LONDON, England - The chassis used by Sebastian Vettel during the first four races of 2014 was bent, according to Germany's Auto Motor und Sport.The reigning quadruple World Champion notably struggled alongside team mate Daniel Ricciardo until the 2014 Spanish GP, where he spectacularly scythed through the field and declared for the first time that driving in 2014 is "fun".Although no obvious chassis flaw was found between the Chinese and Spanish grands prix, Red Bull nonetheless put Vettel at the wheel of the winter testing chassis in Barcelona.'CROOKED' CHASSISVettel said: "I do think it made a difference." Auto Motor und Sport correspondent Michael Schmidt said further investigations have been taking place at Milton Keynes after Barcelona.Schmidt confirmed: "The chassis (which Vettel named Suzie) he used in the first four races was in fact crooked."Schmidt said Vettel, the winner of the last nine grands prix of 2013 on the trot, had suspected something was wrong with his car after the 2014 Chinese GP."A second down (to Ricciardo) was too much. I had not forgotten how to drive," said Vettel.