Marcus Ericsson has denied claims that Sauber's flying pace in Jerez was due to glory runs, adamant there is more pace to come.
Despite failing to score a single point last season in a slow and heavy C33, Sauber have been right up there on the timesheets in pre-season testing.
Behind the wheel of the new C34, Ericsson and his team-mate Felipe Nasr were inside the top two on all four days at Jerez including Nasr setting the pace on Day Three.
This has led to some speculation that Sauber have been going for low-fuel glory runs.
Ericsson, however, insists Sauber have yet to show their true pace.
The Swedish racer told Autosport: "We have quite a bit of margin, to be honest, so that's positive.
"We've had a really good test. It's been very positive that every day we've done a lot of laps and we've had no real issues with the car.
"And it was interesting for me driving on day one and day four to see the progress we've already started to make.
"The car I drove on Sunday to the car I drove this afternoon is quite a few steps on in feeling."
He explained that the new car is a massive step up on its predecessors as Sauber have managed to negate all the C33's flaws.
"Compared to the car I tested in Abu Dhabi, we have improved," he said. "I think the car has made progress. It's a better car this year.
"It's more stable in general, and under braking and through the corners it gives the driver more confidence.
"Also I think Ferrari have made a good step on the power unit compared to the one I drove in Abu Dhabi. But still we have to wait and see what others have got."