Late on Friday evening the FIA Formula 1 stewards issued their decision regarding Red Bull Racing's protest of the DAS system used by Mercedes during free practice.
The punchline was that the protest has been rejected, and thus Mercedes - and any other team that is developing it - can run a DAS system until end of this season, before it becomes illegal for 2021.
How the stewards reached that decision was explained in a lengthy document that outlines a philosophical argument between the two teams that focused essentially on whether DAS is considered as a steering system, or suspension.
It's fascinating to see how two brilliant technical directors, Adrian Newey and James Allison, could take such different views.
While the legal arguments are intriguing, what was more useful about the document was what Mercedes was obliged to reveal about its system - and what Red Bull told us about how Newey and his Milton Keynes colleagues believe that it works.
Allison, in response to a question from a fan in a Mercedes video Q&A last month, revealed that the concept of moving the steering wheel back and forth to alter the toe actually originated with the FIA.
"In fact we first wanted to introduce this in 2019," he said. "We took our ideas to the FIA, showed them, explained why we thought it was legal. And they begrudgingly agreed that dual-axis steering was actually legal.
"But they didn't much like the way we'd done it, because the second axis we were getting from a lever on the wheel, rather than that whole wheel movement.
"And so they said, 'No, you're going to have to move the whole wheel in and out.' And I think when they said that they were hoping that would be too difficult, and we would go away and cause them no more problems."
Mercedes was not so easily discouraged, and Allison credited chief designer John Owen for coming up with a solution that the FIA then declared legal during pre-season testing.
The Red Bull theory
In making its protest Red Bull was obliged to explain how the team believes the system works, and why the team believes it to be illegal.
As soon as DAS was first spotted in Barcelona testing, media and fans indulged in heavy speculation about the system's workings, but this was the first time that a rival team had formally outlined its theories.
Red Bull theorised that DAS was a dynamic toe-change device, separate to the normal steering system which uses the rack and pinion to shift the steering arm from one side to the other. Furthermore, it suggested that the DAS system would not count as a steering system as it could not, on its own, navigate a lap of the track.
"Alteration of the static toe angle on the front axle will also change the aerodynamic characteristics of an F1 car," Red Bull continued, "typically performed in set‐up and prohibited in Parc Ferme.
"DAS operation, which is a front axle toe angle modifier, will have a measurable aerodynamic effect on the car, whether changing the trajectory or not.
"A steering system should alter a car's trajectory when used. Observation of DAS usage in FP2 indicated deployment in a straight line with no change of trajectory, thus rendering DAS not a steering system."
A conclusion from Red Bull, and one that has been reached by others, was that DAS is not used all the time, "rendering the primary purpose to be something other than steering".
"The Technical Regulations do allow multiple steering systems. RBR contend a steering system should have the primary purpose of being able to steer the car. A secondary system that is, on its own, incapable of steering the car is an unnecessary system."
Ultimately, Red Bull's assertion was that DAS is not a steering system, but is used to control tyre temperature - and therefore constitutes as a tyre temperature management system.
"In conclusion," the team wrote, "DAS is an unnecessary, separate system requiring a separate driver input and using components which are separate in their effect to the main steering system."
The Mercedes defence
Since Mercedes' initial discussion with the FIA, there had been further correspondence with FIA technical boss Nikolas Tombazis, who was fully up to speed with the system and obviously believed it to be legal.
However, Allison and his colleagues could not take anything for granted and anticipating a protest had prepared a strong case for the stewards, who have the power to overrule Tombazis.
The problem in such cases is that in proving something is legal you have to go public with information that you would rather keep to yourself - so then it becomes a question of how much you reveal.
The Mercedes defence was short and very technical, and basically tackled the grounds for protest cited by Red Bull by first demonstrating that DAS is not a suspension system, and then proving that it is a steering system.
Mercedes' defence hinged on the following points:
"1. It is mounted on the fully sprung side of the car and plays no role in suspending the car, or insulating the car from the undulations on the road surface
"2. It is mounted fully on the power assisted steering rack.
"3. All it is capable of doing - just like a traditional steering system - is to alter the alignment of the front wheels about the kingpin axis by changing the position of the outboard ends of the steering rack.
"4. It cannot change the length of any of the suspension members."
Mercedes then explained that "actuating conventional steering moves the wheels in the same direction, [while] actuating DAS moves the wheels in the opposite direction - it is like changing the static toe angle of the steering system.
"Conventional steering often also changes the toe - but it does so as a function of steering angle. Changing the toe angle of the wheels changes the forces on the front tyres.
"Any driver knows that changing the toe makes the car change its steer response (from lazy to nervous) - changing this value while the car is manoeuvring (in corners or on the straights) will cause the car to steer.
"This is because under all track conditions (except the purely hypothetical situation of zero wind and geometrically perfect track), the difference in load on the tyres from left to right will cause the car to steer when the toe angle is changed.
"DAS is a steering system that allows the driver to optimise the toe, and therefore the steer response of the car during a run instead of being confined to changing only from run to run."
The stewards' conclusion
Much of the stewards conclusion was devoted to explaining the significance of the difference between a steering and suspension system, and how and why certain rules would be breached if the FIA declared DAS to be part of the suspension.
Contained within that was a little more description of how it works: "The DAS is hydraulically-assisted like any conventional F1 steering system, but remains under the full control of the driver at all times. Physically, the DAS is integrated with the conventional steering system of the car.
"Mechanically, the DAS re-aligns the two front wheels via the same central mechanism that conventional steering does. The fact it acts on the track rod is, we believe, entirely equivalent to the conventional steering.
"A hydraulically-powered DAS which remains under the full control of the driver is also entirely consistent with the hydraulically-powered conventional steering system."
The stewards added: "Changes in toe affect the direction of the car in two ways: A. If toe changes in a corner, the effect will be asymmetric and hence the trajectory of the car will change. B. If the driver applies a steering wheel (rotational) input, the response of the car will depend on the toe angle of the wheels, hence the fore‐aft position of the DAS will have a direct steering effect."
The protest has had the side-effect of explaining more into the workings of DAS, despite Red Bull's assertion - like most observers - that its primary purpose relates to control of tyre temperature. It's worth noting that Mercedes has avoided making any reference to that, at least in the argument reported by the stewards.
The question now is which other teams have DAS systems in development, and indeed which teams can fit one within the existing architecture of their cars? And can it be done in the context of the freeze of mechanical components that is about to kick in?
Christian Horner implied that Red Bull has a DAS programme underway. Indeed one could argue that his team had a pretty good idea that its protest would be rejected, and that and it was a "fishing exercise" to get as much information out of Mercedes as possible.
In truth RBR has probably learned little from the document that we've seen - what we don't know is if anything else came up in the discussion with the stewards that proved useful to Newey and his colleagues.
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