FIA rule change introduced at F1 Monaco Grand Prix 'to close Mercedes loophole'

Toto Wolff in Zandvoort — Photo: © IMAGO

Monaco Grand Prix

FIA rule change introduced 'to close Mercedes loophole' after F1 domination

The rule change becomes active on June 1

Graham Shaw Consultant Editor

Digital sports specialist running global brands for 30 years

Friday 29 May 2026 17:57

A key FIA rule change will become active for the first time at the Monaco Grand Prix and it could have major implications for the Mercedes domination in 2026.

The new rule concerns the measurement of engine compression ratios, and it officially comes into play on June 1, just in time for race weekend in the principality.

From that date F1 power units will face stricter checks which are designed to close a loophole which meany experts believe has given all-conquering Mercedes an edge so far this season. The team has won all five races so far and dominates the early standings.

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Why the FIA acted over 'Mercedes loophole'

Controversy had been mounting over the winter when whispers of the loophole - allegedly exploited by the Silver Arrows - became the subject of heated debate.

This season the maximum compression ratio has been reduced from 18:1 to 16:1 with many observers suspecting that top teams might have been using innovative materials to skirt around this limit.

Previously, measurements were taken on cold, static engines, meaning that thermal expansion during a race could significantly boost the actual compression ratio.

Now though, following successful lobbying by Audi, Honda, and Ferrari, the sport’s governing body has agreed to supplement the traditional cold engine test with one conducted at 130°C. Although this change was initially slated for August, it has now been brought forward to June 1.

Wolff and Verstappen at odds over potential advantage

Some estimates suggest the situation up to now may have shaved roughly three-tenths of a second off each lap, though Mercedes team principal Toto Wolff insists the real benefit amounts to only two or three horsepower. During winter tests Max Verstappen argued that they should effectively be zero.

Verstappen was vocal about the 'Mercedes loophole'

Wolff has been emphatic in brushing aside the controversy, saying: "If those numbers were true, I understand the concerns, but ultimately it isn’t worth fighting over. It makes no difference for us whether we continue as before or adopt the new regulations."

He stressed that Mercedes prefers to cooperate rather than engage in a dispute over such a marginal gain.

Will new rule impact F1 pecking order in 2026?

Among Mercedes’ rivals, there remains some doubt as to whether closing this loophole will truly dent their dominant run. Ferrari team principal Fred Vasseur says: "I’m not convinced that the new compression ratio rule will be a game changer."

Only time will tell if testing engines at 130°C will have an immediate effect on the race order. The upcoming Monaco weekend will serve as the first true test, even if the circuit is widely regarded as one of the least sensitive to power differences.

F1 Mercedes Toto Wolff Monaco Grand Prix