Ferrari said the 2007 champion, whose last win was at the Circuit de Catalunya a year ago, would get a lighter chassis than Brazilian team mate Felipe Massa [ Images ] for the start of the European season.
"The reason only Raikkonen will use it is that...his natural physique and height means he weighs more than Felipe Massa and therefore it is more of a challenge to accommodate the additional weight of the KERS system on his car," the team said on their website (www.ferrari.com).
Ferrari, who have endured their worst start to a season with no points until Raikkonen finished sixth in the fourth race in Bahrain, said safety had not been compromised and the new chassis had passed a mandatory crash test.
The new KERS system, which offers drivers a short boost of power at the push of a button, weighs between 25 and 30kg and has been used by only a handful of teams so far, including Ferrari.
Cars must weigh no less than 605kg at all times during a race and drivers use ballast, which can be moved around for ideal weight distribution and balance, to bring them up to the legal minimum.
The lighter the car and driver, the more flexibility there is in setting up the car to suit the track and driver's style. Ferrari expect KERS to be an advantage in Barcelona [ Images ].
The team said they would also have a new aerodynamic package with a rear diffuser similar to the controversial one used by leaders Brawn GP and that several teams, including the champions, tried to ban earlier in the year.
"It is only a first attempt at designing a part that was not part of the initial design, but is now a required element following the new clarification of the rules," said the team.
Ferrari, who tried out the new diffuser for the first time at Vairano in Italy [ Images ] on Saturday as part of a permitted straight-line test, said initial results indicated the car would be quicker.
However, fitting the new diffuser had been far from straightforward.
"The engineers have had to redesign much of the electronics and hydraulics systems at the rear end of the car, in order to relocate components to make way for the new diffuser," the team said.
"This redesign has been a more complicated procedure than designing, producing and fitting the diffuser itself."