Overview
- Article C5.4.3 now requires compression‑ratio compliance checks at ambient temperature and 130°C from 1 June to 31 December 2026, moving to operating‑temperature checks only from 2027.
- The World Motor Sport Council ratified the amendment by unanimous e‑vote, with power‑unit manufacturers also backing key elements of the change.
- The FIA text bans any component or arrangement designed to increase compression ratio beyond 16.0 in operating conditions, and manufacturers must have their checking methods approved by the FIA.
- The start date was brought forward from an initial August plan to 1 June, a window that falls between the Canadian and Monaco Grands Prix and gives teams limited time to validate or adjust designs.
- Mercedes and its customers McLaren, Alpine and Williams must ensure compliance by June, as rivals report the suspected on‑track gain at roughly a dozen horsepower while Mercedes disputes any significant benefit; the FIA is also continuing technical evaluations on energy‑management rules after Barcelona and Bahrain testing.