Mercedes has agreed to close an engine loophole that rivals believe could be worth several tenths of a second, but the rule change won’t come into effect until 1 June.

Tweaks to the qualifying format have also been approved for 2026, but the more contentious matters of engine management and the start procedure remain unchanged.

Teams have suspected that Mercedes is exploiting a loophole in the regulations to run its engine with an increased compression ratio to boost power.

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The compression ratio is the difference in cylinder volume when the cylinder head is at its highest point relative to its lowest point. It was reduced from 18:1 under the previous rules to 16:1 from this season.

But the regulations also stipulated that the compression ratio would be measured at ambient temperature. Rumours suggest that Mercedes has found a way to increase the compression ratio when the engine was at operating temperature.

Mercedes denied it had found any significant advantage, with team boss Toto Wolff describing the compression ratio trick being worth a low single-digit boost to horsepower, though Max Verstappen said Red Bull Racing believes it could be worth 10 times as much.

Rival manufacturers started the year determined to have the loophole closed, and with governing body the FIA preferring not to have the season start under the cloud of technical controversy, the regulations have been changed just days out from the first race.

The new regulation requires the compression ratio be measured at both ambient temperature and at 130°C.

However, because of the long lead time on engine development, the rule change will be delayed until 1 June, between the Canadian and Monaco grands prix, the seventh and eighth rounds of the season — though this is sooner than what had appeared to be the initial plan for a change during the August mid-season break.

Engine designs had to be locked in for the season on Sunday, 1 March, but the regulations allow dispensation for modification in the event of a rule change like this.

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The rule change passed unanimously, meaning all five engine manufacturers, including Mercedes, agreed to the new wording expressly banning tricks that increase the compression ratio.

Mercedes voting against its own technical interests would appear to corroborate Wolff’s assertion that the trick was worth relatively little power and that ensuring compliance would be no big deal.

However, requiring compression ratio to be validated at both ambient and running temperature appears to be a win for the German marque, given speculation rival manufacturers had been hoping to exploit the rules to their own benefit.

Compression ratio naturally decreases as temperature increases — which is why the Mercedes trick to boost it when running hot attracted so much interest.

If the rule had been changed to measure the engine only at 130°C and not at ambient temperature as well, some believe Mercedes’s rivals intended to build in a higher cold compression ratio to ensure the engine was at exactly 16:1 when running hot. That will not be possible with the double measurement.

The 2027 regulations, however, will measure the compression ratio only at operating temperature.

“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 (130°C) from 2027 onwards.

“The regulations introduced for 2026 represent one of the biggest changes in recent memory. All parties acknowledge that with the introduction of such significant regulatory changes, there are collective learnings to be taken from pre-season testing and the initial rounds of the 2026 championship.”

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QUALIFYING CHANGES

Qualifying will look slightly different from this weekend’s Australian Grand Prix, with the pole-setting Q3 session running slightly longer this year.

Q1, Q2 and Q3 have typically run for 18, 15 and 12 minutes each.

This year Q3 will last an extra minute, with the break preceding shortened by a minute to keep the overall running time unchanged.

Despite the session still comprising only 10 cars, the extra minute will allow teams and drivers more flexibility to prepare for their usual two bids for pole position.

Flying lap preparation is likely to look different this season given the conflicting requirements to both keep the battery as close to full as possible and also push hard enough to get the tyres up to temperature. Depending on the circuit, some teams will prefer to undertake two preparation laps to balance those demands.

Because the grid has expanded to 22 cars this year, the rules have also been tweaked to confirm that six cars, up from five, will be eliminated from qualifying in both Q1 and Q2, leaving 10 to compete for pole position in the longer Q3.

A further tweak has been made regarding active bodywork — the movable front and rear wings than change position depending on whether the car is on a straight or in the corners.

Race control can force drivers to remain in cornering mode in low-grip conditions or for any other reason.

The qualifying rules stipulate that straight mode can only be re-enabled if five minutes or more remain in qualifying, ensuring every driver will have a chance to set a time with the movable bodywork active.

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MONACO TYRE RULE HEADLINES OTHER CHANGES

The special rule mandating two tyre changes in dry weather for the Monaco Grand Prix has been scrapped after last year’s trial.

Drivers were forced to use at least three tyre sets at last year’s race in a bid to spice up the action, but the grand prix descended into farce, with teammates lapping extremely slowly to hold up the field and held the sister car make their extra pit stop without losing positions.

With the rule having had no discernible impact on overtaking and with drivers and team bosses speaking out strongly against the rule in the aftermath, the regulation has been dropped.

The rule requiring drivers to wear cool suits during races declared a heat hazard has also been dropped. Some drivers had hit out at making the system mandatory, particularly given some had found the suit and ancillary parts uncomfortable in the tight cockpit confines.

Every car, however, will have to carry the system when a heat hazard is declared, ensuring no weight disadvantage for those drivers who choose to use it.

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MATTERS LEFT UNRESOLVED

The FIA statement noted that “further evaluation and technical checks on energy management matters are ongoing”, ensuring it remains a major talking point ahead of Melbourne.

McLaren principal Andrea Stella raised safety concerns about some of the measures required for driver to regenerate electrical energy from lap to lap in Bahrain. Lifting and coasting is a regular part of driving the modern Formula 1 car to keep the battery topped up, leading to sometimes considerable speed differences at the end of the straights.

This is expected to be more severe in Melbourne, which is tipped to be one of the hardest tracks for the battery.

Several possible solutions have been floated and were trialled during the final three days of testing in Bahrain.

One of them was to allow the battery to steal more energy from the internal combustion engine. Charging from ‘super clipping’ is limited to 250 kilowatts, but the hybrid motor is capable of charging at up to 350 kilowatts. While boosting the super clipping limit would slow the cars more through certain corners, it would mean drivers could lift and coast less aggressively.

Another alternative is to reduce the amount of power output from the hybrid motor from its currently mandated maximum of 350 kilowatts, ensuring the battery drains less quickly, though this would slow the cars down the straights.

The matter, however, is deeply contentious given some manufacturers feel their power units are more efficient than others and therefore see rule changes in this space as detrimental to their own potential advantage.

The same applies to the regulations regarding races starts.

Stella suggested the increased risk of drivers stalling on the grid or getting otherwise poor getaways could lead to dangerous start-line crashes.

This is because the new power unit is difficult to get off the line.

Whereas drivers had pretty much instant access to full power under the previous rules because part of the hybrid system kept the turbo spooled up automatically, this year the process is far more manual.

Drivers must spool up the turbocharger by keeping the revs high for around 10 seconds on the grid, and electrical energy can be deployed only when above 50 kilometres per hour.

Ferrari, however, has designed its power unit to be more responsive off the line and has been opposed to changes that would neuter that advantage, especially as reports suggest team boss Fred Vasseur raised it as a potential issue many months ago but was shut down.

The rules currently stipulate that “once all the F1 cars have come to a halt, the first red light will be illuminated” — in other words, the starting procedure gets underway immediately. The five lights come on at one-second intervals, and all give are extinguished after a random hold time.

Drivers at the back, therefore, wouldn’t have 10 seconds to prepare for the race start.

During testing, the FIA trialled a procedure whereby drivers were given a five-second warning before the red lights came on, effectively giving them their 10-second window to prepare the turbo.

That rule hasn’t made it into the rule book, though there could be scope for the race director to implement it anyway on safety grounds.

The same applies to a likely ban on activating the straight-line mode of the active aerodynamics at the start. Though not stipulated in the regulations, there is scope for the race director to issue directives that would prevent drivers from switching to low-downforce mode off the line.