Kamui Kobayashi reckons Sauber have 'definitely' made a step forward with its latest upgrades.

The Swiss-based squad ran with its new aero package last week during the three-day test at Mugello in Italy with Kobayashi setting the joint quickest time on day two.

Despite that encouragement, however, the Japanese driver knows that they will only truly see how much difference it has made this coming weekend, when the F1 circus arrives at the Circuit de Catalunya for the Spanish Grand Prix and the start of the European season.

"At the Mugello test I definitely had the feeling our new update to the car is a step forward for us. This is good, of course, but only at the Barcelona circuit will we be able to tell how much of an improvement it really is. Not only because testing never allows for proper comparisons to the competition, but also because the Circuit de Catalunya is special," he explained.

"It has everything - fast corners, medium speed corners and slow corners. Although everybody knows that track so well, it is very difficult to get the set up right there. But, in turn, if you really manage to get it right there this normally means the car can be fast on other circuits as well.

"It will be a challenging weekend for us drivers as well as for the car and the engineers, and I am very much looking forward to going racing again."

Giampaolo Dall'Ara, Sauber's head of track engineering, meanwhile echoed those views: "The Barcelona track is very complete. It has all kinds of features - low speed, medium speed and high speed corners as well as changes of direction. In some places the circuit is quite bumpy, and the tarmac is abrasive. Although we know this track well from testing it's always a challenging one," he continued.

"We tested a major upgrade to the car in Mugello, consisting of a new front wing and new bodywork, including a different exhaust exit and a new diffuser. The results of the test were encouraging.

"However, all the teams had some upgrades, and only the next race weekend will give us confirmation whether we are able to strengthen our position compared to our competitors. Nevertheless I'm confident that we can have a strong performance in Barcelona."