Apr.20 (GMM) After a low-key start to the 2013 season, Romain Grosjean is using a new Lotus chassis this weekend in Bahrain.

The Frenchman, although no longer derisively referred to as the 'first lap nutcase', has struggled for pace so far this year as teammate Kimi Raikkonen troubles the very top of the world championship.

Romain Grosjean, Lotus F1 E21
Romain Grosjean, Lotus F1 E21

Photo by: XPB Images

Grosjean, 27, has insisted he sensed a fundamental problem with his black and red E21, and so team boss Eric Boullier ordered a new one be built up for him for Bahrain and beyond.

Asked if the car or Grosjean's confidence is the real problem, Boullier said in Bahrain: "It's a whole package. We try to find out.

"He's not as his best, let's say, where we think he should be.

"There's nothing to blame, actually to finger-point anything, it's just the addition of different things."

Another theory is that Finn Raikkonen, the 2007 world champion who spent 2010 and 2011 away from Formula One in rallying and Nascar, has simply stepped up a notch into unprecedented form.

Asked to explain the difference between Raikkonen's 49 points versus Grosjean's 11 so far in 2013, Boullier told F1's official website: "Most of it comes from the fact that Kimi's speed has improved even further from last year.

"And Romain is struggling a bit with the 2013 tyres, to take the best out of them in one lap and on the long runs."

On Friday in Bahrain, even with Grosjean now in a new chassis, Raikkonen was consistently a few tenths faster in the practice sessions -- and indeed fastest of all.

Grosjean told France's RMC Sport: "We decided to change the chassis to remove all the doubts.

"But, really, we don't know what the problem is and why I can't use these tyres properly. The team has asked me to drive slower but I've already been driving like my grandmother.

"To be honest, the only thing that can explain what is happening is my driving style.

"For sure it's not easy on the mental side, but I still know what I'm capable of and that I'm not suddenly a second slower than Raikkonen."