Ricciardo was seventh in the timesheets but believes understanding the STR8 was more important.
"A very productive day, testing various suspension options, which was very interesting and has provided us with plenty of data to look at," said Ricciardo.
"Therefore it was not a day for the time sheets, but one during which we learned a lot."
Ricciardo completed 70 laps at the home of the Spanish Grand Prix and added that evaluating the Pirelli tyres is crucial.
"It’s been interesting evaluating the Pirelli tyres, which have different characteristics to those from last year, but we will need some higher temperatures before we get an accurate picture of how they perform. Now it’s down to Jean-Eric [Vergne] to carry on for the next couple of days, before I get my final two days of testing when we come back here in just over one week."