The Compression
Ratio Controversy
Why a single measurement temperature is at the centre of an F1 regulatory debate — and what the FIA is doing to clarify the rules.
New to this topic?
Start with the first section below — it explains compression ratio in plain English before diving into the controversy.
How It Unfolded
FIA adds "ambient temperature" measurement clause to compression ratio rule — opens a grey area.
Rumours emerge that Mercedes (and possibly Red Bull) have designed engines to exploit thermal expansion.
FIA begins discussions with Power Unit Advisory Committee. Ferrari, Honda, Alpine and Red Bull push for a rule change.
FIA launches formal e-vote: should the ratio be tested at 130°C operating temperature from 1 August 2026?
E-vote deadline — one day before engine homologation freeze on 1 March.
Proposed date for new hot-temperature measurement test to come into effect (if vote passes).
Frequently Asked Questions
This page will be updated as the e-vote result and further developments emerge. Last updated: February 2026.