Mercedes compression ratio ‘loophole’ closes ahead of Monaco Grand Prix

Mercedes have won all five Formula 1 races so far this season, but the Brackley-based team could be about to lose part of their advantage.

This weekend’s Monaco Grand Prix - the first of nine successive events in Europe - will bring an end to a possible ‘loophole’ Mercedes have been accused of utilising.

Mercedes' British driver George Russell races during the 2026 Formula 1 Grand Prix du Canada at Circuit Gilles-Villeneuve in Montreal, Canada, on May 24, 2026. (Photo by ANDREJ IVANOV / AFP)

placeholder image — Mercedes' British driver George Russell races during the 2026 Formula 1 Grand Prix du Canada at Circuit Gilles-Villeneuve in Montreal, Canada, on May 24, 2026. (Photo by ANDREJ IVANOV / AFP)

Under the new F1 regulations for 2026, the FIA reduced the engine compression ratio to 16:1, however Mercedes were accused by rivals of running a higher ratio than the ruleset intended.

With measurements only taken when the engine was cold and static in the pitlane, Mercedes had been suspected of mimicking a higher compression ratio while out on track.

It was believed that heat-expanding metals in Mercedes’ engine were able to create the conditions for the old 18:1 ratio.

This may have resulted in a small performance gain for the Silver Arrows through more efficient combustion. Some rivals believed the effect could have been worth several horsepower.

From Monaco onwards, however, the FIA will measure compression ratios at an engine temperature of 130°C, closing the potential loophole.

There may not be such a noticeable difference around the streets of Monte Carlo, considering it is both the shortest and slowest track of the season.

But it is likely a subtle difference will be felt, benefiting Mercedes’ nearest challengers in the constructors’ championship: Ferrari and McLaren.

At first glance, the change may appear unlikely to affect McLaren given they also use Mercedes power units. But the reigning champions may not have known how to exploit such a loophole.

Regardless of the way compression ratios are measured, Mercedes were always expected to take a brief backward step in Monaco due to Ferrari and McLaren being superior in slow-speed corners.

This could make life more difficult for Italian championship leader Kimi Antonelli, who arrives in Monaco on a four-race winning streak.

It also doesn’t make good reading for nearest challenger and Mercedes teammate George Russell, who is eager to bounce back from his enforced retirement in Canada.

The Monaco Grand Prix gets underway at 2pm UK time this Sunday (June 7).