GP2 returns to action this weekend after sharing F1's August "summer holiday", with the series' teams and drivers looking forward to one of the most famous, historic, beautiful and fiendishly challenging circuits of the year - Belgium's Spa-Francorchamps.

Going into Spa, the only driver change announced for the weekend is at Ocean Racing Technology, which has decided to replace Kevin Mirocha with 21-year-old New Zealander Brendon Hartley.

The Formula Renault 3.5 regular - who has two front row starts in the series, finished on the podium at Monaco earlier this year and is currently seventh in the championship - previously raced for Scuderia Coloni in the final two GP2 races of 2010 at Monza and Abu Dhabi and finished in the points in the last race of the year. A former Red Bull Racing/Toro Rosso third driver, Hartley then tested with Ocean over the winter.

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"Brendon already knows our team because he drove with us last winter: he is an experienced driver, he's fast, and he is very mature thanks to his experience in F1," said team principals Jose Guedes and former F1 driver Tiago Monteiro in a press statement. "We had other alternatives but we have been following Brendon's career very closely and we wanted to give him this opportunity."

"I am very enthusiastic and happy about the chance I have been given," said Hartley. "I know the Spa track well and my objective is to be competitive there."

Hartley will be at the wheel of the #22 Ocean car, alongside his team mate for the weekend Johnny Cecotto Jr., who himself is looking forward to the challenge of Spa: "It is an extraordinary circuit that I always adapt well to," said the Venezuelan. "I especially love its fast corners ... I really think that the conditions have come together so that we can fight for a spot on the podium."

Coloni itself has already confirmed that they will be sticking with Luca Filippi once again this weekend as they approach Spa with reason for optimism - last year, their car put Alvaro Parente into second place in the feature race and third in the sprint.

"Luca loves Spa and he already got on the podium there [in 2007 with ART]," commented team boss Paolo Coloni, who said that he was confident that the team was "charged-up and confident that our luck has changed," after admitting that the first part of the year had been a struggle after they lost their primary driver Davide Rigon to injury at the end of the sprint race in the season open in Turkey.

"Rigon's injury forced us to change our plans but working hard together we managed to overcome all the odds and clinch some great results," said Coloni. "I'm very proud of how the team reacted to all the bad luck we had," he added, clearly looking forward to putting that all behind them with hopes of success at one of the most beloved but demanding circuits on the calendar.

According to Pirelli Racing manager Mario Isola, Spa "is one of the most challenging race circuits in the world thanks to its fast, undulating and twisty nature which probably demonstrates the importance of driver skill more than on any other circuit in the world."

Its unique blend of characteristics has led to Pirelli opting to supply teams with the medium compound P Zero GP2 slick tyres for the weekend, which Isola describes as "versatile tyres designed to work well in a wide range of conditions.

"They can be used at hot and technical tracks as well as at much cooler or even damp circuits, making them a perfect choice for Belgium because of the weather, which is quite unpredictable," he added.

And Spa is certainly notorious for its changeable weather, with rain capable of appearing without warning out of nowhere in the mini-climate of the Ardennes forest near Liege. The size of the sweeping 7.004km circuit adds to the difficulties of reacting to the weather, as one side of the track can be awash with rain while another part is bone dry.

"Adding to the challenge of the weather will be the extremely high vertical loads which put heavy demands on the rubber," continued Isola, pointing out the particular part of the track through Eau Rouge and Raidillon which he describes as presenting "probably the heaviest [loads] of the racing calendar."

Neither of last year's race winners will be in the field for the start of the Spa weekend: Pastor Maldonado (who won the feature race) is now with Williams F1, while Sergio Perez (who won the sprint event) will be lining up on the Grand Prix grid for Sauber.

Instead the field is headed by GP2 Series leader Romain Grosjean, who comes into Spa with a 25pt margin over his nearest challenger Giedo van der Garde and could clinch the 2011 title this weekend. Given the ructions going on at the Renault F1 team where Nick Heidfeld has just been ejected and replaced by Bruno Senna for Spa and Monza, Grosjean will have half an eye on a return to F1 if he can just clinch the GP2 championship in style.

The weekend's activity starts with practice on Friday morning at 10.55am BST following the F1 Free Practice 1 session, then qualifying in the afternoon at 2.55pm BST.

The feature race consisting of 25 laps starts at 2.40pm on Saturday afternoon following the F1 qualifying, with the sprint race of 18 laps on Sunday morning at 9.30am. Both races are scheduled to be broadcast live on British Eurosport in the UK.