Ferrari have made improvements in all areas and their new Formula One car is a "completely different story" to the one that drew a dismal blank on the track last year, Kimi Raikkonen said on Tuesday.

"The whole package is quite a bit better from where we finished last year. We've improved in all the areas," said the 2007 world champion after his first day of testing at the Jerez circuit in southern Spain.

"We have a lot of things to do and things to improve, but it's definitely a positive start and we have something to work with."

Ferrari failed to win a grand prix last year for the first time since 1993 and Raikkonen endured his worst season in the sport, finishing 12th overall and without a single podium appearance.

The team had three team principals last season in a major shake-up, with the most recent Maurizio Arrivabene arriving in November.He has set a minimum target of two wins in 2015.

Germany's four times world champion Sebastian Vettel has arrived to replace Spaniard Fernando Alonso and lapped fastest in the first two days of testing, although times are less important at this stage than mileage covered.

Raikkonen, who did 92 laps equal to 407 km on Tuesday, ended the day second fastest behind Brazilian rookie Felipe Nasr in the Ferrari-powered Sauber.

"You usually know if a car is good or not, and this year is a completely different story than last year as I had a good feeling straight away when I went out," said Raikkonen.

While Mercedes again completed the most laps, with Nico Rosberg doing 151 at the wheel on Tuesday, Ferrari's improved performance has been noted by their rivals.

"We are keeping an eye on the opposition, especially Ferrari has been an eye-opener in the last couple of days," said the German.

Meanwhile, Force India have admitted their new VJM08 car may not be ready in time for the second set of pre-season testing in Barcelona later this month.

The Silverstone-based team were the only absentees for the first four days of testing in Jerez this week, claiming that "learning opportunities" would have been limited. However, it now appears that they will run their 2014 car for the first four days of testing in Barcelona from February 19-22 with the hope of unveiling their new model for the final set of testing, also in the Catalan capital between February 26 and March 1.