Nuerburgring, Germany: There was no sign of the tyre blowouts which marred last weekend's British Grand Prix in first practice in Germany on Friday as Lewis Hamilton topped the timesheets in his Mercedes.
However, Ferrari's Fernando Alonso had an electrical problem with his car and failed to set a time.
Under gloomy skies, which mirrored the mood of Spaniard Alonso after he ground to a halt just off the track in his first practice lap, Hamilton's Mercedes team-mate Nico Rosberg set the second fastest time.
Ferrari said on Twitter that it was an electrical problem and the championship contender only managed one more lap before being recalled to the pits for further checks.
Hamilton edged out Sunday's Silverstone winner Rosberg on his home track with a time of one minute 31.754 compared to 1:31.973 but the Briton's engineer reported DRS problems over the radio.
The Grand Prix Drivers' Association announced on Thursday that they will withdraw from Sunday's race if the five tyre blow-outs from Silverstone occur again but practice was free of incident.
After the intervention of the governing FIA, Pirelli has brought upgraded rear tyres to the Nuerburgring with an inner belt made of the synthetic fibre Kevlar rather than steel.
The tyres are not totally new to the teams as Pirelli offered them for practice in Canada last month but bad weather meant teams used them sparingly in Montreal and did not gather much data.
Red Bull's triple world champion and championship leader Sebastian Vettel was only eighth fastest in first practice with another session coming later on Friday and a third before qualifying on Saturday.
Vettel, who has never won in Germany, is 21 points ahead of Alonso after eight races.
Mark Webber, preparing for his final German Grand Prix as he quits for endurance racing at the end of the season, was third quickest at the circuit where he took his first Formula One victory in 2009.
Marussia's Venezuelan test driver Rodolfo Gonzalez was allowed to drive Jules Bianchi's car for first practice and clocked 1:37.459 as the slowest out on track.