Red Bull boss Christian Horner says he expects the F1 title fight to constantly change when the European leg of the season gets underway in Spain.

Sebastian Vettel became the first double winner of the year in Bahrain at the weekend to give him a ten point championship lead while Red Bull also tops the constructors' championship following the opening four rounds of the campaign.

The likes of Mercedes, Ferrari and Lotus have looked strong so far this year however, with McLaren also hoping to get its campaign back on track when the Spanish Grand Prix comes around.

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With that in mind, Horner said he didn't expect an easy ride through the remainder of the season and said he felt things would change from race to race as the title battle is fought out.

"The Ferrari is strong," he was quoted by Sky Sports. "Lotus have got a good car. The Mercedes certainly over a single lap is very strong. The rest are a bit of a step behind. So it's close, it's tight and I'm sure it's going to move around again from circuit to circuit in Europe.

"But to be heading back to Europe having won two of the first four races, plus a second place, it has been a strong start to the campaign for us."

While some struggled with their tyres in Bahrain compared to Red Bull, Horner also moved to deny that the defending champions have managed to come to terms with the performance of the latest Pirelli rubber.

"I think these tyres are very complex," he said. "We got it just right today: the strategy worked and the strategy in qualifying worked in conserving those tyres for the race, and Sebastian had plenty in hand.

"When you're in the window, with the balance with these tyres then you can have a dominant display like we had today. But that window is very, very fine and if you're outside of it then you can be four or five stopping."