Sebastian Vettel edged German rival Nico Rosberg for the fastest lap in practice for the German Grand Prix on Friday, while the Formula One chief played down the drivers' threat of a pullout over tire safety concerns.
F1 boss Bernie Ecclestone said a boycott would help nobody and drivers who refused to race on Sunday risked losing their licenses.
Three-time champion Vettel is seeking his first win on home soil and beat Rosberg by .235 seconds in the second practice, after finishing eighth in the slower morning session.
Vettel's fastest lap was 1 minute, 30.416 seconds. Mark Webber in the second Red Bull was third and Romain Grosjean was fourth, ahead of Lotus teammate Kimi Raikkonen.
Next came Ferrari's Fernando Alonso, who failed to complete a full lap in the morning because of electrical problems.
Lewis Hamilton, who topped the morning session ahead of Mercedes teammate Rosberg, was eighth in the afternoon.
Ecclestone, who came to Germany despite facing possible bribery charges in a Munich case, said the drivers were right in stating that it was their neck on the line.
But he told the German newspaper Die Welt the drivers understood that Pirelli would do everything to resolve the tire issue, which turned serious when five cars endured blowouts at the British GP last week.
"There is a big difference between thinking about something and carrying it out. If the drivers boycott the race, they risk losing their super licenses," Eccelstone said. "Such a boycott would serve no one and won't solve the problem faster."
There were no punctures in the practices, although some drivers complained about the quick degradation of soft tires.
Drivers threatened through the Grand Prix Drivers' Association to withdraw from Sunday's race if tire problems persist, while Pirelli has asked teams to stick to operating requirements.
Pirelli wants all teams to remain within the prescribed pressure limits and to stop switching tires from left to right and vice versa.
The International Automobile Federation said on Friday it was the responsibility of each team to comply with the requirements.
This weekend, the belt on the rear tires is made of Kevlar instead of steel in an effort to reduce the chance of punctures.
From the Hungarian GP at the end of this month, the tires will change again, using the 2012 construction with 2013 compounds.
In the paddock at the Nuerburgring, some drivers praised Pirelli for acting quickly to rectify the problem. But the GPDA, chaired by Pedro de la Rosa and with Vettel and Jenson Button as directors, met later and decided to take their own action in order to avoid a repeat of the scenes from Silverstone.
Not all divers are members of the GPDA -- Raikkonnen and Adrian Sutil of Force India are among non-members.
