Marcus Ericsson has revealed he is losing half a second per lap to team-mate Kamui Kobayashi in weight alone.

Driver weights have been the focus of much attention this season as the new regulations have led to much heavier cars and teams struggling to get down to the minimum weight of 691kg. Speaking about his relationship with team-mate Kamui Kobayashi at the end of testing in Bahrain, Ericsson confirmed to Crash.net that he was struggling to match Kobayashi's pace because of his weight.

"The problem is that he's 10kg lighter than me, so for me to be able to match his times is so difficult because I have half a second every lap which I'm losing just because of the weight," Ericsson said.

"So it makes life difficult. We're working all the time to try and make the car lighter as well so it's a constant work for us, but it's for sure a bit frustrating that you're not only a rookie but you have 10kg too much over a lap."

Asked if the car was running over the weight limit, Ericsson confirmed that was one area Caterham has to make progress.

"I don't know how much exactly but I know both cars are over the limit, and obviously he's 10kg lighter than me so my car will be quite a lot over the limit. It's losing us a lot of lap time, which is a shame."