Formula 1's five power unit manufacturers are set to vote on a proposed change to how engine compression ratios are measured, which could come into force over the summer break. The 2026 power unit regulations prescribe an engine compression ratio of 16:1, down from 18:1 last year. That compression ratio has always been measured at ambient temperature when the engine isn't running, so it doesn't account for any material expansion under heat when cars are running out on track.

A group of rival manufacturers, understood to be led by Audi, have been worried about Mercedes coming up with a trick to increase the compression ratio closer to 18:1 when the car is actually running while still complying with the static test, which some OEMs are worried could bake in a significant horsepower advantage. One compromise would be to introduce additional tests over the summer break or ahead of the 2027 season instead, with the former solution now the subject of a vote, proposing an additional mandatory test at 130 degrees to be introduced from 1 August 2026.

The mechanism to do so is a vote through the relevant Power Unit Advisory Committee. As well as Mercedes, Ferrari, Audi, Red Bull Ford and Honda, the FIA and commercial rights holder FOM will also vote on the matter, requiring a supermajority of four manufacturers plus the two bodies for the change to be voted through. The FIA had been keen to draw a line under the matter as soon as possible, so F1 2026's first technical controversy wouldn't spill out into the start of the season next month in Australia.