Red Bull downplays reliability worries despite troubled last day of testing

The reigning world champion introduced its latest update package for the final two days at the Circuit de Catalunya, but it did not complete the kind of mileage that it had hoped for.

On the final day, a gearbox problem on the RB8 meant Sebastian Vettel was only able to do 23 laps as a number of rivals were able to complete race distances.

But although Vettel himself rated the team's winter testing programme as 'happier than 5 [out of 10] and less than 10 - something in between', Horner seems more upbeat.

"It has been a respectable winter for us to be honest," he told AUTOSPORT. "We pushed hard through that first test. We have ticked most of the boxes that we wanted to, and that is the thing with the way testing is constructed. You are doing your dirty washing in public on many occasions.

"I think it has been constructive. Looking back to 12 months ago when we were faced with a lot of KERS issues and so on, I think it has been a positive winter testing period.

"I don't think there is anything too different from the last couple of years. Certainly last year was tougher because KERS was a bigger issue and we ended up not running at the first race, but 12 months on KERS has hardly been mentioned this year."

Although many rival teams believe that Red Bull Racing remains the team to beat for the start of the campaign, Horner says he remains unsure about its chances.

"It is so difficult to tell. We have been trying to focus on our own programme, learn about the tyres and learn about the car. We will see in two weeks where the starting order for the season is, and that will no doubt fluctuate as there will be a development race for sure throughout the year.

"Whilst on paper we had a totally dominant year last year, it was obviously fairly tight on numerous occasions last year, even at the first race with McLaren. So it is difficult to say. Until we go to the first race, it will be impossible to say who is where. We hope to be competitive, and I think both drivers are in good shape - but Ferrari, McLaren and Mercedes, you cannot underestimate them."