The Spaniard was testing just a day after claiming a bitter third place in the Spanish Grand Prix, having been hit by Marc Marquez on the final corner of the last lap.
While he refused to comment on the incident post-race, he did concede that Yamaha needed to improve after Honda claimed its second successive one-two finish.
"I tried to ride perfectly, and I was risking so much," he said in the aftermath of the race.
"We just need to improve the bike. When we [do that] we can win more times."
A seamless gearbox remains Yamaha's priority in terms of development, but while its introduction still remains uncertain, Lorenzo said the day of testing did help establish other areas of progress.
"It [was] a long day [and] not easy to finish because after three days full of stress of competition the only thing you want is to rest," he said.
"I think the work was worth it because we improved some things.
"We tried many starts and finally I found again the same feeling I had last year. We improved the start, which is important for the next few races.
"I think we also improved the bike and I think we decided the new chassis. The one we choose is more stable in acceleration, so for this it has been a positive day."
Team-mate Valentino Rossi said Yamaha's 2013 frame was still a long way from being the obvious choice.
The Italian had also tested the frame in the final pre-season test but opted to start the season on the 'standard' YZR-M1.
"It was important to try to understand the new chassis," Rossi said.
"We made a lot of comparisons between the two but at the end more or less the performance is very similar.
"In some places it's better and some places it's worse. We will decide next week what we will use in Le Mans."