Formula 1 manufacturers have approved changes to the engine testing rules for 2026 following the compression ratio row that has lasted through the offseason.
In December, it emerged that Mercedes had found a possible loophole in the rules that could lead to a performance advantage with F1’s all-new engines for this season.
Rivals raised concerns that Mercedes had found a way to exceed the permitted compression ratio limit of 16:1 — which defines how much fuel can be squeeze into the engine before it ignites — when the engine was operational, while still complying with the rules as measurements are only taken when the engine is cold.
Although Red Bull/Ford was also believed to have found the same advantage, it united with Ferrari, Audi and Honda to try and get the rules changed before the new season.
The story dominated much of the car launch and preseason testing period, leading to multiple talks between F1’s engine manufacturers, F1 itself and the sport’s governing body, the FIA, to find a solution, especially given the threat of protests against cars in Australia if serious concerns lingered.
In Bahrain last week, the FIA announced a vote would take place on the potential introduction of both hot and cold testing of the engines from Aug. 1.
But after further talks about the new tests, the FIA announced on Saturday that the manufacturers had unanimously approved a “compromise solution” to test the compression ratios.
Both hot and cold testing will be introduced from June 1 this year, but from 2027, the compression ratios will only be measured in operating conditions, or 130ºC.
“The regulations introduced for 2026 represent one of the biggest changes in recent memory,” said an FIA spokesperson in a statement.
“All parties acknowledge that with the introduction of such significant regulatory changes, there are collective learnings to be taken from pre-season testing and the initial rounds of the 2026 championship.”
The spokesperson also said that “further evaluation and technical checks on energy management matters are ongoing” after some drivers and teams raised concerns through testing about the battery charging demands of F1’s new cars, and the possible impact on racing.
F1 CEO Stefano Domenicali urged patience with the new rules when speaking in Bahrain, expressing confidence the racing product would still be exciting, but he said the sport would not hesitate to intervene if action was required.
An end to an overblown row
As finicky and technical as the topic of compression ratios may be to the casual F1 fan, the furore surrounding their policing in the last two months has been a perfect example of F1 politicking.
In short, some teams feared that Mercedes had found an advantage, so wanted the rules to be changed. Mercedes had always been clear it was doing nothing wrong and that its engine was legal, passing all the required tests as well as getting clarification and feedback from the FIA.
Toto Wolff, the Mercedes team principal, suggested the possible advantage was only worth a few horsepower — not the few tenths of a second some rivals had feared — and that other teams were potentially looking for excuses before the season had even started.
Come Bahrain, the matter showed signs of petering out. Wolff suggested in a news conference at the second test that by testing the engine when it was both hot and cold, no manufacturers would be at an advantage, and that the rivals were seeking to only have hot testing.
The FIA’s technical chief, Nikolas Tombazis, told reporters in Bahrain that the matter never needed to get so blown out of proportion given the small performance benefits. “I’m not saying it’s not important,” he said. “But does it merit all this excitement for many months? Frankly, no.”
With the unanimous approval of the new testing that has now been written into F1’s rules, the compression ratio wrangling can finally be put to an end just in time before the season starts in Australia.