Friday form guide: far closer than it looks

Tyres were back in the news for the wrong reasons after second practice at Spa, with sudden deflations of the right-rears on the cars of Sebastian Vettel and Fernando Alonso.

In both cases by the time the tyre punctured they were at Stavelot, where that tyre would be the unloaded one - the assumption being that if the puncture was induced by a structural failure in the tyre, the damage would have been done in the preceding fast left-hander of Pouhon.

At the time of writing Pirelli was still trying to determine the cause, but it had pictures showing two piercing holes in the tread of Alonso's tyre and a circumferential groove of damage in that of Vettel's.

"The suspicion is that there is something on the track that was damaging the tyres," said Pirelli's Paul Hembery. "We saw several cuts on the tyres of other cars too."

In terms of pace, Red Bull set the headlines, Sebastian Vettel marginally faster than Mark Webber with a slightly lower rear wing.

Grosjean trailed the Red Bulls for single-lap pace, but may have been running heavier © XPB

Romain Grosjean's Lotus was next, over 0.8s behind. But in Hungary it became apparent on Saturday that Red Bull had been running the Friday sessions significantly lighter than most others.

If it has adopted a similar strategy here, it would explain much of that difference - because on long run pace Grosjean's times were directly comparable with those of Webber's Red Bull on the same compound of tyre.

Mercedes was only ninth and 12th quickest with Nico Rosberg and Lewis Hamilton respectively, but most of the time loss was in the long-straights of the first and third sector.

Given that both drivers could be heard making downchanges into sixth before the top of the hill after Eau Rouge, it can be assumed that the engines were being run in very conservative mode - the team has a lot of careful juggling to do with engine mileages for the remainder of the season if it is to avoid grid penalties for engine changes.

Expect them to be bang on the pace, as usual, in qualifying.

Rosberg's long run was not as quick as those of the Red Bulls and Grosjean's but, taking into account the less aggressive engine use, it looked very promising on both types of tyre. Hamilton was suffering with several braking lock ups.

Ferrari was hit by a variety of mechanical problems © XPB

Ferrari had a very inconclusive second session, with various mechanical problems on both cars that prevented Fernando Alonso having a proper long run.

Felipe Massa was less affected and put together an eight-lap run on the option tyre that averaged only a few tenths off that of Grosjean.

Jean-Eric Vergne was consistently nibbling away at the top teams in the Toro Rosso, fifth quickest in headline low fuel times and with strong, consistent long runs.

In summary Red Bull, Lotus and Mercedes all look in potentially good shape, Ferrari look quite respectable in race trim but will probably struggle, as usual, in qualifying.