Pirelli surprised Formula 1 teams are testing ultra-softs early

The ultra-soft has been introduced as part of Pirelli's commitment to help spice up the show, with the latest rubber to be introduced at venues such as Monaco, Canada and Singapore.

On Tuesday, Ferrari's Sebastian Vettel and Daniel Ricciardo from Red Bull both enjoyed a short run on the tyre, followed on Thursday by their team-mates Kimi Raikkonen and Daniil Kvyat.

Asked whether he was surprised to see it on track so soon given teams often go for reliability over performance in the first week of testing, Pirelli racing manager Mario Isola said: "At the beginning, yes, honestly, yes.

"But then I also thought because of the nomination for Montreal they wanted some information in advance and to make some analysis with the data they are collecting.

"Considering we've had good weather, it has been the right time to test the ultra-soft.

"They were trying to understand the performance rather than the degradation. I expect big degradation on a circuit like Barcelona where we usually nominate the hard and the medium. It is not the right place.

"They ran for five or six laps and the tyres were still in a good shape, but the degradation was coming."

Under new regulations for this season teams have to nominate their choices of compound 14 weeks in advance for a fly-away event, with a decision for the Canadian Grand Prix due next Thursday.

Overall, Isola was happy with the performance of the ultra-soft, and data collected.

"Here we have the final version, and it seems it's working," he said.

"The feedback has been good, although this is not the best track on which to test it, but at least we have an indication."

As to potential improvement in laptime compared to the next tyre in the range, the super-soft, Isola said: "If you look at Ferrari the result was 0.8s per lap, but the feeling is that is a bit overestimated.

"In Abu Dhabi [when it was tested last year] we found a bit less. In my opinion the right window should be between 0.5-0.8s. That is more or less the target we had in mind."

Another new feature of this year's tyres is the under-tread layer designed to give a warning to the driver, via a feeling of a loss of grip, when he is reaching maximum wear.

To date the feedback has been positive from the drivers.

"It's not a cliff, it's quite gradual, a curve that is much more smooth, which is much better than having a complete and sudden loss of grip," said Isola.

"We will investigate better with some analysis over the next few days, but at the moment the signal appears to be good."