Mercedes' DAS: What is it, how does it work, and is it legal?

With pre-season testing comes intrigue. The two are inextricably linked as each Formula 1 team unleashes its new car for the first time under the media's gaze. Sure, the launch-spec cars offer visual differences over the old cars, and much of pre-season is an elaborate and expensive game of spot-the-difference - but that's before a wheel is turned.

Wheels were certainly turned at the start of testing this week at Barcelona - as were heads. As Lewis Hamilton barrelled down the Barcelona circuit's main straight on the second morning of 2020's round of testing, two unexpected things happened as the TV directors cycled through to his onboard camera.

Firstly, Hamilton seemed to pull his steering wheel towards him, despite it seemingly being locked in place by the quick-release mechanism. Secondly, the front wheels turned inwards automatically as the steering wheel edged closer to Hamilton's chest. Once Hamilton approached the corner, he pushed the steering wheel in once again - and, in response, the front wheels splayed out.

The mere push of the steering wheel and its desired effect immediately inspired numerous questions from within the F1 paddock: what does Mercedes' system do, how does it do it, and is it even legal? Let's expand on that.

Conveniently, a press conference featuring Hamilton and Mercedes tech chief James Allison had been pencilled in for the second day's lunch break. Unsurprisingly, those questions were fielded throughout. While Allison refused to be drawn on the specifics of the system, he did divulge the name - DAS, or dual-axis steering.

"It just introduces an extra dimension to the steering to the driver, that we hope will be useful during the year," explained Allison. "But precisely how we use it, why we use it, that's something we'll keep to ourselves."

The system should reduce drag and tyre scrub on the straights, while offering a healthy boost to driveability in the corners. One of the key mechanical changes that engineers can make to a car is the toe - the angle at which the front wheels naturally turn in or outward when looking at a plan view of the car. At its core, increasing the amount of toe-out (when the front of the wheel is further out than the rear) means that cornering should be a little easier as the wheel already leans into the corner.

Since the driver experiences a reduced slip angle (the difference between steering angle and the direction of travel) as a result, the steering inputs should be minimised. This arms the driver with improved grip and handling, and more confidence in the corners.

The 'how' is unclear at this stage. Whether the DAS ties in to the existing hydraulics or has its own mechanical device associated with it is not yet known

With a conventional suspension layout, there's always a compromise between toe angles and straightline speed. A driver needs to be able to deal with every kind of corner on the circuit, but without losing performance on the straights, so an adjustable system would prevent you being locked into a certain set-up.

The amount of toe change is also dependent on the Ackermann set-up for the steering. The Ackermann steering is the difference in turning rate of each wheel; pro-Ackermann is when the inside wheel turns more than the outside, while anti-Ackermann is reverse. The amount of toe a car can realistically run with also depends on that.

By pulling the steering wheel, that toe-out is reduced considerably, bringing the front wheels more parallel to lessen the amount of drag produced. With a lot of toe, the overall frontal area increases quite substantially, so the overall pocket of turbulence produced by their rotation also grows. In addition, because the wheels are running at a slight angle to the road, it increases the amount that they scrub along the ground, reducing overall tyre life as they're dragged along the straight. When the wheels are parallel, the frontal area drops.

The 'how' is unclear at this stage. On a conventional steering-rack system, operated by turning the steering wheel, the two steering arms are moved hydraulically and provide the lock required. With the DAS, the system must simultaneously draw both front wheels inward and outward as the steering wheel is pulled and pushed by the driver. Whether that ties in to the existing hydraulic system or has its own mechanical device associated with it is not yet known.

Part of the initial media room chatter when Mercedes' steering system became apparent concerned its legality. One particular technical regulation that did the rounds on social media was regarding suspension geometry, particularly Article 10.2.

Article 10.2.3 states that "no adjustment may be made to any suspension system while the car is in motion", which DAS would appear to contravene. But when it's considered as a steering system rather than a suspension system, the lines begin to blur.

Allison also explained that Mercedes had been in contact with the FIA about developing the system, and feels that F1's governing body will deem it legal.

"This isn't news to the FIA," Allison said, "and it's something that we've been talking to them about for some time. The rules are pretty clear about what's permitted on steering systems, and we're pretty confident that it matches all of the requirements."

Hamilton, after his first experience of the DAS system on Thursday morning, added: "I don't have a lot to really talk about with it. We're just trying to get on top of it and try and understand it.

If the DAS is cleared, rival teams have two options: one, to reproduce the system themselves; or two, protest it and hope the FIA opts to ban it

"The FIA are OK with the project. For me it's really encouraging to see that my team is continuing to innovate and stay ahead of the game. I think that's just down to the great minds that we have working in this team. Hopefully it will work."

While the FIA will monitor the system, especially as it presents safety concerns given the back-and-forth travel of the steering wheel, Hamilton explained that he had "no problems" when using it. The steering wheel could, conceivably, be pulled clean off the rack should the lock system fail, but Mercedes will make its case should anyone make a formal protest about the specifics of the DAS geometry.

One thing's for sure: the DAS has everyone's tongues wagging. In usual F1 procedure, the system will be queried by a team - or a collection of them - with the FIA to check its position on legality. If it's cleared, that team has two options: one, to reproduce the system itself for its own car; or two, protest it and hope the FIA opts to ban it.

But as Allison explained, the DAS is just one innovation aboard the Mercedes W11.

"I think one of the things that's not greatly appreciated is each of the new cars we bring to the track are just festooned with innovation, it's just they're not as obvious to you as a discrete standalone system like this where you can see it with your own eyes," he said.

"One of the things that gave me massive pride is to be part of a team that doesn't just turn the sausage handle each year, that is looking each year at how we can learn fast enough to bring all these innovations to the track and make them stick. This is fun, but it's only the tip of an iceberg of similar stuff that's across the car."

If the story of a famous cruise liner is anything to go by, icebergs can sink very big ships. Mercedes will be hoping that its own iceberg of developments will leave its closest challengers floundering in the depths.