FIA Sets Hot-Test Method; Commission Vote to Decide

Rival manufacturers raised alarms about a perceived loophole in the new 16:1 compression-ratio limit after reports suggested Mercedes — and to a lesser extent Red Bull — had found a way to pass ambient, stationary FIA checks while running an effectively higher compression on track. Industry estimates put the potential benefit at roughly 10–15 bhp (commonly expressed as about 0.3–0.4 seconds per lap), and observers warned that customer teams using Mercedes power units — McLaren, Williams and Alpine — could also gain.

Ferrari, Audi and Honda formally pressed the FIA for clarity. Audi’s F1 project chief Mattia Binotto urged a measurement method that captures operating (hot) conditions and warned against filing protests without clear evidence, while Audi technical director James Key called for decisive action to preserve the rules’ intent. Red Bull Powertrains (RBPT) described its unit’s compliance as, in RBPT technical director Ben Hodgkinson’s words, “crystal clear” and downplayed the controversy. The dispute focused on whether rule C5.4.3 — which defines compression under ambient conditions — could be exploited through thermal expansion during the engine’s working cycle.

Teams discussed responses ranging from formal protests to attempts to replicate the approach under the 2026 in-season development framework. The FIA convened engine technical experts and manufacturer representatives earlier this week to resolve the interpretation.

Attendees agreed a technical route to measure compression ratios at operating (hot) temperatures, creating a clear path to close the perceived loophole. However, ambient-temperature measurements remain the official standard for now; any formal change to testing or enforcement will require consultation with manufacturer principals and a vote in the F1 Commission. That Commission includes several Mercedes-powered teams and two Red Bull squads, so immediate implementation for the 2026 season was not expected.

The meeting established a future measurement methodology and clarified enforcement intentions, but the timing and adoption of a hot-temperature testing regime for 2026 remain uncertain. Teams will watch the consultation and Commission process closely for any binding change.