Pirelli resist Red Bull pressure to make tyres more durable
Tyre supplier Pirelli has resisted pressure from world champions Red Bull to make its tyres more durable for the rest of the season.
The company has instead made one small tweak to its range following the first four races by making the 'hard' tyre slightly harder and lowering its operating temperature.
It is an attempt to prevent the excessive 'graining', seen in the Australia, Malaysia and China races, where a tyre overheats and tears.
Other types of tyre - 'super-soft', 'soft' and 'medium' - remain unchanged.
Red Bull have been pressuring Pirelli because they feel the performance of their car is being held back by the need to drive it below its optimum performance in order to look after the tyres.
Although Sebastian Vettel has won two of the first four races to lead the championship, team boss Christian Horner said after Sunday's Bahrain Grand Prix that he would still like Pirelli to re-think the tyres.
"I think the tyres are too on the edge. Needing to four-stop is a bit extreme," Horner said, referring to the number of pit stops needed by McLaren's Jenson Button and Mercedes driver Nico Rosberg.
Eight of the 11 teams asked Pirelli not to change the tyres for the remainder of the season.
The new 'hard' tyre is effectively the same as an experimental tyre that teams tried in first practice at the season-ending Brazilian Grand Prix.
That tyre was slightly softer than the 2012 'hard'. Pirelli took that information and made the 2013 'hard' tyre softer again but have now gone back on that decision.
Its lower operating temperature range should ensure it is easier for drivers and teams to make it work at its optimum. None of the remaining races are likely to have ambient and track temperatures as high as those seen in Malaysia and Bahrain.
Pirelli motorsport director Paul Hembery said: "After evaluating tyre performance over the balance of the first four races, we took the decision - in consultation with all of the teams - to change the hard compound from Spain onwards, as we did in Barcelona two years ago when we also introduced a new hard tyre for the rest of the season.
"This latest version of the hard compound is much closer to the 2012 tyre, with the aim of giving the teams more opportunity to run a wider range of strategies in combination with the other compounds, which remain unchanged."
Pirelli have also named the tyres that will be used in the next three races.
In Spain, the hard and medium will be used; in Monaco the soft and super-soft; and in Canada the medium and the super-soft.
Pirelli is looking into the cause of the tyre failures suffered in Bahrain by Mercedes driver Lewis Hamilton in final practice and Ferrari's Felipe Massa twice in the race.
The investigations are ongoing but a spokeswoman said the company was "not overly concerned".