Although the 2009 MotoGP and 125GP titles have already been decided, this weekend's Valencia season finale will still feature one championship showdown - between Hiroshi Aoyama and Marco Simoncelli in the 250cc class.

Scot Honda rider Aoyama will start the event 21 points clear of Metis Gilera's reigning champion Simoncelli.

Since Valencia became the final race of the year in 2002 there have been six previous occasions when the world title has been decided at the event:

MotoGP class:
2006 - Valentino Rossi (Yamaha) had an eight point advantage over Nicky Hayden (Honda) arriving at Valencia for the final race of the year.

Rossi looked set to take his sixth title in a row after qualifying on pole, with Hayden down in fifth place on the grid. However Hayden made a great start and was up to second behind Troy Bayliss after just 3 laps.

Meanwhile Rossi had made a less convincing getaway and was only seventh on the fifth lap, when he crashed and re-started in last place. Although Rossi managed to fight his way through to 13th by the flag, Hayden did enough by finishing third to win the title.

This is the only occasion that a rider going into the final race at Valencia leading the championship has failed to take the title.

250cc class:
2003 - Starting the race at Valencia, Manuel Poggiali (Aprilia) had a seven point advantage over Roberto Rolfo (Honda). Rolfo was never in the hunt and Poggiali cruised to a comfortable third place finish to become 250cc world champion in his first season in the class.

2006 - Jorge Lorenzo (Aprilia) had a thirteen point advantage over Andrea Dovizioso (Honda) arriving at Valencia for the final event of the year. He did enough by finishing fourth to clinch the title, with Dovizioso finishing seventh after he had been leading Lorenzo early in the race.

125cc class:
2002 - Manuel Poggiali (Gilera) had a chance of taking the title at the final race of the year at Valencia; he had an eight-point deficit to Arnaud Vincent (Aprilia). However, Vincent finished second to become the first French rider to win the 125cc world title.

2005 - Mika Kallio (KTM) needed to win the race at Valencia to take the title with Thomas Luthi (Honda) finishing lower than 13th. Although Kallio did as required in winning the race, Honda rider Luthi took the title by cruising home for a ninth place finish.

2007 - Gabor Talmacsi (Aprilia) had a ten-point advantage over team-mate Hector Faubel at the start of the Valencia race. The two riders took the top two places on the grid and Faubel won a fantastic race in which the top five riders crossed the line covered by less than a second; however Talmacsi did enough to take the title by finishing second.