The high-speed track suits the Red Bull car and there remain questions about the Brawn car's ability to be competitive in the lower ambient temperatures that are usual at Spa-Francorchamps.

BBC: I must find form, admits Button

"A twisty and slippery circuit will often put more heat through the tire than a fast and flowing layout as the tire is moving around more -- particularly when the ambient temperatures are high, " said Paul Hembery, managing director of F1's sole supplier Pirelli.

CNN: Ferrari chief 'concerned' by F1 rivals' progress