LONDON • Mercedes are to investigate why Lewis Hamilton, the fastest Formula One driver of the modern era, is now not even the quickest man in their team.
He won his third world title with three races to spare. He took 11 of the first 12 poles and 10 of the opening 16 races but his team-mate Nico Rosberg finished much stronger.
The latter had three straight wins and pole position in the last six grands prix.
Rosberg's victory in Sunday's Abu Dhabi Grand Prix, when he finished 8.2sec ahead of Hamilton, was the most convincing of his six wins this season.
Mercedes motorsport director Toto Wolff said: "There has been so much discussion about whether Nico has stepped up his game, has the car come towards him or whether Lewis has taken it more easy.
"I think we have to do an intelligent list over the next couple of weeks to analyse why."
It could be a number of factors.
Rosberg has appeared even more single-minded since being beaten to the championship in Austin in October, when he was furious with Hamilton for being "extremely aggressive" on the opening corner of the US Grand Prix.
Hamilton, who has also admitted enjoying a great deal of partying in recent weeks, could have subconsciously eased off. But he is also unhappy with the way the car has developed since the Singapore Grand Prix in September.
After again losing out to Rosberg in qualifying in Abu Dhabi on Saturday, he said: "I have got this great graph which shows you all the races and all 12 of the opening races, the car was great.
"Since then, it has been terrible.
"I said to my race engineer, we need to sit down to figure out how we are going to rectify this."
Hamilton will still feel confident he can rediscover his old ascendancy for the start of the 2016 season. But he will feel better if he can work out why his form has faltered.
Wolff said: "After Singapore, we developed in a different direction and whether the car has come more towards Nico and gone away from Lewis, I don't know. It could be a factor but it could also be many possible factors."