Fiat Yamaha's Valentino Rossi was one of several riders who voiced concern over track conditions during the night at the Losail International Circuit, site of Sunday's season-opening Qatar Grand Prix.As the defending MotoGP World Champion embarks on the quest for a 10th World Championship, he said that the later it gets, the worse the track. And he added that the conditions in qualifying will be critical in making race day decisions."Yes, last year was a different story because on Sunday it rained and we raced on Monday, but we raced at 9 o'clock, so it was two hours before," he said of last year's postponed race. "We check in the test that after 10:00 the humidity, also before, the humidity growing up very quickly and especially the second day in the test had a lot of crashes in the turn two, that is maybe the worst part of the track in the bad conditions. So waiting until 11, I think, is a little bit risky."Because race time temperature should be in the mid-70s, it won't be critical. The problem comes with the 80 percent humidity."So with our bike, with a lot weight and speed in the corners, we suffer a bit these conditions," Rossi said. "We see also the condition at 11 o'clock and try to understand and decide for the race."Surrounded by younger riders at the pre-race press conference, Rossi said he was still motivated as he enters his 15th full season in the World Championships."Yes, the first motivation is always great rivals. Try to beat the other guys," he said while seated between Casey Stoner and Andrea Dovizioso. "In these last two seasons we enjoy a lot. Have some great battles and on the paper, also this year will be the same, because all the other top riders are in a good shape with a good performance in the test. We have some new guys arriving from 250 and Superbike, so will be funny."The team has improved the YZF-M1 throughout testing, much of which involved getting better feeling with the new long-life engines."We try to modify also something in the weight, in the chassis for a better grip and the bike work very well in Sepang and Qatar," he said. "So this is positive, because especially here in Qatar last year we had some problem and this time I think it's possible to make a bit better."Ducati Marlboro's Stoner is one of the riders expected to challenge Rossi's dominance this year, and especially here in the desert. Repsol Honda's Dani Pedrosa has had a disastrous testing season and Rossi's teammate Jorge Lorenzo has a damaged right hand."I made a lot of podiums and won the last race and I was consistently at the top, but we changed to Ohlins and right now I can't find the feeling," Pedrosa said. "That's why the winter was not good and quite difficult."Lorenzo said that "the problem is when I brake, the pressure I have to make with the hand causes me a little bit of pain. We'll see if I can brake as normal."The only rider on Rossi's level is Stoner, who continued an unenviable streak by crashing in turn two at during the Losail test each of the past three years, "along with almost half of dozen other riders each time, so it's quite strange. There's a few points that catch people out."Part of that is because of the humidity, he said. "In general, the track at nighttime's been very good; it's up until about 10-11 o'clock and then things start to change."Yeah, in general we've had very good success here. I don't really know why. Maybe it's because the track's a little dirtier, a little slipperier and it suits my style better. But yeah we'll be going into this season the same as we have in the past and we'll just see what we can do on Sunday. And as long as I come out with decent points I'll be happy."Pedrosa's teammate, Andrea Dovizioso, was also worried about the conditions."The humidity is a bit dangerous because is not so easy to manage and we can't push like at 10 o'clock or 9 o'clock, so we need to see the situation how it will be," he said. "But for everybody will be the same."