Mercedes’ rivals have succeeded in forcing a rule change following a pre-season technical dispute over engine performance.
Audi, Ferrari, Red Bull, and Honda were pushing for a change to the regulations governing compression ratios on the grounds that they believed Mercedes had gained an advantage through the clever use of material technology.
Formula 1’s governing body, the FIA, said on Saturday that changes to the way compression ratios are measured will be introduced on June 1, with a further amendment for the 2027 season.
All power-unit manufacturers have unanimously approved the rule change, the FIA said in a statement.
Compression ratio is a measure of cylinder displacement between the two extremes of the piston stroke. Typically, growth will result in more power.
Some estimates suggest Mercedes may have an advantage of 0.3 seconds per lap, but Mercedes F1 boss Toto Wolff has said the number is “equivalent to a few horsepower – in England you would say ‘a couple’, which is the same as ‘two’ and ‘three’.”
New engine rules were introduced this year.
The original rule stated that the new engine rules introduced this year would limit the ratio to 16:1 – a change from 18:1 under the previous rules – and it was measured at ambient temperatures.
Mercedes’ rivals were insisting on measuring the compression ratio at operating temperature.
The Mercedes engine has been measured by the FIA at both ambient and operating temperatures and complied with the 16:1 limit at all times, senior F1 insiders have told BBC Sport.
The compression ratio decreases as the temperature increases due to thermal expansion of the materials involved in the engine. The belief was that Mercedes had found a more effective way of limiting this loss than other manufacturers.
From June 1, the compression ratio will be measured at 130°C along with ambient temperature, and from next year onwards it will be measured only at 130°C.
This means that from next year, manufacturers will be able to have engines with a compression ratio greater than 16:1 at ambient temperatures, even though this reduction from the previous limit was introduced in the 2026 rules to make the rules more attractive to new manufacturers.
Audi and Ford both entered F1 because they were attracted by the new power-unit rules, which introduced a roughly 50-50 split between internal combustion and electric power, and Honda reversed the decision to leave.
The FIA said in a statement that they have made a significant effort to find a solution to the issue of compression ratio.
“The rules introduced for 2026 represent one of the biggest changes in recent memory.
“All parties acknowledge that with the introduction of such significant regulatory changes, collective lessons must be learned from pre-season testing and the early stages of the 2026 Championship.
“Further assessment and technical investigation on energy management matters is ongoing.”
This last sentence is a reference to the discussion on energy deployment and recovery.
Drivers have complained that energy-draining cars have led to unusual and counterproductive driving techniques – and there have been several proposals to change the rules to make energy management easier.
