Stoner rules practice

A torrential storm, which had washed out the 125cc session beforehand, blew over by the time the premier-class hour began.

However it was not until the second half of the session that slick tyres could be used on the drying surface.

The change had an instant effect, dropping lap-times from a best of a minute, 32 seconds on wets to 1:24 within 10 minutes of the switch to the softer compound slicks.

The constant stream of improvements at the front - by the likes of Nicky Hayden, Andrea Dovizioso, Dani Pedrosa, Stoner, Randy de Puniet and Valentino Rossi - finally came to a halt with Stoner's 1:22.779, set with eight minutes to go.

Stoner, diagnosed with gastritis and mild anaemia after a series of medical tests following Laguna Seca, starts this weekend's ninth round 16 points behind World Championship leader Rossi.

Surprise US GP winner Dani Pedrosa, who lost the race and standings lead when he crashed in last year's wet Sachsenring race, got closest to Stoner in practice with 1:23.034.

Pedrosa, like Repsol Honda team-mate Dovizioso - ninth fastest - was due to try a new engine during the session, featuring a more user-friendly power delivery.

Rossi completed a top three covered by 0.309s for Fiat Yamaha, with De Puniet the top satellite rider in fourth for LCR Honda, just ahead of fellow customer RC212V rider Alex de Angelis (San Carlo Honda Gresini). De Angelis scored a joint career-best fourth at the Sachsenring last season.

Colin Edwards began his weekend with sixth for Yamaha Tech 3, with Toni Elias seventh and Hayden eighth. The American, who claimed a Ducati-best fifth last time out in his home race, led most of the wet part of the session and continued that form after the change to slicks before dropping back in the closing stages.

Hayate's Marco Melandri also led the timesheets in the wet before being ranked 10th in the dry.

Second in the championship Jorge Lorenzo, riding with foot and shoulder injuries sustained during a huge US GP qualifying crash, was only 11th quickest - but just 0.717s behind Stoner - with Loris Capirossi the lead Suzuki in 12th.

Capirossi's team-mate Chris Vermeulen limped away from a big highside near the end of the session. The accident occurred when the Australian rode through a stream of water on the exit of turn one, causing a big rear wheel slide that finally pitched him into the air. Vermeulen finished 16th.

MotoGP rookie Mika Kallio, returning after a one-race absence caused by a finger injury at Assen, was 13th fastest and the first rider over a second behind Stoner. As well as Vermeulen, the Pramac Ducati pilot was ahead of Tech 3's James Toseland, his team-mate Niccolo Canepa and Scot Honda's Gabor Talmacsi.

The MotoGP grid has been reduced to 17 permanent riders from Germany onwards, following the departure of the Grupo Francisco Hernando team, which had been running Sete Gibernau.

Mixed weather is expected to continue throughout the weekend.