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Ferrari are concerned that their failure to develop their car is affecting current World Championship leader Fernando Alonso's title bid.

Team boss Stefano Domenicali admitted on Friday that problems with the Ferrari wind tunnel meant that some of their planned updates had not worked.

"In the second part of the season, when trying to bring updates to the car, not all are working on track," he said.

"If you are not able to improve, it's more difficult to fight for the title."

Ferrari have discovered correlation problems between the data from their wind tunnel - a crucial tool in honing the aerodynamics of a Formula 1 car - and that from the car on the track.

It was a problem that initially became apparent at the start of last season following a switch to using a larger scale model and which Ferrari thought they had solved.

But it has recurred this summer, and the latest example was the introduction of a new rear wing at the last race in Singapore

Ferrari have been evaluating the new wing again on Friday's first practice day at this weekend's Japanese Grand Prix.

Domenicali said: "You try to improve the situation and when you are talking about a tool that is so significant for the development of the car you need to make sure it is at the top level of its performance. It seems that is not the case any more.

"So it is the time to work and see how we can improve that.

"It's part of the continuous improvement we have to do with the team but I don't want to hear that as an excuse not to deliver what is necessary to deliver on the track.

"We need to keep pushing to ensure Fernando will have the best car up to the end of the season."

Alonso is 29 points ahead of Red Bull's Sebastian Vettel but has not won a race since the German Grand Prix in July, five races ago.

Since then he has been fifth in Hungary, retired after being hit at the start in Belgium and taken third places in Italy and Singapore.

Not once this season has the Ferrari been quick enough to qualify on pole position this season in dry weather.

Domenicali said: "We cannot rely only being third or fourth, we need to make sure we can win a race and then we see what is the situation with the others."

He added that said Ferrari would take their own wind tunnel off-stream for a period at an unspecified time in the future to analyse what was wrong with it.

In the meantime they will use a wind tunnel at Toyota Motorsport's base in Cologne, Germany, to develop their car.

"We are using other facilities and in the next couple of weeks we will define a programme to be more specific on that, to see what is best time to shut down and improve things that are not at the maximum level at the moment," he said.