Sauber won't be making first use of their new passive DRS system this weekend after all, following the time lost due to wet weather on Friday morning that cost them a significant proportion of their testing and development track time.

"We performed a lot of tests on some new parts and the [passive DRS] system actually performed better than we were expecting," said Tom McCullough, Sauber's head of track engineering. "It's still not at the stage where we think we're going to race it, even though we [were] pretty tempted."

Rivals Lotus - who are further along with the development of their own passive DRS system - had already ruled out use of the system at Spa.

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Drivers Nico H?lkenberg and Esteban Guti?rrez both admitted that the weather had left them struggling to get through the planned programme of testing on Friday and both seemed distinctly unhappy with how their preparations for the Belgian Grand Prix stood overnight on Friday.

"It was quite a tricky day with the mixed weather conditions this morning. We couldn't really get a full run on slicks," said H?lkenberg. "I think there is still room for improvement. We still have some work to do on the set-up, as things can and have to be improved. I wasn't happy with the balance of the car."

"In the morning we had some running on a track that was wet and damp," added Guti?rrez. "We were able to run some aero tests, but, unfortunately, we didn't get through the whole programme.

"The qualifying simulation in the afternoon was not good," he continued. "I lost part of the diffusor at the beginning of FP2, which impacted on performance. I'm not feeling very comfortable with the car. It's tricky driving the car on relatively low downforce, and the balance is not quite right."

McCullough, however, was taking a more upbeat view of how things were going for the team at Sa-Francorchamps.

"The rain that was forecast prior to FP1 gave us some practice in those conditions, which could well be useful later in the weekend," he insisted, while conceding that neither driver had been happy with ca's balance in the dry running during the afternoon. "We definitely have some work to do tonight in order to improve that," he said.

In McCullough's eyes, the passive DRS is more of a long-distance project with the main focus being developing for the 2014 season when the F1 technical specifications are extensively overhauled.

"With regards to next year, any system that you can use to help reduce drag will always help you, so yes, it is part of the consideration for next year's car," he said on Friday afternoon. "Overall this project is making progress and we will decide [overnight wheather we will use it for the race on Sunday."

As for the rest of the team's 2014 plans, McCullough said that the current uncertainties hanging over the team with regard to its financial viability weren't being allowed to impact the team's preparations for meeting next year's new technical regulations.

"We started work on our car pretty early for 2014, mainly aerodynamically and then more and more during the year, working closely with our powertrain partner, developing that car," he said.

And while the current car "is coming to an end at the factory", the team continues to work on improving it with McCullough admitting that the team hadn't got off to the best start in 2013 and was determined to stop that from happening again next season.

"The start of this year wasn't as competitive as we wanted," he said. "Understanding that is key to making a good car next year, so a lot of the work we've been doing on the car is in conjunction with next year's car, so we couldn't just stop designing this year's car.

"We've worked very hard and we have made some good improvements. The update package we bought to Budapest, we were very happy with. We feel we're understanding the car a lot better now.

"This year's car, even though from a points point of view we were not scoring points and saw some of our direct competitors taking those points, in lap time we often weren't far away," he continued. "A small difference in lap time, different competitiveness from track to track, bringing improvements to the car... all of a sudden the points can come your way.

"I wish we'd started the year as we are now, but we feel confident for the second half of this season."