Mercedes has appeared with a revised diffuser design at Formula 1's Austrian Grand Prix after a new FIA ruling effectively banned a trick it has employed for the last three races.

The move comes off the back of intrigue that has bubbled away ever since the design first appeared at the Canadian GP, with title rival Ferrari particularly agitated by this.

The Mercedes concept, which was also adopted by Racing Bulls and Haas, involved a clever way to effectively extend the length of the diffuser through the use of serrated wedges along the trailing edge.

While these extra diffuser extensions were quite small, they in theory provided a double benefit of increasing the efficiency of the diffuser for added downforce, as well as helping to better feed airflow to the rear wing.

While the laptime benefit from these diffuser extensions was not a game-changer, F1 teams know that every marginal gain is important for its overall performance.

Ferrari frustrations

Ferrari was especially upset about the Mercedes design because it had proposed to the FIA a similar - although not identical - concept four months ago that it hoped to be able to introduce for the start of the 2026 campaign.

Ferrari's idea was rejected by the governing body, though, so it abandoned any further work in this area.

So when the Mercedes version appeared in Montreal, Ferrari immediately sought clarification from the FIA. It is also understood that Red Bull joined in with complaints over the matter.

The Race has learned that, while Mercedes made some revisions to the design for Monaco in the wake of the discussions between rivals and the FIA, the matter came to a head in recent days off the back of a warning about the door being open to more extreme solutions if the Mercedes idea was not outlawed.

It was this which triggered the FIA to update a technical directive after the recent Barcelona GP that effectively stamped out the trick.

An edge radius trick

While bodywork in this diffuser area of the car is tightly governed by legality box restrictions, The Race has learned how the extra aerodynamic appendages were initially allowed.

This was through using a combination of other regulations that do allow extra design freedoms in this area of the car.

The first is the allowance for floor stays to be used by teams to stop bodywork flexing at high load.

As can be seen in the Mercedes design that appeared at Barcelona when viewed from above, the two serrated extensions are linked to two metal floor stays ahead of them.

Having the floor stays there opened the door to make use of an allowance in the regulations - through Article C3.2.6 - to fit what are known as "edge" and "fillet" radii to smooth out unwanted sharp edges.

Using these at trailing edges opens up the ability to fill in discontinuities, meaning teams can fit small closed fairings.

These must blend tangentially with the filleted surfaces and fit within what is known as an acute circular cone (as can be seen in the Mercedes design).

There are strict dimensions here on how big the cone can be to stop things getting too large, but even the restrictions in play were enough for teams to extend the diffuser edge up until now.

Stopping a crazy tech war

As part of correspondence that is understood to have been submitted to the FIA, Ferrari warned that if the Mercedes idea was given the all-clear then it could open the door for some more left-field solutions.

Sources have revealed one of these included having the serrated spiked areas at the very edges of the floor area, which could then put them in proximity of the wheels of other cars and that could risk punctures being caused by contact.

It was the possibility of designs getting out of control like this if action was not taken that is understood to have triggered the FIA's clarification in not allowing the floor stay/edge radius trick to be exploited for aerodynamic purposes.

Coming into force with immediate effect, the clarification from the FIA is understood to have prompted both Mercedes and Racing Bulls (above) to make some adjustments to their diffuser designs.

Haas is understood, however, not to have had to make any modifications as its design (pictured above compared to the Mercedes version, both from Barcelona) was not as extreme.