Belgian Grand Prix: Nico Rosberg & Mercedes worried by tyre failure

Nico Rosberg says his Mercedes team do not fully understand the causes of the high-speed tyre failure he suffered in practice at the Belgian Grand Prix.

Pirelli blamed the failure on Friday on a cut, saying it could find no problem with the structure of any tyres.

But Rosberg said: "The problem is that we don't really understand it. There are theories, but no real evidence.

"That's a bit worrying. We're keeping a close eye on it and have taken measures to ensure it doesn't happen again."

Rosberg suffered the failure in second practice at 190mph as he approached the flat-out Blanchimont corner, on one of the fastest sections of the demanding Spa track.

The incident led several leading drivers to raise their concerns about the safety of Pirelli's tyres with Formula 1 race director Charlie Whiting, in the course of the drivers' briefing on Friday afternoon.

Multiple world champions Lewis Hamilton, Fernando Alonso and Sebastian Vettel were all involved in the discussion.

Hamilton starts Sunday's race - live on BBC One from 12:10 BST - from pole position for the 10th time in 11 races this season after a stunning time nearly half a second quicker than Rosberg.

Asked whether he had any concerns about tyre safety, Hamilton said on Saturday: "Not really. It is not something I can put much energy to. We have seen an incident yesterday. I don't think the tyres have looked perfect for everybody. I'm hoping tomorrow is a clean day for everyone and hopefully that isn't going to be an issue."

Rosberg added: "It's definitely still a worry for everybody. We'll just have to keep a close eye on the TV (in the race) and make sure it doesn't happen again.

"That doesn't sound very reassuring, does it?"

Mercedes F1 boss Toto Wolff said: "We have spent an awful lot of time together with Pirelli analysing what happened and really trying to tick all boxes in terms of safety and we couldn't find the problem.

"So I'm pretty comfortable that it comes down to something getting into the tyre, some kind of bizarre situation but not something we could understand.

"So from that point of view we took all measure in order to avoid. we had a couple of limits that were set by Pirelli in terms of the tyre working mechanically and we are well within those limits and have made a step even further today."

World champion Hamilton is 21 points ahead of Rosberg in the title race going into the grand prix and their closest rival, Ferrari's Sebastian Vettel who won the last race in Hungary, starts ninth.

All the drivers face their first race under new rules governing start procedures,, external after governing body the FIA reduced the amount of help teams can give drivers.

The clutch bite point cannot be changed once the car has left the garage ahead of the race and the drivers have to make all their settings adjustments to the clutch without any advice from the team.

Hamilton, who has lost the lead at the start in the last three races, said: "The team have prepared me as well as possible to get good starts. I am hoping we are able to maximise tomorrow. Everyone is in the same boat."

Full qualifying results

Belgian GP coverage details