Mercedes arrived at the Canadian Grand Prix earlier this season with its first major upgrade package, which included revisions to the front wing and floor of the W17.
Among the most eye-catching elements were several additions to the upper section of the diffuser, featuring spike-like serrated profiles stretching across more than half of its width.
The purpose of those profiles was to effectively extend the diffuser and enhance its aerodynamic effect, a concept that drew immediate attention from rival teams in the paddock.
Ferrari was among the first to raise concerns, asking the FIA for clarification on whether it would be permitted to develop a similar design for its own car.
The Scuderia did not receive the green light to pursue that avenue, reflecting the FIA’s growing unease about where such development could lead.
The governing body issued a technical directive following the Barcelona Grand Prix, a document now referred to as an FIA doc, which comes into force from the Austrian Grand Prix weekend onwards.
The FIA’s primary concern was that the Mercedes solution could open the door to increasingly creative interpretations of the rules that the governing body would not be comfortable with going forward.
Mercedes has acknowledged that minor tweaks to the diffuser were required in line with the new guidelines, with those changes already visible during media day in Austria.
The diffuser extensions remain on the W17 to a certain extent, but the distinctive spike-like profile that defined the Montreal-spec design has been removed entirely.
Racing Bulls has also been asked to modify its own diffuser extensions, confirming that Mercedes was not the only team caught in the scope of the new directive.
Teams throughout the paddock have confirmed that room still exists to explore diffuser development in a less extreme fashion, meaning the concept has not been shut down entirely.
Ferrari’s SF-26 has been seen running its own diffuser extensions, while customer team Haas runs a similar concept using multiple elements on its challenger.
Those solutions, like Mercedes’ revised Austria-spec diffuser, fall within the boundaries of what is currently permitted under the new FIA guidelines.
The development race in this area reflects how important the diffuser has become in the current generation of cars, which rely less on ground effect than their predecessors.
Since winter testing, teams across the grid have been searching for inventive ways to extend diffuser performance, including adding extensions directly to the rear crash structure.