Caterham drivers Charles Pic, Giedo van der Garde and reserve Heikki Kovalainen believe the balance of the CT03 has been improved after a raft of upgrades was fitted to the car in Barcelona.
Van der Garde reckons the main area of progress now needs to be focus on corner entry.
"The car had good balance on the medium tyres, both on short and long runs, and I think we showed quite good pace on that compound and on the hards but we need to work on the car's behaviour on the entry into corners," said the Dutchman. "Against that is the fact that the car has much better traction out of the corners and that's a really positive sign."
Pic sat out FP1 but was also positive regarding the changes.
"On the first couple of runs the car had too much understeer in the low and medium speed corners so we made a couple of mechanical adjustments and the balance started to improve on runs three and four," said Pic. "Tyre degradation was also not too bad on either compound, but we have more work to do on bringing the tyres up to temperature so we can get them working efficiently as soon as possible."
Kovalainen's FP1 run was limited courtesy of a mechanical issue, but added "the balance has been improved, especially mid-corner and in both low and high speed turns, so it's easier to push."