Renault's world champion Fernando Alonso fired off a warning to his Formula One rivals on Friday by lapping comfortably quicker than them in French Grand Prix free practice.
BMW Sauber's Robert Kubica topped the timesheets in both sessions but the young Polish test driver will not race on Sunday.
Alonso, winner of six of the 10 races to date and 19 points clear of Ferrari's Michael Schumacher in the standings, was second quickest in the afternoon session after sitting out the morning.
His time of one minute 17.498 seconds was the fastest by a race driver on a day dominated by the unsung testers.
Of the 22 drivers who will be on the starting grid at Magny-Cours, only four made the top 10 in the second session -- Renault's Italian Giancarlo Fisichella the fifth quickest with a lap of 1:17.916, ahead of sixth-placed Schumacher's 1:17.938.
Toyota's Ralf Schumacher was ninth.
Briton Jenson Button had shown promise with the third best time in the opening session as most of the leading drivers saved their engines on a hot and cloudless Bastille Day at the circuit in the heart of rural France.
"We have made a step forward in the engine department and also in the aerodynamics. There's a lot of interesting stuff on the car," Button had said the day before.
"We won't win this weekend, you don't gain a second a lap through some small changes, but I think that we are going to carry on from Indianapolis and probably be a little bit more competitive."
Honda's reserve driver Anthony Davidson was second and third fastest in the two sessions but Brazilian teammate Rubens Barrichello crashed in the afternoon.
American Scott Speed also wrecked his Toro Rosso with a similar slide into the barriers while McLaren's Kimi Raikkonen parked up on the grass runoff seconds after the chequered flag.
The main talking point of a low-key opening session was the vertical aerodynamic fins on the nose of Kubica's car.
The winglets, first tested in Spain last week, have been dubbed the "Twin Towers" by some within the team as a nod to the Kuala Lumpur skyscrapers owned by Malaysian oil giant and sponsor Petronas.