport, is limited in the regulations to 16:1, measured in cold conditions.'
Mercedes team principal Toto Wolff initially suggested a rule change could be 'quite damaging for the performance', but later shifted his position, insisting Mercedes would be 'pretty comfortable' if challenged. He described the controversy as 'a storm in a teacup' and said the change 'doesn't change anything for us'.
The new rule will apply after the first seven races of the season, giving teams time to adjust. The FIA added that further evaluation and technical checks on energy management matters are ongoing.
