Monday, 9 November 2009, 10:57 GMT

Valentino Rossi believes that mid-season changes to MotoGP's engine regulations affected Yamaha far more than rivals Ducati and Honda.

Ahead of the Czech Grand Prix in August, riders were limited to using seven engines each over the final seven races of the season, putting a premium on reliability.

The seven-time world champion believes that this pegged back Yamaha's advantage in the engine department whereas others were able to gain from it.

"Since Brno, we started to struggle more," said Rossi. "Before then our bike was the most balanced, but also very quick in a straight line, while from Brno our bike has stayed well-balanced, but we lose six or seven kph to Ducati and Honda.

"We have been the most disadvantaged ones. We've won a lot less since Brno. We know what to concentrate on next year, when we'll have even fewer engines."

Rossi said that, perhaps because of this, his 2009 world title was the hardest won of his career, such has been the pressure exerted on him by his team-mate Jorge Lorenzo, Honda's Dani Pedrosa and Ducati's former world champion Casey Stoner.

"In the end, I won 'only' six races, but that's because there were four of us doing the winning," he added.

"But I won six races - more than anyone else, had seven poles - more than anyone else, and I passed the 300-point mark, so it's been a great season and we're going home with a good overall result."