After three flyaway races, the teams returned to their European bases and completed a weeklong test ahead of the Spanish GP. As the fourth race in the season, this was the first chance for the teams to make major developments to their cars, and as result nearly every team had new developments for the race weekend.
Equally, the circuit marks to the first chance to really assess the relative pace - Barcelona is a favoured test track and every team knows how to get the best from its car there. Thus the race was far tighter than we've seen all year; along with the upgrades, many teams were closer to the fight than previously.
The Circuit de Catalunya has a mix of mainly fast corners, and despite the last turn being slowed for this year's race the track makes more demands of high speed aerodynamic efficiently than any other.
This punishes the left front tyre, and the hard acceleration out of the slower sections also tests traction and rear tyre wear. The long straight ensures a powerful engine is a requisite.