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Mercedes’ rivals have succeeded in securing a rule change following a pre-season technical row over engine performance.<\/b><\/p>\n
Audi, Ferrari, Red Bull and Honda had been pushing for a change in the regulation governing compression ratios on the basis they believed Mercedes had secured an advantage through clever use of materials technology.<\/p>\n
Formula 1’s governing body the FIA said on Saturday that a change to the way the compression ratio was measured would be introduced on 1 June, with a further revision for the 2027 season.<\/p>\n
A statement said the rule change had been approved unanimously by all power-unit manufacturers.<\/p>\n
The compression ratio is a measurement of the cylinder displacement between the two extremes of the piston stroke. Typically, an increase will lead to more power.<\/p>\n
Some estimates of the gain Mercedes could be achieving have been as much as 0.3 seconds a lap, but Mercedes F1 boss Toto Wolff has said it amounts to “a few horsepower – in England you would say a couple, which is more like two and three”.<\/p>\n
The original rule stated the ratio would be limited to 16:1 in the new engine rules introduced this year – a change from 18:1 under the previous regulations – and this was measured at ambient temperature.<\/p>\n
Mercedes’ rivals were pushing for the compression ratio to be measured at operating temperature.<\/p>\n
The Mercedes engine has been measured by the FIA at both ambient and operating temperature and complied with the limit of 16:1 at all times, senior F1 insiders have told BBC Sport.<\/p>\n
Compression ratios tend to decrease as an engine rises in temperature because of thermal expansion of the materials involved. The belief was Mercedes had found a more effective way to limit this loss than other manufacturers.<\/p>\n
From 1 June, the compression ratio will be measured at 130C as well as ambient temperature, and from next year only at 130C.<\/p>\n
That means that from next year, manufacturers will be able to have engines that exceed a compression ratio of 16:1 at ambient temperature, even though this reduction from the previous limit was introduced into the 2026 regulations to make the rules more appealing to new manufacturers.<\/p>\n
Audi and Ford both entered F1 because they were attracted by the new power-unit rules, which introduce a near 50-50 split between internal combustion and electrical power, and Honda reversed a decision to quit.<\/p>\n
A statement from the FIA said: “A significant effort has been invested in finding a solution to the topic of compression ratio.<\/p>\n
“The regulations introduced for 2026 represent one of the biggest changes in recent memory.<\/p>\n
“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.<\/p>\n
“Further evaluation and technical checks on energy management matters are ongoing.”<\/p>\n
This last sentence is a reference to discussions over energy deployment and recovery.<\/p>\n