Lewis Hamilton: Mercedes will face harder fight to retain title in 2015

Mercedes driver Lewis Hamilton is certain that the 2014 F1 world champions will face a tougher fight from their rivals this season.

The Brackley based team cruised to the title last season, with very little resistance from fellow competitors. The Mercedes team won 16 out of the 19 races in the season and took home the constructors' title a few races ahead of the finale.

Hamilton, who won the Drivers' championship ahead of teammate Nico Rosberg in the final race last season, is certain that they will face more competition this year. When asked about which team dominated the seven days of testing with the 2015 cars, he admitted that it is impossible to point to a particular team as the strongest.

However, the British driver did mention Ferrari and Red Bull were the most likely teams that will pose a threat to their title defence.

"Zero. I've not been looking at the others. [Pastor] Maldonado was quick today but everyone was on different tyres, different fuel loads," Hamilton said, as quoted by ESPNf1.

"Ferrari looks quite strong, similar to Red Bull, but I don't know where we are amongst those," the two-time world champion added.

The 30-year-old believes that the pecking order will be more clear during the final pre-season test, which begins in Barcelona on 26 February, ahead of the season opening race in Melbourne on March 15.

"Every time you come to test in winter the same question is asked and its really difficult to know because they put you out on high fuel, and then you have fuel taken out, so you don't have time to real dial the car in the way you really want to the way you do in a race weekend,"

"I think everyone will have a better idea next week when everyone brings their upgrade for the first race. Then when you get to the first race it's all different because the tyres start handling different. It's like juggling blind. That's what I love about this sport - I don't really know what's to come. I anticipate a harder fight this year, that's what I'm anticipating," the former McLaren driver concluded.