Dani Pedrosa is scratching his head for a solution to the rear grip trouble that is hampering the Repsol Honda rider at the San Marino MotoGP.

Pedrosa, who trails team-mate Marc Marquez by 30 points in the title race, qualified on row two in fourth place, but felt his final position had been achieved with 'a bit of luck' due to the tyre issues he has encountered at the Marco Simoncelli circuit.

The Spanish rider - who suffered a small crash in FP3 - set a fastest time of 1m 33.726 seconds, leaving him 0.811s down on Marquez but only 0.153s behind Valentino Rossi, who grabbed the final place on the front row.

"We had a bit of luck to take fourth on the grid, because we have been having problems with all the rear tyres that we have used," said Pedrosa.

"In the morning it was OK, I crashed at the end but the feeling was good and I was doing a good rhythm, so for FP4 we didn't actually change much but I went out and suddenly there was no grip.

"I stopped after two laps and then went out again and had no grip so I complained and they changed the tyre again but again I had no grip and then FP4 was over.

"I waited for Q2 and went out and had no grip so after two or three laps I was pushing but over one second slower than my best and I don't understand it.

"I was quite nervous because I suddenly had no grip and the lap times at the top were as fast as usual. But at the last minute I put in a new tyre and I had normal grip so could jump to fourth position but couldn't really focus and I wasn't able to achieve my goal of the front row."

When pressed as to what had happened between the morning and afternoon session Pedrosa was at a loss to explain it other than thinking that there was an issue with the Bridgestone tyres.

"I had no grip for three tyres and then suddenly had grip so I think that there must be something on the tyres because I changed the bikes and I know the feeling of whether it is a tyre or a bike [causing the problem]. I used three tyres that didn't work and all were the soft compound. The front was sliding too but that's especially because when the rear tyre has no grip the front has even less.

"The tyres normally go together so once the rear tyre has grip the front feels better. My problem was that I couldn't open the throttle. I've spoken to Bridgestone and they said that the tyre was the same but for sure it didn't feel like that to me."