Sebastian Vettel was among the drivers to voice his displeasure with Pirelli's tyre choices after Friday practice for the Spanish Grand Prix.

Pirelli has brought hard, medium and soft tyres -- the three compounds at the hardest end of its scale -- to the Circuit de Catalunya, a decision criticised by most drivers ahead of the weekend. That selection was made before pre-season testing and is the last to adhere to a set allocation of compounds decided by Pirelli before the teams are once again free to pick the quantities of the three compounds from Monaco onwards.

Grip was an issue throughout the 180 minutes of running on Friday as many drivers running wide and struggling to 'switch-on' the tyres. Vettel has suggested Pirelli has been too conservative with its choices because of the high loads placed on cars at the circuit.

When asked if the race would be a straightforward one-stopper or if there was a chance for variety on strategy despite, Vettel said: "I don't know. I think today was quite a shocker if you look at the long runs, I just had a very short glimpse and everyone was struggling due to the conditions. I was on the medium, it was quite slippery, very interesting.

Mirko Stange/Sutton Images

"I think a lot people suffered degradation on the soft, but generally tyres feel a bit hard. I don't know why, I think it is the myth of Barcelona Pirelli is afraid of but by Sunday things calm down, the track picks up and we should be alright. But there could be some windows for strategy."

Renault's Jolyon Palmer thinks the tyre choice meant much of Friday's track time was irrelevant for the teams.

"We are kinda getting half of the running that we normally would because everything we do on the hard tyres was irrelevant and the medium are difficult and the softs is what counts for qualifying," he said. "[The mediums] are very hard and they are a very low-grip tyre. We need to use them in the race of course, but for low-fuel stuff, they are so far off the soft that you do not really learn anything."