AUSTIN -- Ferrari has denied accusations it was forced to adapt the way it runs its engine this weekend as a result of a technical clarification by F1's governing body, the FIA.
Ferrari has had a clear straight-line speed advantage all season, which is believed to be related to the Italian team's superior engine performance. At some circuits it has been valued at as much as 0.8s in lap time, but in Austin the advantage was considerably smaller.
Following six consecutive pole positions at recent races, Ferrari qualified second and fourth for the U.S. Grand Prix and struggled in the race, with Charles Leclerc finishing 52 seconds off race winner Valtteri Bottas while Sebastian Vettel retired.
The poor performance in Austin coincided with a recent clarification from the FIA over what is and isn't allowed regarding the fuel-flow meter -- the standard FIA device that monitors the rate at which fuel is consumed by the engine. The clarification was issued in the form of a technical directive after Red Bull raised questions over a way of potentially increasing the fuel flow to the engine beyond the 100kg per hour limit outlined in the regulations.
After Sunday's race, Red Bull driver Max Verstappen said he was "not surprised at all" by Ferrari's dip in competitiveness and went as far as alleging Ferrari had been cheating prior to the technical directive being issued.
"That's what happens when you stop cheating, of course," he told Dutch TV. "But yeah, they had a good look at it. So now we have to keep a close eye on it."
Reacting to Verstappen's comments later on Sunday evening, Ferrari team principal Mattia Binotto said: "I read and I heard a lot of comments this weekend about a technical directive and the impact on our cars. I heard comments at the end of the race which I feel very disappointed by.
"These type of comments I feel are completely wrong. It's not good for the sport and I think everybody should be a bit more cautious. Thanks."
Asked specifically if anything had changed on the power unit or the way it is operated as a result of the technical directive, Binotto added: "Nothing at all."
Ferrari driver Charles Leclerc, who was sat next to Binotto in the same press conference, hit out at Verstappen's comments.
"I think it's a joke to be completely honest," Leclerc said. "He has no clue. He's not in the team. So we know exactly what we are doing and I don't know why he's speaking, he doesn't know anything about us."
Binotto said there was nothing unusual about the technical directive and said his team had not even looked into the details of it ahead of this weekend's race.
"Honestly, we will look through the technical directive -- we have not done it this weekend in detail, we've seen I think it's number 35 of the season. It's a process where teams may ask clarification to the FIA and the FIA is replying. Will it have more of an impact in the race or quali, I don't know. I am not able to answer you."
If Ferrari's rivals had been convinced the Italian team was cheating as Verstappen suggested, they could have launched a protest rather than seek clarification from the FIA. But speaking on Sunday night, Mercedes team boss Toto Wolff admitted his team could only base assumptions on speed traces as it was impossible to know exactly what is going on under the engine cover of the Ferrari.
"We just had a discussion about the data from the race and the speed trace [of the Ferrari] looks totally different to the last few races," he said. "But whether it's down to the technical directive or down to another issue, I honestly don't know as we can't look into what Ferrari has done."
Red Bull boss Christian Horner added: "The power unit is an incredibly complex piece of machinery -- both from a hardware and software perspective. The clarification we requested was standard stuff that goes backwards and forwards continually between the teams and the FIA.
"It's always good to get clarity before wasting effort [developing a solution].
"I think the technical directive was very clear. That's not to say anybody was doing anything, but if they were it would obviously be illegal."
Binotto said he did "not yet" have a full explanation for Ferrari's lack of pace in Austin, but admitted the team may have got its trade-off between downforce and drag wrong.
Drag is another major factor influencing the straight-line speed of an F1 car and the Ferrari has less drag than its rivals, making it quicker on the straights. But the trade-off for that extra straight-line speed is that it is often outgunned by Mercedes and Red Bull in terms of overall downforce, and in trying to find the right balance this weekend, Binotto said Ferrari may have made an error.
"It's true that we were not gaining on the straight as much as in the past races, but true as well that I think we matched our competitors in cornering -- at least in qualifying," he said. "The trade-off between grip-limited and power-limited has been moved this weekend as a test on our side. "We were competitive in qualifying and now there is something in the race we need to understand and then see what's best for the next races in terms of the trade-off."