Montoya quits turbulent formula one career for a return to oval racing

Juan Pablo Montoya stunned the grand prix world yesterday by announcing that he will abandon his formula one career at the end of the season and switch to the US-based Nascar oval stock car racing Nextel Cup series for 2007.

The 30-year-old Colombian will join forces with the Indianapolis-based Chip Ganassi team at the wheel of whose IRL car he won the 2000 Indy 500 classic before moving into formula one with the Williams squad the following year.

Montoya, who won four grands prix for Williams, switched to McLaren-Mercedes at the start of last season and has won three more victories for the Woking-based team. He originally graduated to formula one with Williams in 2001 as replacement for Jenson Button, who had made his debut the previous season before moving to Benetton.

Last year Montoya proved that he could be a match for his team-mate Kimi Raikkonen when he was on form but this year he seemed to lose consistency and motivation and his relationship with McLaren has become strained.

Ganassi recently admitted that he would be keen on re-signing Montoya but it had been thought that this was for his IRL outfit of which the British driver Dan Wheldon is currently a member. However, it emerged that talks between the driver and his former team chief have focused on a move to NASCAR, with Chip Ganassi Racing looking for a replacement for Casey Mears.

That Montoya was a volatile personality was never in any doubt. At the 2003 French grand prix he lost his temper with the Williams crew on the pit wall after concluding - incorrectly - that their refuelling strategy had favoured his team-mate Ralf Schumacher, who went on to beat him to the race victory.

Harsh words were subsequently exchanged and Montoya signed a McLaren contract the following week even though his Williams deal still had 18 months to run. It was a classic example of the Colombian driver's unpredictable streak which McLaren believed they were best capable of handling, even though events have proved otherwise.

"Juan is a passionate character and sometimes this means he makes impulsive decisions which lead him to impulsive conclusions," said Patrick Head, the Williams technical director, after the French grand prix row. "Once he had made his decision [to leave] that was that." He added: "In France [in 2003] he went into a sulk and we couldn't have a situation where he accused the team of being incompetent. I felt this was not something we could say nothing about."

Yesterday Sir Frank Williams admitted it was a shame that Montoya would be quitting the formula one scene. "Juan is a feisty and very determined driver," he said, "and when he was really on form his overtaking ability was outstanding. But he always liked racing in the USA and in a sense this decision means that he's returning home."

McLaren are expected to make a statement today.