F1 2026: FIA announce compression ratio decision after Mercedes engine controversy

A decision has been announced by the FIA regarding the geometric compression ratio controversy, ahead of the 2026 F1 season.

F1's governing body have made a change to their technical regulations just a week out from the start of F1's new era at the season-opening Australian Grand Prix, after a vote between the five power unit manufacturers.

2026 is seeing a raft of regulation changes sweeping into F1, including on the power unit side of things, where there is a greater emphasis on electrical energy as well as an internal combustion engine that can run off 100 per cent sustainable fuels.

And amid these power unit rule changes, Mercedes managed to come up with a clever trick within their power unit design which Max Verstappen believed was worth between 20-30 brake horsepower, or 0.3 seconds per lap.

The clever trick meant that the geometric compression ratio within the power unit could be at the allowed 16:1 when the car was stationary, but then increase to the previously allowed 18:1 when moving, with the previous FIA regulations stating this would only be measured when the car was stationary and at an ambient temperature.

However, the FIA announced earlier this month that there would be a vote between the five power unit manufacturers on the grid in 2026 on whether the rules should be changed to mean that the compression ratio was measured at both ambient and operational temperatures.

The vote only needed a 4-1 majority, and the FIA have now been revealed the change has officially passed, with F1's governing body releasing a revised technical regulations document ahead of the season-opening Australian GP next weekend.

Rules now state that before May 31, geometric compression ratios will only be measured at ambient temperatures, but from June 1, 2026, they will also be measured when the engine is at 130 degrees Celsius.

This means that Mercedes will not need to change their power unit design immediately, but will need to have got rid of that clever trick from the Monaco GP onwards.

F1 Engine Compression Ratio: What is it and why is it so controversial?

Mercedes dominance off the table?

For much of the winter off-season, Mercedes have been thought to be the favourites to claim both championship titles in 2026, with the power unit quirk one of the reasons given for their predicted superiority over the rest of the field.

But the last few weeks have suggested they are not going to have it all their own way. Ferrari looked supremely quick during Bahrain pre-season testing, while Red Bull and McLaren will also likely be in the mix at certain race weekends.

This new ruling means any advantage Mercedes and their power unit customers may have had in the early season will likely take a hit from the eighth race weekend of onwards, a further blow considering the previous proposal suggested that the change to the compression ratio measurement only come in from August 1.

Honda, Red Bull, Ferrari, Audi and Mercedes are the five power unit manufacturers in the sport this year, and together they passed the vote which will also see geometric compression ratios measured only at operational temperatures from the 2027 season, a further revision to the mid-season rule change for 2026.

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