Valentino Rossi may have failed to better his day one time during testing at Sepang on Wednesday, but the Fiat Yamaha star still kept the number one position by almost half a second.

The Italian, who turns 29 in ten days time, was just 0.172secs slower on a qualifying tyre than his mighty 2mins 0.300secs Tuesday time, while managing to fractionally improve his race tyre pace to a 2mins 1.371secs.

The quickest winter race-tyre lap is a 2mins 0.964secs, set by world champion Casey Stoner in late January.

"Today was another very good day and I had a good pace and rhythm all day. We tested some different Bridgestone tyres before again trying the one I prefer, which confirmed that this is the best one for us and so we will use it for the long run tomorrow," said Rossi.

"We worked a little bit on the suspension and also on the electronic mapping and we also tried a lot of practice starts, maybe as many as ten, and we need to improve a bit in this area.

"I also tried a new cowling which is aimed at improving the cooling system and this had a good result. Finally I tried a qualifying tyre again and, although I made a small mistake on my lap because I was quite tired by then, it was again very positive," he concluded.

Repsol Honda's Nicky Hayden was once again Rossi's closest challenger - amongst the slim nine-rider field present - the American putting his Repsol Honda 0.428secs from Rossi after a qualifying tyre lap of his own. Nevertheless, Hayden will be disappointed to have lapped over half a second slower than his qualifying tyre best at January's test.

As planned, Hayden and Repsol Honda brought an end to their Sepang test on Wednesday evening, leaving an eight rider line-up for the third and final day.

A 1.1secs gap separated Hayden from Gresini Honda rider Shinya Nakano on Wednesday, with Rossi's Michelin-shod Fiat Yamaha team-mate Jorge Lorenzo fifth - but the only full-time rider to set his best time on a race tyre.

Rossi's best race tyre lap was a 2min 1.371secs, Hayden's a 2mins 2.309secs, Nakano's a 2mins 2.539secs and Alex de Angelis' a 2mins 3.029secs.

The Kawasaki and Yamaha test teams once again completed the field.