Lewis Hamilton top in Spain as Raikkonen breaks down

Lewis Hamilton headed Red Bull's Daniel Ricciardo and Max Verstappen in a difficult-to-read second practice at the Spanish Grand Prix.

Hamilton and Ricciardo were just two of a number of drivers who set their fastest times on the soft tyre rather than the theoretically faster super-soft.

Verstappen and Ferrari's Sebastian Vettel did improve on the super-soft but were only third and fourth quickest.

It meant a clear competitive picture was even harder to discern than usual.

Many drivers were struggling to make the super-soft work at all on one qualifying lap and it looked as if teams would be trying to minimise running on what was expected to be the qualifying tyre.

The unexpected situation with tyres meant that the headline lap times were potentially not a reflection of real pace.

Hamilton was 0.133secs quicker than Ricciardo, with Verstappen, using the super-soft, 0.141secs behind his team-mate.

Vettel, on the super-soft, was 0.326secs slower than Hamilton and Bottas was just 0.026secs off the fastest Ferrari.

Ricciardo's time was particularly impressive after he crashed midway through the first session and lost track time.

It indicates a potentially closely matched fight for victory, while Mercedes and Ferrari would be expected to have an advantage in qualifying thanks to their extra engine boost, which is not available to Renault.

Meanwhile, there were apparent engine concerns for Ferrari, with Kimi Raikkonen, sixth quickest, returning slowly to the pits after a puff of smoke from the rear of his car.

As with the morning session, there were a number of spins and off-track moments as strong winds disrupted the cars' aerodynamics on this exposed hillside track in the Valles region north of Barcelona.

Only one driver went off and was unable to rejoin, Haas' Romain Grosjean, but once his car was returned to the pits he went seventh fastest, making him best of the rest ahead of team-mate Kevin Magnussen.

That position may have been taken by Fernando Alonso's McLaren, but he set his fastest time on the medium tyre, did not set a lap time on the super-soft, and did not do a qualifying run on the soft.

His team-mate Stoffel Vandoorne was ninth.

Force India's Sergio Perez was 10th ahead of team-mate Esteban Ocon and Renault appeared to be struggling with Nico Hulkenberg and Carlos Sainz 13th and 17th.

Their travails were nothing compared to those of Williams, though, for whom Lance Stroll and Sergey Sirotkin were 19th and 20th, three seconds off the pace, the track brutally exposing the car's aerodynamic weaknesses.

Hamilton: "The day was pretty good, but it was a tricky one because it was so windy out there. Every driver was struggling with the changing direction of the wind.

"You're constantly arriving at each corner and the wind direction is never the same, so we saw lots of drivers going off. These conditions make it very difficult to define where the set-up needs to go.

"We've got some work to do overnight. I'm hoping that it's cooler and calmer tomorrow. I think it is going to be relatively close between the top three teams but I can't really say who is quickest at the moment."

Vettel: "It has been a tricky day with the tyres. It is very close. Could be P1 or P6 (in qualifying), but that makes it exciting."