Ammon News - Angst in Austin is an unfamiliar emotion for Lewis Hamilton but the Mercedes team principal, Toto Wolff, is worried that engine problems could thwart the British driver’s title hopes.

This is usually a productive circuit for Hamilton, who has won five of the eight contests held here and often cites it as one of his favourite races. Yet Mercedes’ reliability worries cast a shadow over the buildup to Sunday’s US Grand Prix on an unusually tetchy practice day.

The rivalry between Hamilton and Max Verstappen threatened to boil over when the two went wheel-to-wheel in the second practice session on Friday, prompting Verstappen to give Hamilton the middle finger and exclaim over the radio: “Stupid idiot!”

It was a sign of the tension between them after the world champion was overtaken at the top of the standings by Verstappen in Turkey two weeks ago. Hamilton’s Mercedes dropped 10 places on the grid as the punishment for a fourth engine change of the season and he while Verstappen was second. That outcome means the Red Bull driver holds a six-point lead over Hamilton with six races remaining.

Mercedes dominated the first practice session in Texas, with Valtteri Bottas quickest and Hamilton next, while Verstappen was almost a second slower. But Wolff’s delight at his drivers’ superior straight-line speed was tempered by anxiety over technical issues. Bottas – third in the standings and the victor in Turkey – was handed a five-place grid handicap on Friday for using a sixth internal combustion engine this year – three more than the regulations permit. It is the Finn’s third penalty in four races.

“I think you see that we are suffering on the reliability this year,” Wolff said. “This year it has really hit us hard.” He declined to go into detail about the specific problem. Two other drivers with Mercedes engines – George Russell of Williams and Aston Martin’s Sebastian Vettel – are also being penalised this weekend for using replacement parts. Verstappen started the Russian Grand Prix last month from the back of the grid after exceeding his season’s allocation of several parts, including a Honda engine.

“We are trying to get on top of the problems, and we haven’t understood fully,” Wolff said. “We are trying to push the performance every year and this year we’ve come to a point where it has cost us points, but over the last 10 or eight years that mindset has won us races and championships.”

The technical issues present a dilemma for Mercedes with the title race so finely poised. Replace Hamilton’s engine once more and they risk a repeat of Istanbul, with a fresh penalty likely to deny him a podium finish and give Verstappen the opportunity to extend his lead.

But in the worst-case scenario of a fault forcing Hamilton to retire while Verstappen wins and records the fastest lap, the resulting 26-point boost for the Dutchman would be potentially disastrous for Hamilton’s prospects of a fifth successive world title. “Obviously the risk is still there. What’s difficult about it is, do you want to pre-empt the situation and take another penalty, take the hit, or do you want to run it and then possibly risk a DNF? That is a discussion that is happening,” Wolff said.

The Circuit of the Americas provides ample overtaking opportunities allowing for progression from the back of the grid, but the subsequent race, Mexico City on 7 November, is at high altitude, which places additional strain on engines. Verstappen has won there twice.

The early years of his Formula One career were stained by frequent collisions and accusations of an over-aggressive attitude. Verstappen’s former Red Bull teammate Daniel Ricciardo believes the 24-year-old has matured, even if clashes with Hamilton this year at Silverstone and Monza – the latter viewed as Verstappen’s fault – reignited talk of a belligerent style that his behaviour on Friday seemed to exemplify. “There was that stage in, I’d say, Max’s young career, when he had the speed but there was still a few – call it mistakes, or a bit of over-anxiousness or eagerness,” said Ricciardo, who now drives for McLaren. “2018 was really that year where he kind of learned from that and then the second half of his season was really strong. You could see that click in maturity on track. And the last few seasons for him have been pretty immense.”

*theguardian