The final day of official World Series by Renault testing at Motorland Aragon saw all teams devote themselves 100 per cent to testing in the new light aero configuration, with Estonian Sten Pentus proving fastest of all for Fortec Motorsport.

Pentus grabbed the best time in each session, running with the mandated smaller rear wing, a maximum permissible steering lock angle and no aero skirts, and finishing the day ahead of regular pacesetter Jean-Eric Vergne (SG Formula), with Brendon Hartley (Tech 1 Racing) making a welcome appearance in the top three when times from the two days of action were concluded.

The drivers spent the first hour getting their bearings and gauging the behaviour of their cars. Some teams had already done some winter testing with the light configuration, but this was the first time everyone had run the set-up at the same time. After a tentative first hour, Vergne got into action with new tyres and took advantage of perfect track conditions and a favourable wind on the straight to pull off an exceptional 1min 42.919secs. In so doing, he beat the series track record, then beat it again with a lap of 1min 42.908secs, before Nathanael Berthon followed the recipe of new tyres, new lap record.

With a lap at 1min 42.893secs, Berthon took over the top spot, but the order shifted again at the end of the morning, with Pentus creating the biggest surprise. The Estonian lapped in 1min 42.780secs, then went quicker still at 1min 42.390secs, allowing him to end the morning at the top of the timesheets ahead of Berthon, Vergne and Mikhail Aleshin (Carlin).

"Over a lap, the light aerodynamic configuration can actually be very quick, especially today with this favourable wind," Berthon revealed, "But the car slides more, and that's going to be difficult over a full race. We'll have to be very careful to avoid errors, particularly with the quicker tyre wear."

In the afternoon, the drivers put together series of laps to gather data on the new aero definition under race conditions and, from the outset, Stefano Coletti (Comtec Racing) showed a good turn of pace to take the lead ahead of Nelson Panciatici (Junior Lotus Racing) and Comtec team-mate Greg Mansell. Then Hartley and Walter Grubmuller took over, before Filip Salaquarda (ISR) donned new tyres with half an hour remaining, and made his bid for top spot with a lap of 1min 42.930secs, only to see Hartley go faster in 1min 42.777secs, moments before Julian Leal (International Draco Racing) created a red flag incident.

"We've made quite a few changes to the car since yesterday and we've made a lot of progress," Hartley reported, "This has been a good day for me, a great way to set us up for the season. On a track like this, the light aero set-up is effective, because there's plenty of grip on the circuit - but it won't be like this everywhere."

The last quarter of an hour was to see more changes in the hierarchy but, as in the morning, it was Pentus who got the better of his rivals, lapping in 1min 42.560secs, followed by Vergne and Hartley, before the Kiwi spun off looking for an improvement on his last attempt.

"We did a lot of work on the light aero set-up this winter and yesterday and maybe that's why we got the better of the others today," Pentus concluded, "Whatever the reason, it gives me a big hopes going into the first race. We need to work and work, but this kind of result is a real motivator."