Nico Rosberg of Mercedes posted the fastest time on Friday in the early stages of the final day of Formula One testing at Jerez in Spain.
Rosberg produced a lap time of 1 minute 37.5 seconds, with Thursday's leader Kevin Magnussen of McLaren next best.
Overnight rain meant the drivers started the day with wet tyres but, as the track dried out, they switched to intermediates.
Several teams have struggled so far this week with new technical regulations forcing a radical redesign of the cars and bringing new V6 turbo engines.
World champions Red Bull in particular have had difficulty with their new Renault engine although Australian Daniel Ricciardo at least completed several laps even if well off the pace of Rosberg.
Meanwhile, Formula One chief Bernie Ecclestone has criticised the new engine regulations in Formula One this season, branding them "a total farce".
Ecclestone was speaking to the English Daily Mail newspaper as teams begin testing in Spain for the new campaign.
"Look at the last few days. I said it was going to be like this - a total farce," he said. "They (the FIA and the teams) insisted on these new engines. If they wanted to race like this, they should go to Le Mans.
"The whole thing with the new engines is totally absurd. People want noise - something special, that's what F1 is all about - and now we have quiet engines and nobody on the track," he added.
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