Driver: Pastor Maldonado / Valtteri Bottas
Chassis / engine: FW35-01 / RS27-5409/3
Location: Circuit de Catalunya, Barcelona 4.655km
Objectives: Aero evaluations and set-up work
Weather: Dry and sunny
Air & track temps: 2-17ºC / 3-28ºC

Day four of the Williams F1 team Barcelona test would again see both Pastor Maldonado and Valtteri Bottas sharing the driving and it would be Pastor who would run in the morning session. The morning session would see the team continue assessing various aero upgrades in his first run. Out on hard tyres Pastor would set a 1m:24.489 prior to pitting for more setup changes. His next run would see him improve with a 1m:23.986 while quickest was Rosberg with a 1m:21.277 followed by Alonso and Vettel both on soft tyres. Alonso would go fastest with a 1m:21.024 while Pastor running on mediums would improve with a 1m:23.817. Rosberg would respond to Alonso with a 1m:20.732 to again be fastest.

Pastor would try the super soft tyres of one of his runs but did not improve on an earlier time set of the soft tyre, 1m:22.415. Rosberg had also found time with a 1m:20.130 to remain fastest with Alonso second followed by Hulkenberg. Pastor's next run prior to lunch would be on the medium tyre as the team again tried each of the various dry compounds. The morning session would come to an end with Pastor completing his testing prior to the opening race in Australia.

Pastor has said that the new aerodynamic package added to the FW35 has improved the car. Among the new parts added to the FW35 was a Red Bull-style ramped exhaust.

Pastor said: “It’s even more easy this car. We have more downforce.”

Pastor added: “The car feels a bit different, the new aero package is quite big so for sure you feel the difference. It’s working quite good.”

Maldonado spoke of the increased downforce from the upgrade and how it could be felt on all types of corners. “I think we improve some particulars from the aero point of view I think it’s clear there is some gains on it."

The afternoon session with Valtteri out on the track and his first run would set a time of 1m:24.882 and he would pit. Upon his return he would set his quickest lap time to this point a 1m:23.605. He would pit again and would come back out for a run of the soft tyre. He would set a 1m:22.524 on this run to be just behind Pastor's morning time. There was an hour remaining in the session to complete the teams pre-season testing.

Mike Coughlan, Technical Director: We’ve concluded a very successful couple of tests with the FW35, without any major problems to stop us running. We completed the tests with one set of car parts, including using the same gearbox, so we have a good reliability record. We brought an upgrade package here and in race trim the car looks competitive. We’ll now analyse all the data we have and then will go to Melbourne with the best package for the elevated temperatures we expect to find.

Pastor Maldonado: Winter testing has been good for us. The FW35 has been very reliable but we are still learning how the car behaves. The FW35 is completely different to drive compared to the FW34, mainly because of the new Coanda exhaust. It has given us greater overall downforce but we still have a way to go to make sure we get the maximum benefit. We have a good base to work from though so now we just need to unlock the full potential of the car. We have some great data to compare from this year and last, so it’s all to do back at the factory now.

Valtteri Bottas: We were focussing on shorter runs today and I now feel ready for a qualifying session. We did a high fuel run at the end of the day but we are still working hard to get the most out of the package we have. Overall, it has been a productive winter test and I’ve achieved what I wanted to from it. The car has been really reliable and now I feel fully prepared for the start of the season.