Mercedes’ rivals have managed to change the rules after a pre-season technical row over engine performance issues.
Audi, Ferrari, Red Bull and Honda have been pushing for changes to compression ratio regulations because they believe Mercedes has gained an advantage through clever use of materials technology.
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Formula One’s governing body, the FIA, said on Saturday it would change the way compression ratio is measured on June 1, with further revisions for the 2027 season.
A statement said the rule changes had been unanimously approved by all power unit manufacturers.
Compression ratio is a measurement of cylinder displacement between the two extremes of the piston stroke. Usually, with increases comes more power.
Some estimates put the gain Mercedes could achieve as high as 0.3 seconds per lap, but Mercedes F1 boss Toto Wolff said it would be equivalent to “a few horsepower – in England you would say a few horsepower, it’s more like two and three horsepower”.
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The original rule stated that in the new engine rules introduced this year, the ratio would be limited to 16:1 – the ratio in the previous rule was 18:1 – and this was measured at ambient temperature.
Mercedes’ rivals are pushing to measure compression ratio at operating temperature.
Senior F1 insiders told BBC Sport that the FIA ​​measured the Mercedes engine at ambient and operating temperatures and it always complied with the 16:1 limit.
Compression ratio tends to decrease as engine temperature increases due to thermal expansion of the materials involved. Mercedes is believed to have found more effective ways than other manufacturers to limit this damage.
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From June 1, the compression ratio will be measured at 130°C and ambient temperature, and from next year only at 130°C.
This means that from next year, manufacturers will be able to produce engines with compression ratios in excess of 16:1 at ambient temperatures, although reductions from the previous limit are being introduced in the 2026 regulations to make the rules more attractive to new manufacturers.
Audi and Ford both joined F1 as they were attracted by new power unit rules that introduced an almost 50:50 split between combustion engines and electric power, while Honda reversed its decision to withdraw.
A statement from the FIA ​​said: “We put a lot of effort into finding a solution to the compression ratio issue.
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“The regulations introduced in 2026 are one of the biggest changes in recent years.
“All parties acknowledge that with such significant regulatory changes on the horizon, there is collective experience to be learned from pre-season testing and the opening round of the 2026 Championship.
“Further assessment and technical inspection of energy management issues is ongoing.”
The last sentence quotes a discussion about energy deployment and recycling.
Drivers complain that the lack of energy in their cars results in unusual and counter-intuitive driving techniques – and there are various proposals to change the rules to make energy management easier.
