F1 teams could block Pirelli's planned construction change

The significance of any performance change at this stage is that teams have already made their compound choices for the later races, and some competitors may gain or lose out more than others from any variation in the expected behaviour of the tyres.

Pirelli gave all drivers two sets of a prototype tyre for use on Friday in Spa, saying it was designed "to even further protect the tyre from possible consequences generated by accidental multiple impacts on kerbs or other external bodies."

It has pursued this development route in part as a result of problems that occurred in Austria, and specifically Sebastian Vettel's right rear failure in the race.

After tests at its factory the Italian company intended to use the Spa track running to demonstrate that the construction change was "transparent," and had no impact on performance. If that proved to be the case, then Pirelli wanted the teams to agree to a change for the Malaysian GP, a decision that would require unanimity.

Technical boss Mario Isola explained: "If we are successful – not successful in terms of integrity, that was assessed with indoor testing – but the drivers are happy with the performance and handling of the tyre, we want to introduce the new specification from Sepang. This is the plan."

Although it was voluntary several teams took the opportunity at Spa to do some significant running on the revised tyres, which will also be made available in Monza.

However, it's understood that two teams have already expressed their reservations about the new design to the FIA.

"We just gave our feedback and said it was quite a significant change," one technical director told Motorsport.com.

"We were led to believe that it was transparent, that was the word they used, and we definitely confirmed it wasn't transparent to us. We did almost 150kms on them and proper back-to-backs with the standard soft.

"Our conclusion from both drivers was exactly the same. We found that it was a retrograde step from a performance perspective, which is what we're interested in.

"Basically it was a tyre that was closer to a medium than a soft, that's how the drivers described it, and that's what the lap times suggested as well. It wasn't a small change."

Isola has indicated that Pirelli could play the safety card if the teams do not give unanimous support: "If you want to introduce a modification during the year, you need the agreement of all the teams, otherwise we have to go to the FIA and ask for a safety issue. If everybody agrees, the introduction is let's say automatic."

However, in order to do that Pirelli would in effect have to write to the FIA stating that its current tyres are not safe.

Meanwhile the FIA is continuing to resist calls from Pirelli for long established circuit kerb designs to be changed. Intriguingly post-Austrian GP research showed that Vettel had experienced regular hard impacts on an apex kerb, a result of the driver's choice of line.

In other words the exit kerbs that have been called into question are not believed to have been the problem.