Mercedes director James Allison has explained that the team is trying hard to understand the impact of the new underbody on the W15 F1 car. At the Dutch GP in Zandvoort, the underbody is said to have disrupted the “balance” of the car and thus significantly reduced the lap time.

It is the same surface that was introduced for the Belgian Grand Prix before the summer break, but Mercedes decided not to use it for the race that saw Lewis Hamilton take the win after the surface produced mixed results in free practice.

Mercedes designed the new underbody to increase the car’s downforce. Realising the effectiveness of this underbody, they reintroduced the key aerodynamic component for the Dutch GP. However, the additional downforce had unintended side effects and the team ended up in the midfield. George Russell finished seventh and Hamilton eighth.

In a Mercedes debriefing video, Allison explained that the team is studying the underbody more closely to better understand it for the upcoming races. When asked how the underbody was behaving, he told Motorsport.com:

“The simple answer is, we don’t know exactly.

“You can do some simple measurements and say that the downforce it was supposed to deliver was apparently there. So on one level you could assume it was working as expected.

“But the speed of the cars this year is largely down to how well they handle. So it’s not just about whether your aerodynamic package gives you downforce, but whether it gives you the balanced car you need in the corners. Does it give you the balanced car you need from high to low speed?

“We definitely know that we didn’t have a well-balanced car this weekend. That’s why we lost most of our speed. Whether that was due to the new floor, the new aero package or not, we have to keep an open mind and that’s something we’ll have to revisit in 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.”

One particular problem the team observed with the W15 was the extremely heat-sensitive rear tyres, which get hot even with the slightest slip. He added:

“For some reason, we managed to produce a car that was too fragile.

“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 the slightest slip of the rear wheel caused by a gust of wind or whatever, and the rear tires will burn. The temperature of the rubber surface increases dramatically with even the tiniest 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.”