Lewis Hamilton just gets better and better.
That's the view of Mercedes chief Toto Wolff, who has presided over Hamilton and his team's recent domination of Formula One.
Toto Wolff praises Lewis Hamilton's 'personal development' off the track
But Mercedes director has 'a lot of worries' ahead of new season
Wolff calls it 'healthy skepticism'
F1 season starts March 25 in Australia
The German manufacturer has won 62 of the last 79 races, completing a clean sweep of the Formula One drivers' and constructors' world titles since 2014, with Hamilton taking the championship on three occasions in that time.
"One of the things that impresses me the most with him is his personal growth," Wolff told CNN's The Circuit during testing in Barcelona.
"He gets better within the team every year. He has become an integral part. He's motivating the guys if they need to be motivated, rather than the other way around."
Hamilton's relationship with teammates in the past, particularly Nico Rosberg and Fernando Alonso, has sometimes been fractious.
"Don't expect an easy ride," Rosberg memorably said last year, when asked to offer his Finnish successor Valtteri Bottas advice on dealing with Hamilton at Mercedes.
Today, though, Wolff contends that you cannot underestimate the importance of the reigning world champion behind the scenes.
There is a "a superstar phenomenon" in sport where some athletes "are not really part of the team and with him it's the opposite," said Wolff, who is officially Mercedes' executive director. "For a year, he has been a very important pillar.
"It's like all of us -- if we are good in the head, everything is much easier. He is a high-performance person. He needs to be in the right spirit, energized and motivated. In the last few years, he has been there. And as far as I'm aware, he is in a good place."
Bottas 'stepping up'
For all of Hamilton's "personal growth," Wolff still believes Bottas can be a "strong challenger" this season, despite finishing the last championship 58 points behind in third place.
"We tend to underestimate that he was drafted in very late last year," says Wolff, having lured Bottas in January 2017. "Insofar as that, he has had a good season: Three race wins, three dominant race wins.
"He's become a solid part of the team and now it's about stepping up a little bit and seeing where he is."
Asked whether contract renewal would hinge upon a good start to the current campaign, Wolff wouldn't be drawn.
"I wouldn't want to think about the drivers' situation for next year because the moment you start to think about another pairing, you are not pushing enough anymore to give your drivers the best possible support," he said.
"We discuss it all the time, but with these guys, at Formula 1 level, you don't need to remind them. They know exactly."
'Keeping the diva'
For Wolff, "the moment you stop improving is when you should call it a day."
No wonder he is eager to hone the winning formula of the current car -- despite 15 pole positions and 12 wins last season.
"I've said she was a diva because she was very quick, but not behaving," smiles the Austrian. "I would like to keep the character traits of the diva, but make her behave a little bit more."
Wolff acknowledges the divisive "halo" cockpit safety system -- implemented this year to protect drivers from flying debris and other potential hazards -- "doesn't look very good" but he concedes you "can't compromise" when lives are at stake.
"It's a massive improvement for driver safety," Wolff says. "It has an effect on the car because it's pretty high up. The center of gravity has come up a little bit, which makes the setup of the car a little more tricky, but it's not a massive difference."
A team of '1,500 superstars'
Wolff demands high standards from himself as well as the car and drivers, looking into the mirror "every evening."
"Once you stop questioning and doubting yourself, you will not grow and you will not improve," he says. "You just have to find the right balance."
"I think I do it myself a lot, it's part of me, but I have a wife at home who will always push me back to the ground if needed."
The growth Mercedes subscribe to is holistic. It's important, he stresses, to remember the German marque is a team not of two superstars but of "1,500 superstars."
"Within the team we have a very open management culture," he explains. "We are able to spot and call the inefficiencies and deficits."
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Fans and rivals alike have condemned the dearth of close competition in the last four years, with F1 managing director Ross Brawn warning he foresees "a continuation of the steamroller."
Only Ferrari have achieved the double in five consecutive occasions, from 2000 to 2004 when Michael Schumacher was at the peak of his powers.
But while he claims there's "zero" chance of complacency from his team, Wolff says he still has "a lot of worries."
"We are always skeptical about whether we have done a good enough job with the car," says the 46-year-old. "Whether we have taken the right decision and not overseen any potential technological loopholes... it's that healthy skepticism where you constantly doubt yourself."
Wolff has been criticized for his part in overseeing this current period of hegemony, with the former F1 CEO Bernie Ecclestone saying: "I blame Mercedes and Toto for putting us in the s**t we are in terms of the competition."
The Austrian, though, just wants to keep on winning.
"You need to set targets, especially after having four years of success," Wolff says. "You need to set the right objectives in order to energize yourself and the company.
"And yes, we want to continue be at the very forefront, win races and eventually be in a position to fight for the championship."