Summary Sebastian Vettel posted the fastest time in the second practice at the Belgian Grand Prix.
SPA (AP) - Pirelli faces renewed fears from drivers that its tires might be shredding again after Formula One champion Sebastian Vettel and Fernando Alonso had punctures in Friday s second practice at the Belgian Grand Prix.
Vettel posted the fastest time but the three-time defending champ had to withdraw with about 20 minutes of the session remaining when his right rear tire popped and the loose rubber flapped around as he made his way back to the pits. Alonso, who finished seventh in the second practice, sustained a puncture to the same tire on his Ferrari.
Pirelli faced scathing criticism following repeated incidents of tire failure in previous races, with near-farcical scenes at the Spanish GP where they shredded like confetti, turning the race into a pit-stop procession, and at the British GP where tires blew up on several cars.
That led to the threat of a boycott from alarmed drivers before the German GP and prompted Pirelli to revert back to the 2012 construction twinned with their 2013 compounds in Budapest. The modified tires held firm at the Hungarian GP last month, but Spa is a tougher track because its long, steep corners create more pressure.
"It is a worry for the sport because we have to go out and find what it is," Pirelli s head of motorsport Paul Hembery said Friday. He later met with FIA race director Charlie Whiting to discuss the situation.
Given that both punctures happened on turn 14, Hembery thinks outside factors such as debris could have played a factor, but he also said other drivers tires had surface cuts, too.
"It looks on the Red Bull as though something has been rubbing on the surface," Hembery said. "On the Ferrari there are two quite clear holes through the top of the tread. There s not a lot we can do about that."
But that explanation did not satisfy Red Bull s Mark Webber, who was second in the afternoon practice.
"We need answers and debris is not the answer," Webber said.
Alonso was more diplomatic saying: "I don t think it s a similar problem to what we saw in Silverstone, maybe more of a random set of circumstances, but all the same, it needs careful analysis."
Vettel had earlier clocked 1 minute, 49.331 seconds, which was .059 quicker than Webber and .818 faster than Lotus driver Romain Grosjean.
"Other than (the puncture), it was a positive day," Vettel said. "This morning was tricky with a few rain drops and the track was slippery. It s a lot colder here than Hungary, but that s Spa and part of this circuit."
Alonso was fastest in the first practice but when the sun came out and dried the track in the afternoon, the Red Bulls set the early pace while he was held up by traffic.
"We had a pretty good run today but there s still some performance to find and we need to get the car a bit better balanced," Webber said. "It was good to have stable conditions this afternoon."
Moments after Vettel s puncture, Dutch driver Giedo van der Garde lost control coming out of a turn and slid across the track into the crash barriers. He climbed out unharmed but there was damage to the right of his Caterham.
Hamilton also had a difficult afternoon, finishing 12th. He asked mechanics over race radio: "Is my dashboard telling me the right time? Because the car s all over the place."
Earlier, Van der Garde and Caterham teammate Charles Pic got in each other s way at the Bus Stop chicane and went off track. When Pic returned, he drove into the path of Vettel, who broke hard to avoid contact.
In the overcast morning, Alonso gave struggling Ferrari a boost.
The two-time former champion is without a win in five races and has disappointed in qualifying all season, failing to even place on the front row. But the Spaniard clocked a best lap of 1:55.198. Vettel was sixth quickest.
They set their best times when the track was at its driest, and many drivers stayed in their garages as the rain started to fall again late in the session.
Hamilton, who won the last race in Hungary, was 15th.
