Leading Formula 1 teams could be forced to revise their suspension systems on the eve of the 2017 season following a Ferrari query over technology pioneered by Mercedes.
The champion team is among those developing fully-legal hydraulic systems to improve chassis stability following the effective ban on FRIC (Front and Rear InterConnected) suspension in 2014.
Mercedes has placed a heave (or third suspension element) behind the rocker assembly to control vertical displacement of the suspension.
The benefits of the system were clear in 2016, but it is now under the microscope after Ferrari queried the use of such concepts in correspondence with the FIA before Christmas.
Red Bull could also be affected, having managed to exploit once again the radical rake angles integral to its aerodynamic concept.
Writing to the FIA to discuss whether new ideas on other cars are legal is common practice for F1 teams.
FERRARI'S QUERY TO FIA
In a letter to F1 race director Charlie Whiting, circulated to all teams, Ferrari's chief designer Simone Resta said his team was considering a system that could replicate FRIC without a physical connection between the front and the rear of the car.
The issue was whether these systems breached the catch-all article 3.15 of F1's technical regulations that effectively outlaws moveable aerodynamic devices, as they could help the car's aerodynamic characteristics.
"We are considering a family of suspension devices that we believe could offer a performance improvement through a response that is a more complex function of the load at the wheels than would be obtained through a simple combination of springs, dampers and inerters," wrote Resta.
"In all cases they would be installed between some combination of the sprung part of the car and the two suspension rockers on a single axle, and achieve an effect similar to that of a FRIC system without requiring any connection between the front and rear of the car.
"All suspension devices in question feature a moveable spring seat and they use energy recovered from wheel loads and displacements to alter the position of the heave spring.
"Their contribution to the primary purpose of the sprung suspension - the attachment of the wheels to the car in a manner which isolates the sprung part from road disturbances - is small, while their effect on ride height and hence aerodynamic performance is much larger, to the extent that we believe it could justify the additional weight and design complexity.
"We would therefore question the legality of these systems under Art. 3.15 and its interpretation in TD/002-11, discriminating between whether certain details are 'wholly incidental to the main purpose of the suspension system' or 'have been contrived to directly affect the aerodynamic performance of the car'."
Resta specified that Ferrari's concern was over components that exhibited either:
"1) displacement in a direction opposed to the applied load over some or all of its travel, regardless of the source of the stored energy used to achieve this.
"2) a means by which some of the energy recovered from the forces and displacements at the wheel can be stored for release at a later time to extend a spring seat or other parts of the suspension assembly whose movement is not defined by the principally vertical suspension travel of the two wheels."
WHITING: CONCEPTS 'CONTRAVENE' RULES
Whiting responded that any suspension system that acted in such a way was not in compliance with the regulations.
"In our view any suspension system which was capable of altering the response of a cars' suspension system in the way you describe in paragraphs 1) and 2) would be likely to contravene article 3.15 of the F1 technical regulations," he wrote.
Although Whiting's response would appear to outlaw the use of the trick suspension technology, it is understood teams affected have queried the situation.
As talks continue, any team running a device that could be interpreted as breaching the rules now faces a dilemma over whether to commit to it in its 2017 design but risk a final ruling outlawing the concept, or pursue an alternative system that may not be as competitive.
Additional reporting by Franco Nugnes