British 125GP winner Scott Redding clocked the third fastest time on an opening day of testing in Valencia hit by wet weather conditions.
Redding, who made his debut on Aprilia's new 2009 factory machine in Jerez earlier this week, completed only 37 laps on his way to posting a best time of 1.54.217.
That was 1.2s slower than Aspar Aprilia rider Julian Simon, who continued his sensational start to 2009 by clocking the best time.
Simon has now topped all four days of testing so far in 2009 having dominated the Jerez session previously. Blusens Aprilia rider Redding was only 0.6s off the second best time of Spaniard Esteve Rabat.
Having finished second in the Jerez test to get his 2009 pre-season preparations off to an impressive start, Bradley Smith decided not to venture out on track at all because of the conditions.
1 Julian Simon Aprilia 1.53.082
2 Esteve Rabat Aprilia 1.53.696
3 Scott Redding Aprilia 1.54.217
4 Luca Vitali Aprila 1.55.535
5 Joan Zarco Aprilia 1.57.106
6 Marc Marquez KTM 2.01.194
7 Cameron Beaubier KTM 2.01.841