Red Bull team principal Christian Horner believes the "high-speed" corners of the United States Grand Prix will 'limit' Mercedes ability to utilise its trick suspension.
Despite Sergio Perez topping second practice on Friday, it was Valtteri Bottas' FP1 benchmark that remained the fastest time of the day.
In the first session, Mercedes were utterly dominant, with Max Verstappen the best of the rest but still almost a second off the pace before FP2 suggested the playing field had been levelled.
After FP1, considerable focus was placed on Mercedes' rear suspension which lowers the rear wing and diffuser assembly, eliminating the rake and drastically reducing drag.
“It’s not quite as extreme as what we saw in Istanbul [the Turkish GP] but you can certainly see that it's something they are still using," Horner told Sky Sports F1.
"The high-speed nature of some of the corners here limit its use to some extent. But they’re obviously making good use of it.”
Red Bull time "90 per cent" lost on the straights
In a fierce battle for the drivers' and constructors' world titles, Red Bull and Mercedes have both raised questions over the design of their rival's cars.
On this occasion, Horner is satisfied it adheres to the regulations, stating: “It doesn’t appear to [contravene the rules], so we don’t have an issue with it.
"There were obviously some straight-line speeds at the last race that were quite eyewatering and I think with further analysis we were able to understand how they were achieving that at that type of circuit.”
Although Red Bull believe it understands how Mercedes is generating such speed, this has not enabled the team to find an answer in the two weeks since Turkey.
"It's significant, 90 per cent of it is down the straight," said Horner. "Are they just running a higher engine mode or is it the system that they're activating now?"
A saving grace for Red Bull and Horner appears to the fragility of Mercedes' power units, with Valtteri Bottas taking a five-place penalty for the fitting of a sixth internal combustion engine this season.
"It's not usual for them to run their engines as hard as they have," assessed Horner.
"They're running them harder, there's a significant difference in straight-line speed.
"It's not just down to the engine, they've dropped their rear height in Turkey. We've just got to make sure we get the best out of our car and I think there's more performance to come."
What do you think?
Short spice & the Helmut out thought by Mercedes, clever engineers earning their dosh.
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