Pirelli's new ultra-soft a 'good step' reckons Red Bull's Ricciardo

The Red Bull driver used ultra-softs to set the second-fastest time of the second day of testing at Barcelona, with pacesetter Sebastian Vettel also using the compound.

The new ultra-soft, which is an additional fifth compound choice available this year, will be used mainly for street circuits and while teams did try a prototype version during last December's Abu Dhabi test this was the first time it has run in public.

"It just felt like another step on top of the super-soft and behaved like a softer compound, so that's good" said Ricciardo.

"It was consistent and you can expect just a little bit more grip from it.

"There was nothing strange, nothing to be concerned about and the ultra-soft was a good little step."

"It's not that relevant around here when the track is so cold, but it was good to get on it and understand it."

Changes have been made to Pirelli's slicks this year in an attempt to re-engineer the 'cliff' when tyre degradation means grip drops off dramatically at a certain point.

The changes have resulted in less rubber on the tyre and Force India driver Sergio Perez - who ended the day third fastest but did not use the ultra-soft - believes this has made it more difficult to drive when degradation is advanced.

"You can definitely notice, especially on the soft tyre," said Perez.

"Once you hit a certain level of degradation, then you start to really struggle.

"There is a lot less rubber available compared to last year, purely from what Pirelli has changed on the construction.

"So once you use a certain amount of rubber on the tyre, it becomes very difficult to keep it on track."