Ducati MotoGP stars Valentino Rossi and Nicky Hayden worked on 'various configurations of the chassis, engine and electronics' during the start of a private test at Mugello on Thursday.

With the planned Estoril post-race test abandoned due to poor weather, this week's test is due to mark the first chance for the factory race riders to try a series of development parts for the Desmosedici GP12.

Those developments include a new smoother engine aimed at improving corner exit characteristics, although Ducati did not do into detail about Thursday's schedule.

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The factory did reveal that morning rain kept both riders in the pits until 2pm, by which time the track had dried and that both riders then rode until around 6:15pm.

The Ducati statement added:

'They [Rossi and Hayden] were looked after by their respective teams, headed by Jeremy Burgess and Juan Martinez and by Team Manager Vittoriano Guareschi. Test rider Franco Battaini and the Ducati Test Team, headed by Filippo Preziosi, were also present, having started on Tuesday.

'Valentino Rossi completed 55 laps, Nicky Hayden 52, as they began their work on various configurations of the chassis, engine and electronics. The weather forecasts for tomorrow's final day are favourable.'

No lap times were released but one of Rossi's mechanics, Alex Briggs, wrote on Twitter (@Alex__Briggs): "I can't tell you exactly what we did. But it's been good. Some stuff not what we need, but we also tested something that made us smile."

He added: "Best thing is that we found a setting that worked well quickly. This means our base from Portugal [and used at Le Mans] is solid."

This week's test is the first of three planned for Ducati at Mugello during May, June and July. May and June are private tests, while July will be a post-race test following the Italian Grand Prix.

The new Ducati parts are due to be introduced from the Silverstone (June 17) round onwards, although the limit on MotoGP engine changes means the full upgrade package is not expected to be available until Laguna Seca (July 29).

Rossi took his best finish as a Ducati rider with a wet second place in Sunday's French Grand Prix at Le Mans. However Rossi and Hayden remain significantly behind the leading Honda and Yamaha riders in the dry.

Former World Superbike champion and MotoGP race winner Troy Bayliss is also present at Mugello this week, where he is testing the 1199 Panigale Superbike.