Valentino Rossi believes the cancellation of second practice at Aragon will prove particularly painful to Ducati because it is trying to fine-tune the latest version of its 2011 bike this weekend.

The struggling team has introduced a part-aluminum frame for the Spanish event, having tried it on the 1000cc version of the bike during its latest 2012 rules test at Mugello.

Rossi was eighth fastest on the revised bike this morning and has committed to sticking with it for the rest of the weekend. But he rued the loss of afternoon practice to a series of power failures at the circuit, saying it would cost Ducati essential learning time.

"Everybody is at some kind of disadvantage to lose the time this afternoon, but more for us because we have to better understand the different settings of the bike," he said.

Saturday morning practice has been extended to 75 minutes to make up for some of the lost running, but Rossi does not think this will totally solve the problem.

"For sure, one longer practice is worse than two short practices, especially for working on the bike," he said. "But we can understand it better tomorrow and we'll continue with the aluminum frame."

He was cautiously optimistic about the potential of the updated bike – saying it was definitely a step forward even if it was unlikely to launch Ducati right into contention.

"Our potential was nothing special this morning but the feeling was not so bad," said Rossi.

"For me, the first impression was like in Mugello – we improved the bike on change of direction. It had a bit of understeer but on front feeling it was not so bad. It looks like a small step, but we have to understand it more clearly tomorrow."

Rossi was 1.395sec away from pacesetter Dani Pedrosa's Honda, but content to be within 0.5-0.7sec of fourth- and fifth-placed Marco Simoncelli and Andrea Dovizioso.

"We hope that tomorrow we can be closer because the difference, especially to Dani, remains huge. But we are not so far from Dovi and Simoncelli," he said.