Pirelli says that the tyre that failed on Nico Rosberg’s car in Bahrain today was a prototype – and won’t be used again.
Rosberg reported on Twitter that he’d spun on the straight after the failure. Although he quickly deleted the Tweet, his incident soon became big news.
A Pirelli statement said: “The tyre tests in Barhain regarded a number of prototypes, which were completely innovative in terms of structure and compounds, with the aim of developing the most suitable solutions for the next season.
“This morning Nico Rosberg’s Mercedes was fitted with one of these prototypes, a tyre which had only been tested in the laboratory and which will not be proposed again.
“Thus, the safety of the tyres which will be supplied for the next Championship is not in question. The accident which happened to Rosberg’s car is being investigated and the findings will be communicated to the FIA and the teams.”
Adam Cooper's F1 Blog 
Why can MotoGP manuacturers be ready with next year’s machinery the day after the last event of the season, whereas F1(TM) have to test 2014 tyres with completely different 2013 cars?