Mercedes admits its initial optimism about the new underbody introduced in its W15 car at Spa may have been misguided due to the team’s disappointing performance at Zandvoort.

The Brackley-based team tested the new aero element in practice for the Belgian Grand Prix on Friday, but ultimately decided to revert to the previous specification of floor for the rest of the weekend.

However, the positive data collected in Spa encouraged Mercedes to use the updated component for the entire Dutch Grand Prix last weekend. However, the results were not optimal: George Russell and Lewis Hamilton finished their race on Sunday in a distant seventh and eighth place.

The disappointing performance inevitably raises new questions about whether the new floor design may be doing more harm than good, even despite the element generating more downforce.

Mercedes technical director James Allison has suggested that the underbody may be causing negative balance, which could ultimately lead to an overall loss of lap time.

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In the usual debriefing video from Mercedes on YouTubeAllison explained that the team is still working hard to understand exactly how the new floor will affect the car’s performance.

“The simple answer is we don’t know for sure,” Allison said. “You can do some simple measurements and say the downforce it was supposed to provide appears to have been there.”

“So, at first, you could assume that it worked as expected.”

Allison discussed the complexity of aerodynamics and vehicle balance that goes beyond simply generating downforce.

“The speed of the cars this year depends mainly on their handling.

“So the question is not just does your aerodynamic package give you downforce, but does it give you the balanced car you need in the corners. Does it give you the balanced car you need from high to low speed?”

The balance problems became apparent at the Dutch Grand Prix, where both Russell and Hamilton struggled in qualifying due to poor car balance, which led to tyre overheating.

Allison highlighted the impact this instability had on her performance.

“We definitely know that our car was not well balanced this weekend,” he added.

“That’s where most of our speed was lost. Whether it was the new floor, the new aero package or not, we need to keep an open mind and look at it again at future races.

“At the moment we know it measured downforce, but we are not sure if it delivers a good balance. We will have to look at that more closely over the course of the year.”

The problems were particularly pronounced in qualifying, with Allison describing how the car’s erratic handling affected her ability to extract maximum performance from her tires.

“For some reason we managed to build a car that was too vulnerable,” commented the British engineer.

“The rear was leaning too much towards breaking away, so when the drivers tried to accelerate it, the rear lost grip and contact with the road. And in qualifying they have to lean on the car and we could do a really good lap if they could just somehow keep this very sharp car on the rails.

“Just a tiny slip of the rear wheel caused by a gust or whatever and the rear tires will burn. The temperature of the rubber surface increases dramatically with a tiny slip.

“Once the surface temperature is high, it doesn’t recover for several corners. At Zandvoort, the corners come at you thick and fast and there are no really long straights for them to cool down on. And so a lap is over with a crack.”

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