Belgian GP: Pirelli surprise at Ferrari tactic after Vettel blowout

Vettel's bid for third place at the Spa-Francorchamps circuit was wrecked on the penultimate lap when his right-rear tyre blew along the Kemmel Straight.

The four-time champion let rip at Pirelli post-race, slamming the tyre supplier's performance as "unacceptable", suggesting the consequences could have been far worse if the incident had occurred 200 metres earlier going through Eau Rouge.

Team principal Maurizio Arrivabene has suggested the one-stop plan, with Vettel switching from soft to medium compound tyres on lap 14 of 43, "was absolutely right".

Hembery has made clear wear, as opposed to the cut that accounted for Nico Rosberg's right-rear tyre in practice on Friday, was the cause on this occasion.

Although Hembery has confirmed Pirelli provided the teams with an indication tyres would last 40 laps, he insists that is not a guarantee as circumstances of a race play a part.

"It [Vettel's tyre] was at the end of wear life. Any time in the world, when it gets to the end of its wear life then you're going to have a problem," said Hembery.

"We thought the strategy was going to be based on two, three stops as you saw the majority do. They [Ferrari] felt clearly they could make it work on the one-stop.

"The wear life was indicated at around 40 laps, but it's an indication. You don't guarantee because it's variable car-to-car, on the race conditions, race situation. Sometimes it's not a precise data.

"Other teams were clearly taking a different direction, on two or three stop strategies, so that gives you an indication of where the majority were thinking."

Asked whether he was concerned Ferrari opted for a one-stop plan, he replied: "We were surprised."

Suggested to Hembery Ferrari took a gamble that did not pay off, he said: "That's probably the easy way to say it at the end of the race, but that's with hindsight.

"If the race had been one lap less he'd be on the podium and you would have said 'What a genius move'. So that's tough."

As to Vettel's post-race fury, in which he accused Pirelli of using debris or drivers' mistakes as excuses for its own failure, Hembery said: "You can always understand a driver's reaction, hot out of a car.

"I'm not going to say anything negative about that. With time you have a chat with him, but that's normal."