Following a brake failure during the second day of testing at Jerez, 2008 World Champion Lewis Hamilton admitted Mercedes’s 2013 challenger still had key flaws.
“I’m pushing the aero guys as hard as I can because we need more,” Hamilton said.
“Coming from a McLaren that was so competitive… you definitely notice the difference, but it’s nowhere near as bad as it could be.”
The Britton suffered a brake failure just 15 laps into his first run, sending him into the barriers and out of the day’s running.
It wasn’t the first incident for the Mercedes team in the two days, with team-mate Nico Rosberg being forced to stop 14 laps into his first run on Tuesday due to an electrical problem.
“I think they have given us a good base,” he said on Tuesday.
“Now it’s up to us to make the most of it, find out the problems and improve it.”
The lack of running has been a blow for the Brackley team, whose expected rivals Red Bull, Ferrari and McLaren have managed 174, 142 and 118 laps respectively over the two days.
Testing will resume on Thursday and Friday, before a two week hiatus ahead of the final two tests at the Circuit de Catalunya.