Nico Rosberg suffered tyre trouble in P2 in Belgium, resulting in this rather 'lucky' high-speed crash Nico Rosberg suffered tyre trouble in P2 in Belgium, resulting in this rather 'lucky' high-speed crash

The extra kerbing around Turn Four of the Spa circuit has been removed following Nico Rosberg's tyre blowout in Friday practice for the Belgian GP.

Drivers have been warned that they will be reported to the stewards if they breach the track limits at Turn Four and are suspected of gaining an advantage.

Although the change has not been directly attributed by the FIA, the sport's governing body, to the Rosberg incident, it comes in the wake of Pirelli attributing Friday's tyre failure on the German's Mercedes to an "external source" - likely to translate as kerbing or a stray piece of debris.

After an investigation, F1's tyre suppliers concluded that there were no signs of structural integrity issues with any of the tyres used and that video footage of the incident showed a problem consistent with an external cut.

"We have conducted a thorough investigation to find out exactly what happened with Nico's tyre," Pirelli motorsport director Paul Hembery said. "This investigation now excludes any structural integrity issues. Based on the information and data available an external source of damage is the conclusion made."

Rosberg's Mercedes careered off track with 20 minutes of the session remaining after his right-rear tyre deflated. Detailed analysis of the German's lap prior to his crash indicated that a blister had formed on the tyre before it exploded.

Onboard cameras showed that the 'thread' from the inside of the tyre had started to unravel on the outside on the Kemmel Straight, progressively worsening as Rosberg headed towards Blanchimont.

Rosberg was unharmed in the incident but said he was fortunate to have avoided injury.

"It was a shock," the Mercedes driver told Sky Sports F1. "Suddenly at 190mph to lose control was not good. It wasn't down to my skill, it was just luck that I stayed out of the wall."

Nico Rosberg admits it wasn't his skill that prevented a more serious outcome to his crash in P2, but luck Nico Rosberg admits it wasn't his skill that prevented a more serious outcome to his crash in P2, but luck

Rosberg ended the day top of the timesheets, three tenths clear of Mercedes team-mate Lewis Hamilton, but admitted the incident was "a bit of a dent in the confidence".

"I've never seen anything like that before," said Mercedes technical director Paddy Lowe told Sky Sports F1. "This is a tough circuit on tyres but let's not pre-judge anything."

According to Lowe, the tyre pressures and camber settings on Rosberg's Mercedes were within the parameters set out by of Pirelli.

Meanwhile, the bump behind the kerbing on the exit of the first corner has also been flattened out.