BARCELONA (AFP) - Lewis Hamilton has admitted that he is punching below his weight as he struggles to understand how his Mercedes car reacts to this year's tyres.

The world championship leader and defending four-time champion told reporters on Thursday that he has not given any thought to his position after his lucky win at last month's Azerbaijan Grand Prix.

"That is the last thing on my mind right now because I am more concerned that we can get on top of all the issues," he said.

"I have zero comfort and, since the last race, I have not thought for one second that I am leading the world championship.

"It's not in my mind. It's not that it is not important to me. It is just empty at the moment.

"There is a long, long way to go. Imagine if I got excited now, knowing that we still have all the problems, it doesn't mean anything. What is important is where you are in the end of the year.

"If this weekend, we happen to have got on top of the issues we have with the car and we start to be more consistent, then I can be a lot happier because I know then I can punch either at my weight or a little bit above my weight.

"At the moment I am punching below my weight and that is not sufficient enough to win a world championship.

"We have been capitalising on circumstances like the outcome of the last race so I will take it for now, but in the long term the team cannot continue to rely on that."

He said his difficulties in finding a competitive and consistent set-up with his Mercedes W09 car were proving to be elusive to solve.

"I can't really expand too much on it because if we knew it all, we could fix it. We are constantly working on a solution. It is interesting, but the underlying factor is down to how we use the tyres."

Hamilton dominated the season-opening Australian Grand Prix, but a computer software glitch cost him victory and he has struggled since.

He was gifted victory in Baku thanks to his rivals' misfortunes Hamilton leads his main rival Sebastian Vettel of Ferrari, a fellow four-time champion, by four points after four rounds in this year's title race.