Pirelli could shelve prototype soft Formula 1 tyre for 2016

The Italian manufacturer opted to develop a new soft compound to make it more resistant to impacts with external objects, such as kerbs.

In practice at Spa and Monza over the last week drivers have been running on the unmarked prototype tyre to assess it.

But Pirelli racing manager Mario Isola has revealed the feedback from Spa was not overwhelmingly positive.

"There were two main areas - one was the pulling," said Isola.

"Considering the construction we were expecting a pulling on the left from the rear tyre, so we wanted to investigate this effect.

"It is a natural force of the tyre, and some cars felt the effect and some cars didn't.

"The other strange behaviour that was reported from Spa was a loss of grip compared to the current soft specification.

"This is really strange because although there is a change to the construction, the compound is the same. I cannot explain why they felt less grip."

Isola also revealed there was a difference in lap time, with one team claiming it was 0.8 seconds slower per lap with the prototype compared to the current soft tyre.

"Spa is a long lap with a lot of corners, so the lap time is quite high compared to other circuits," added Isola.

"We need to quantify this difference, and if it is very small then I don't see a reason why we shouldn't introduce it.

"If the difference is big then there is an effect we are not considering and we need to better understand why we have this difference in grip before introducing the tyre."

Pirelli will now assess the feedback from the teams and drivers following practice in Italy before compiling a report and sending it to the FIA.

A decision will then be taken on whether to introduce it for the Malaysian Grand Prix at the start of October.

"We need to be quite quick with this because if the prototype is OK then we want to introduce it in Sepang, but this means we have to produce, deliver and ship the tyres, so we need to conclude quickly and decide what to do," said Isola.

"We will consider all the effects, and then we will discuss with the FIA whether it is worth introducing or not.

"If we want to introduce it later it means we won't have an additional test, so probably if we don't introduce it in Malaysia then I am not sure we will introduce it for this year.

"If we want to introduce it in Malaysia it means that next week we need to have all the data available, and then we will take a decision. It needs to be done by the end of next week."