Hayden tops Jerez test, Rossi rides 2005 bike.

Repsol Honda's Nicky Hayden, third in Sunday's season opening Spanish Grand Prix at Jerez, has set the pace during Monday's test session at the same circuit.

Hayden set a best time of 1min 39.910secs on his factory Honda which, if set on race rubber, is well inside the official circuit record of 1min 40.596secs - set by Valentino Rossi back in 2005. The pace in Sunday's grand prix was significantly slower, with race winner Loris Capirossi leading the field with a 1min 41.248secs best.

Behind Nicky, Sete Gibernau - whose Desmosedici broke down while holding third early in Sunday's race - again underlined what might have been by finishing the day second fastest, on what were definitely race tyres, with Capirossi 0.3secs slower for third (also on race rubber).

Further back, Casey Stoner again impressed with the fourth fastest time - beating fellow Honda rookie Dani Pedrosa, runner-up on Sunday - while Tech 3 Yamaha's Carlos Checa shot up the order after a difficult race weekend with sixth on his Dunlop shod M1.

Meanwhile, having struggled with chatter problems during both the pre-season test at Jerez and for much of the grand prix - world champion Valentino Rossi and Camel Yamaha team-mate Colin Edwards spent Monday attempting to find a much needed solution to the vibration issue.

As part of that process Rossi - who qualified just ninth, then was brought down by Toni Elias at the first corner of Sunday's race before finishing 14th - also completed one run on the 2005 YZR-M1, in order to compare its performance with the 2006 bike.

The decision to test the old bike may have been triggered by the fact that Rossi qualified 0.741secs slower in this year's Spanish Grand Prix than in the 2005 edition, with his fastest 2006 race lap also some 1.588secs slower than his race winning best from last year.

The fastest race lap deficit is not so significant, as most riders - for whatever reason - went slower in this year's race, but the slower qualifying pace does underline the extent of the chatter problem, since Capirossi was able to set a new lap record (by 0.4secs) on Saturday, proving that track conditions were favourable.

Rossi and Edwards completed 72 and 76 laps respectively today and made 'some positive steps' towards understanding the cause of the speed-sapping vibration. However, Rossi still lapped one-second slower than Hayden for seventh on the timesheets, with Edwards - who qualified 10th and finished the race in 11th - only 13th fastest.

"After such a disappointing opening weekend to the season, it was important for us to have the chance to test today," explained team director Davide Brivio. "It was a very useful and interesting day for us and we were able to collect a lot of important information which we believe will help us. It was good to be able to go back to some of the settings that we tried over the weekend and to evaluate them in a more relaxed atmosphere, without the time pressure of a race weekend.

"In addition we decided to have Valentino ride the 2005 M1 for a few laps so we could compare its performance at this track with that of the new bike," he confirmed. "It was interesting to see the difference - a few things about the '05 bike are better at the moment, but overall it seems the '06 bike is still a more improved package and Valentino's fastest times today were on the 2006-spec M1. Anyway the data from this comparison should help us a lot as we continue to develop the new bike.

"Valentino was able to make some good improvements to the performance of the '06 bike so this is encouraging for Qatar. Colin's test wasn't quite as positive but after today we now have a better idea of what to do in order to bring him back to the level he was at in Barcelona. It's been an important day for us and now the Yamaha engineers will work hard to evaluate the data gathered so that we can come to Qatar and fight at the front with both riders where they belong," he concluded.

Round two of the 2006 MotoGP World Championship will take place in Qatar on April 8.