Lewis Hamilton has said he expects the difference between the two Pirelli compounds being used for the Spanish Grand Prix will lead to an intriguing race weekend.

The McLaren driver struggled during the opening practice session of the weekend while using the harder compound tyre but was able to split Red Bull pair Sebastian Vettel and Mark Webber on soft rubber in the second session.

Lap times were noticeably quicker in FP2 and Hamilton admitted that it was going to be difficult to get the best out of the hard tyre through qualifying and the race.

"It's difficult to get an accurate read on pace: we stuck to our programme today and didn't appear to be too far off, but you never know what fuel-loads or engine levels the other teams are running," he said. "Still, we got some good data and made some positive improvements so, in all likelihood, we look as competitive today as we have in the past.

"We have taken some small steps forward - we put a new front-wing on and it naturally appeared to be a little bit better. Globally, it's not too bad. It didn't feel too good this morning on the harder tyre, which was difficult to switch on and difficult to make last, but this afternoon's running was very positive.

"There's a big difference between the two Pirelli compounds - and that will hopefully have a positive impact on the show this weekend!"

Team-mate Jenson Button was fourth fastest, despite struggling with the balance of his car over the course of the day.

"This morning was spent running through the new systems on the car; this afternoon was the time to push a bit harder and get a proper feel for things," he said. "I'm not particularly happy with the balance - I'm struggling with the rear-end, which isn't something I like - but I'm going to work to improve that overnight.

"There is more pace in the car, we've just got to unleash it and find a balance that I like. The longer run was reasonable, even if we got a slightly different result than we expected. But it's all good information and I think we can get a good balance for the race - now I need to focus on sorting out the rear-end for qualifying."