Formula 1’s manufacturers have agreed to revised compression ratio rules in a move that could help Mercedes’ rivals make up lost ground next year.
The new test for hot conditions will now come into force much sooner than expected, and there is new tighter wording in the regulations designed to prevent tricks that could get around the test.
Mercedes has been at the centre of a controversy over the winter after it emerged that it had found a way to exploit a new 16:1 compression ratio limit that had been imposed for 2026.
With the rules stating checks would take place in ambient conditions, it had found a way to increase its compression ratio – which delivers more performance – when the engine was up at hot operating temperatures.
Rivals had pushed for a change to the procedures to stamp out its advantage, and an original suggestion had been for a new hot test to be added alongside the cold test to be introduced from August 1.
But with such a route not being ideal for manufacturers to work out how best to exploit the situation for themselves, further discussions took place about an alternative solution.
Now, following a vote of F1’s Power Unit Advisory Committee (PUAC), it has been agreed that the new hot test – which will take place when components have been warmed to 130C – will come into force six races earlier than originally planned.
A statement from the FIA said that a lot of work had gone into reaching an agreement on the compression ratio issue – which it said had been backed unanimously.
“A significant effort has been invested in finding a solution to the topic of the compression ratio,” the FIA said.
“This parameter, which was one of the key fundamental targets of these regulations in order to attract newcomers to the sport, is limited in the regulations to 16:1, measured in cold conditions.
“The FIA has worked to find a compromise solution which determines that the compression ratio will be controlled in both hot and cold conditions from 1 June 2026, and subsequently only in the operating conditions (130deg C) from 2027 onwards.”
The June 1 date falls between the Canadian and Monaco GPs, rounds seven and eight, meaning any competitive form reset triggered by the change – if Mercedes has to make any alterations to its design – will happen two months earlier than was originally suggested.
However, Mercedes has been adamant it will have no problem passing the additional test and that it will make no difference to its form. This may well explain why it did not vote against the change of regulation.
The FIA's new rules from June 1 also rule out any trick designs that aim to exploit the compression ratio situation.
Updated regulations state: "Any component, assembly, mechanism, or integrated arrangement of components that is designed or functions to increase the compression ratio in operating conditions beyond 16.0 is prohibited."
Of more importance to Mercedes’ rivals is the removal of the cold test for 2027 – which means that compression ratios will only be checked when hot.
With power units typically reducing their compression ratio when they get hotter, it means that only needing to pass the hot test will be a boost to Mercedes’ competitors when it comes to designing a power unit that exploits this area of performance.
They have been scratching their heads about how Mercedes has managed to design internal components that increase, rather than decrease, the compression ratio when the power unit gets hot.
With both a cold test and a hot test in place to check on the 16:1 limit, that made it much harder for Mercedes’ rivals to design engines that could get close to a higher limit as they would already be losing ground when things moved from cold to hot.
Now, with just a hot test, it means they have more leeway to target a higher compression ratio overall.
While Mercedes’ rivals have been adamant that the potential gain on offer from the compression ratio trick is as much as 13bhp - which can be worth 0.3–0.4 seconds per lap – Mercedes disagrees.
Team boss Toto Wolff said the gains had been blown out of proportion as he reckoned it was only worth a couple of horsepower at best.
In another smaller regulation update, the eight minute gap between Q2 and Q3 has been reduced to seven but Q3 itself has been extended from 12 minutes to 13.
