Romain Grosjean says the Lotus Formula 1 team is "miles off" where it expected to be after showing disappointing pace in free practice for the Bahrain Grand Prix.
Reliability problems have plagued the twin tusk E22 so far this season, but Lotus drivers Grosjean and Pastor Maldonado completed an encouraging 103 laps in Bahrain on Friday.
Their programme was disrupted only by a minor turbo issue for Grosjean and some floor damage after Maldonado launched off the Turn 4 exit kerb.
However, both driver languished near the bottom of the timesheets. Maldonado was quickest of the two but three seconds off the pace of Lewis Hamilton's Mercedes in each session.
Hamilton stays ahead in second practice
Hamilton puts Mercedes on top in FP1
Grosjean said the car was not delivering the performance the team expected now it appears to be reliable.
"We just need more time to understand why in the windtunnel the car looks good and on the track it's not as good as we hoped," he said.
"Mercedes has a bit of an advantage but we are miles off where we would like to be.
"Red Bull is maybe not the best example because they have an outstanding car, but Toro Rosso is far ahead of us and we should be capable of being in front of them.
"Today we were slow. I don't know if it's track related. I'm sure we could use the Pirelli tyres better. It's not the best weekend so far.
"We have seen we have a quite sensitive car to wind conditions and we are not yet exactly with our baseline set-up in the best region for aerodynamics. The engineers are looking into it."
Grosjean said he was still not comfortable driving the E22 and felt Lotus had taken a backward step from last weekend's encouraging run to 11th in the Malaysian Grand Prix.
"The car is quite difficult to drive at the moment, to be honest," Grosjean added. "The brake-by-wire is still not perfect, rear downforce is not the best strength right now. It just makes everything a little bit harder."
Team-mate Maldonado, who was fractionally quicker in each session, reckons Lotus will catch up to the other teams as it gains understanding of its car.
"The car is a bit slow but we need to work," he said. "The feeling I got in FP2 was quite good. There are many points to improve in the set-up especially, but we are moving in the right direction.
"We need to work harder than the other teams, but we have more room to improve than the others.
"We are three seconds from the front. One second, in my opinion, is easy to get. Hopefully we can fight with the Saubers, maybe slightly better. We will see."