Formula 1's governing body, the FIA, has approved unanimous changes to how engine compression ratios are measured in the 2026 power units, effective from 1 June. The decision addresses concerns raised by manufacturers including Audi, Ferrari, and Honda over Mercedes' compliance during hot operating conditions. The revisions aim to ensure fairness while maintaining the 16:1 limit introduced to attract newcomers to the sport.
The compression ratio, which measures the compression of the air-fuel mixture in a cylinder, was reduced to 16:1 for the 2026 Formula 1 regulations from the previous 18:1 limit. This change was intended to make engine development more accessible for newcomers like Audi and compatible with fully sustainable fuels.
Controversy arose when rivals discovered that Mercedes' engines complied with the 16:1 ratio at ambient temperatures during static tests but appeared to achieve a higher ratio when running hot, potentially due to material expansion in components like pistons and connecting rods. Audi, joined by Ferrari and Honda, sent a joint letter to the FIA, arguing under Article 1.5 that engines must comply with regulations at all times during competition.
FIA single-seater director Nikolas Tombazis explained the need for clarity: “There are a lot of nuances when discussing such a matter, because there's what the regulations intend to be, and to keep the compression ratio at 16:1 was one of the core objectives when the regulations were discussed with the PU manufacturers back in 2022.” The governing body initially saw no issue after a 22 January technical meeting but later recognized ambiguities in the wording.
The compromise, approved by all five power unit manufacturers—Mercedes, Ferrari, Honda, Audi, and Red Bull-Ford—introduces dual measurements: ambient temperature until 31 May 2026, then both ambient and 130°C from 1 June to year-end. From 2027, only hot conditions at 130°C will apply. Revised Article C5.4.3 prohibits any designs that increase the ratio beyond 16:1 in operating conditions.
Mercedes team principal Toto Wolff described the outcome as “a fair game for everyone,” noting it prevents rivals from exploiting opposite advantages. He called the debate “a storm in a teacup,” estimating any gain at just a few horsepower. Red Bull's Laurent Mekies emphasized the need for clarity: “We’re asking for clarity. Tell us what we’re allowed to do, and the rest matters little.”
The FIA stated that significant effort went into the solution, which was ratified by the World Motor Sport Council. It also noted ongoing evaluations of energy management from pre-season testing and early races, given the major regulatory shifts for 2026. Tombazis downplayed the issue's scale: “People get a bit too excited, and I don't think this topic ever needed to get to this level of attention.” The changes come ahead of the season opener in Melbourne next week.
