Reigning double MotoGP champion Casey Stoner took his 40th grand prix pole in qualifying at Catalunya on Saturday, ahead of what could be one of the most hard-to-predict races of the season.

Stoner, Repsol Honda team-mate Dani Pedrosa and Yamaha's title leader Jorge Lorenzo have filled all but one of the podium places in the four events so far this year.

However potential differences in rear tyre choice and a heavy rate of degradation mean fellow top six starters Cal Crutchlow, Andrea Dovizioso and Ben Spies could also feature at the front during the grand prix.

And that's without taking into account the weather, which has been scorching hot for the past two days, but with an outside chance of rain for the race.

Small wonder Stoner, who has been concentrating on the harder option tyre but is also yet to make a final decision, is taking nothing for granted.

"So far we've done quite a lot on the hard tyre, quite a bit more than other people, and we feel quite confident with the pace," said Stoner, who took pole by 0.146s over Lorenzo.

"Everyone else seemed to put a few more laps on the soft tyre. It's a slight risk for tomorrow in warmer conditions, but if the conditions cool down there is every chance we can go to soft as well.

"I think this is going to be one of the first races in quite a long time where tyres may be quite critical, especially towards the end of the race.

"We haven't seen that very often with Bridgestone tyres, but if the extreme temperatures continue tomorrow there is every chance the tyres could get a little too high for too long."

Stoner also worked on improving the ongoing chatter problems with his RC213V.

"We were in and out a lot during the session trying a few different things, hoping to reduce the chatter which is still proving to be a problem.

"As soon as I touch the throttle the bike starts to chatter in the rear and it's making things very difficult. Towards the end of the session we managed to improve it slightly but I think we need to make another step before the race.

"Tomorrow, for sure tyre degradation is going to play a role so we're going to have to wait and see but I'm happy to start from pole".

Bridgestone's Shinji Aoki believes that a lot of riders will chose the softer option rear, should the race be dry, meaning the closing laps could be especially challenging.

"In this morning's free practice session some teams did long runs on the softer rear slick tyre to evaluate its performance for race distance and I believe this option will be widely used tomorrow, though there is a chance of rain tomorrow as well," he confirmed.

"I expect all riders to use the harder front slick for the race with the majority of the field opting for this compound in the new specification front slick tyre as this was a common choice in qualifying."

Tech 3 Yamaha's Crutchlow will complete Sunday's front row, followed by Spies (Yamaha), Pedrosa and Dovizioso (Tech 3) on row two.

Factory Ducati riders Nicky Hayden and Valentino Rossi will line-up on row three and could both be podium contenders in the wet.

Lorenzo starts round five with an eight point lead over Stoner.