Heidfeld realistic about BMW's prospects

The German has been the main threat to the top two teams so far this season, and his charge to fourth place in Bahrain included a daring overtaking move past world champion Fernando Alonso.

But despite the impressive progress that BMW have made over the winter, Heidfeld is not underestimating the difficulties that lie ahead in trying to match the rate of development of the two leading outfits.

"That is something I am very curious to find out," he told autosport.com.

"The progress we have made in the last two years and also over the winter has been very good.

"And in the last season we actually made a big improvement from mid-season until the end, so if we can keep that up then it will be great.

"But the opposition now is different. Here we are dealing with Ferrari and McLaren. This is a different ballgame altogether. They are proper big boys. But of course it is exciting to find out how well we do."

With poor weather hampering testing in Barcelona this week, and new parts being readied in time for next week's Spanish Grand Prix, Heidfeld thinks it is too early to predict how strong BMW Sauber will be for the next race.

"We are expecting more parts to come just before the race, so it is an ongoing process for us. I really don't know how it will be at the moment."

The other uncertainty for Heidfeld is his contractual position, with his deal with BMW Sauber coming to an end this season.

However, after BMW motorsport director Mario Theissen made it clear that he sees no reason for change if Heidfeld continues to impress, the man himself is upbeat about securing a contract extension.

"There's no news at the moment, but I am pretty confident," said Heidfeld about his 2008 plans.

"Like Mario officially said, there should not be any big change in the future. So we will see."