Qualifying stats show the job Senna must do

Although there appears to be a commercial dimension to Renault's decision to replace Nick Heidfeld with Bruno Senna, it is also based on performance. The German was outqualified 8-3 by Vitaly Petrov and although he has performed slightly better in races, as you would expect relative to an inexperienced driver, this is clearly not in line with what Renault management was expecting.

It's hard for a driver to come into a team mid-season, but the team has said they expect Senna to be on Petrov's pace by Singapore. As for this weekend, I've commissioned some stats from the leading stats man in F1, Sean Kelly, to give an indication of the task facing Bruno Senna in qualifying in Spa and Monza, in comparison with Petrov to find a realistic expectation.

Heidfeld was on average 0.490s slower than Petrov on the occasions when he was behind, so that is the target Senna is aiming for on Saturday here in Spa and in Monza.

Heidfeld's performance relative to his team mate compares badly with the Rosberg-Schumacher comparison and the Alonso-Massa comparison above, both of which are also one-sided qualifying situations (10-1 in both cases).

But it compares even worse to the performance of Petrov versus Kubica last season.

Kubica was on average 0.754s faster than Petrov, who was then a rookie, last season.

Speaking in the Spa paddock this afternoon, team boss Eric Boullier explained the decision for the first time, "Every session, every weekend, the media jump on me asking why Vitaly is faster than Nick," he said. "I was not very happy with the pure speed of Nick and his global performance as an experienced driver, that is it. His leadership didn't work in the team and when you are sometimes slower than Vitaly, in fact most of the time slower than Vitaly, it is difficult for him to push the team and to settle himself as the team leader."