F1 analysis: What we’ve learned about DAS from RBR protest

Late on Friday evening the FIA Formula 1 stewards rejected Red Bull Racing’s protest of the Mercedes DAS system. We take a look at what that decision tells us about that innovation.

The stewards ruled that 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 focussed essentially on whether DAS is considered as a steering system, or part of the 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.

Before looking into the FIA document, it’s also worth recalling what Allison said in answer to a question from a fan in a Mercedes video Q&A last month. He 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: “We have a very inventive chief designer, John Owen, and he took one look at that challenge. John reckoned he could do it, put it out to our very talented group of mechanical designers, and between them they cooked up two or three ways in which it might be done.

“We picked the most likely of those three, and about a year after that out popped the DAS system that you saw at the beginning of this season…”

Mercedes AMG F1 W11 DAS steering

Photo by: Giorgio Piola

The Red Bull theory

In making its protest Red Bull was obliged to state its case, in other words explain how the team believes the system works, and why it believes it to be illegal. This was the first time that a rival team had formally outlined its theory, so it’s worth repeating here:

“DAS appears to work by changing the toe angle of the front wheels. This is separate in effect to the traditional steering system as it does not involve movement of the steering rack pinion gear.

“A conventional steering system can navigate a lap of any circuit […] In isolation DAS is incapable of lap navigation and is therefore dependent upon the conventional steering system – i.e. DAS, in changing the toe angle of the wheels, is a separate and redundant system.

“Alteration of the static toe angle on the front axle will also change the aerodynamic characteristics of an F1 car, 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: “By observation of the video footage from FP2, use of DAS was not every lap and isolated to in/out or re-charge laps thus it was not a system necessary for use in timed laps, rendering the primary purpose to be something other than steering.

“The Technical Regulations do allow multiple steering systems. Red Bull 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.”

Finally Red Bull went to the core of the matter, and what DAS achieves: “A key discussion point must be why have Mercedes added the DAS system? As mentioned above, judging by practice today, it appears to be used on out and slow laps as a means of adjusting tyre temperature, ie its primary purpose is not as a steering system but rather a tyre temperature management system.

“In conclusion, 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

Mercedes was in a tricky position. The team must have been fairly confident that DAS would be passed legal – after all as Allison explained, the idea of moving the steering wheel back and forth actually came from the FIA…

Since that initial discussion there would have been endless 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 short and technical Mercedes 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 tackled the question of suspension thus:

“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 went on to show that DAS is indeed a steering system with the following arguments:

“1. Actuating conventional steering moves the wheels in the same direction.

“2. Actuating DAS moves the wheels in the opposite direction – it is like changing the static toe angle of the steering system

“3. Conventional steering often also changes the toe – but it does so as a function of steering angle.

“4. Changing the toe angle of the wheels changes the forces on the front tyres.

“5. 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.

“6. 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.

“7. 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.”

Most of that was a simple description of the system, but nevertheless it was useful to have it in the words of the team, and the reference to toe in cornering was interesting.

The stewards’ conclusion

Much of the stewards’ conclusion was devoted to explaining the significance of the difference between a steering and suspension system, 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.”

While Red Bull – like most observers – assumes that the primary purpose of DAS relates to control of tyre temperature, Mercedes has avoided making any reference to that 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 Red Bull 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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