Andrea Dovizioso's promising pre-season preparations took a knock on the final day of the second Sepang MotoGP test, when the Italian suffered mysterious front-end problems during a race simulation.

Fourth fastest overall - behind fellow factory RCV riders Casey Stoner, Dani Pedrosa and Marco Simoncelli - after a soft tyre morning lap, Dovizioso then joined the trio in trying a longer run in the afternoon.

But he was in for an unpleasant surprise.

"The good point is that we are very fast. And to make the first two tests of the year fast like this is a dream. Also when we tried the race simulation we were fast, which confirms we are strong and have the possibility to fight this year," he began.

"But where I can't be happy is when we tried to do the race simulation and a problem with the front appeared, like in 2010 and some races in 2009."

After two fast laps, of 2min 1.3sec and 2min 1.4sec, Dovizioso suddenly lost half a second on his next lap - and never got it back.

"After three laps I lost grip in the front in the middle of the corner, closing [folding the front] many times, and after six laps it also happened when braking on an angle.

"After that I couldn't brake hard, as in the previous days here, and I couldn't be fast in the middle of the corner.

"I also needed to use sliding to exit the corner and on this track that is impossible because you finish the tyre. My lap time went slower, and slower and slower."

Towards the end of the 15-lap race simulation, Dovizioso's pace had dropped to a worst of 2min 2.772sec.

"I am coming out of this test very happy, but this [problem] confirms we are not perfect," he repeated. "It is something very strange and when it happens you can't do anything.

"We need to study exactly what happened. What we changed. For example, today we just put five litres more fuel. I don't want to say that is the cause, because the engineers need to study everything.

"But it looks like at the beginning of the race simulation I tried to push hard, like when I went for the best [soft tyre] lap time. I braked at the same point, because the bike is really stable now, but with five litres more I couldn't stop quite the same.

"So I arrived in the middle of the corner with a bit more speed and put much more 'shock' [load] on the front tyre. It looks like this might have made the tyre temperature go too high, too soon.

"That, maybe, caused this big problem, because after it stayed and I can't do anything, except go slow. I can't brake hard, can't be fast in the middle of the corner or turn. It was impossible to ride the bike fast like this.

"Maybe what happened in the first few laps hurt the potential of the tyre. This is our idea but we are not sure. We spoke with Bridgestone and they have some ideas, but nobody knows exactly.

"At the Qatar test we will start with full tanks and try to get that front feeling again so we can try to do something about it, because for it to happen in a race is the worst moment."

Without the front-end troubles, Dovizioso believes he could have been much closer to the race pace of team-mate Casey Stoner, who led all three days at the second Malaysian test.

"Even with this big problem, I made many laps in 2min 1sec," he said. "We are really fast compared with last year and I'm really happy about that.

"Casey is, for sure, in a better situation to everybody, with both the fastest lap and pace. But I think if I didn't have the problem with the front I could do a similar pace to him.

"I did a 2min 1.3sec on the second fast lap [of the simulation], but without pushing 100 percent. Casey's best lap was 2min 0.8sec. So not too far, but he was able to keep near that lap time for nearly all the simulation," concluded Dovizioso, who was fifth in last year's world championship.

During the pair of (three-day) Sepang tests, Dovizioso was classified 8th, 4th, 4th, and then 5th, 3rd and 4th.

The third and final pre-season test takes place at Qatar in mid-March.