Mar.23 (GMM) Championship leader Jenson Button has admitted he is impressed with Sauber.
But not far behind the leading pack, the Briton argues, is the former BMW outfit from Hinwil, Switzerland.
"They have definitely impressed me," Button is quoted by Die Welt newspaper. "They are very, very fast."
Team boss Peter Sauber agrees: "We went into the season with great expectations. Now we know that we have a fast car."