Circuit of the Belgian Grand Prix

At 4.3 miles, the Spa-Francorchamps circuit is the longest of the season and the second-fastest, behind Monza in Italy. To add to the mix, rarely a race weekend passes without rain; and it is common for that to fall on one part of the track while another part remains dry.

“It’s what I call a ‘nature’ track — through the forests — and really follows the lines and contours of the hills,” said Adrian Sutil, a driver at the Force India team, which took the pole position at the circuit in 2009 with the help of the powerful Mercedes engine. “For me, it is the best circuit on the calendar as it has some of the most spectacular corners of the year.”

The one everyone talks about is called Eau Rouge, which from certain standpoints looks like a wall through the forest to the sky. It is at the end of a back straight where the cars run at 300 kilometers an hour, during a 23-second period at full throttle from La Source hairpin to Les Combes, at the end of the straight after Eau Rouge. Eau Rouge is the only corner in the series where the drivers have negative G-forces, here measured at up to -3.5g.

Spa is also a challenge to engineers.

“Sectors 1 and 3 require low drag, while Sector 2 requires maximum downforce, so a well-compromised set-up is crucial for getting a quick lap time,” said Sam Michael, the technical director of the Williams team.

It is the second most demanding track on the engine — Monza being the first — and it therefore tests engine durability, and also the car’s tires.

“The change from downhill to uphill through Eau Rouge puts the tires under severe compression forces at high speed added to the downforce and inertia loads, so tire pressures need to be carefully determined and monitored,” said Hirohide Hamashima, the director of tire development at Bridgestone.

Michael Schumacher holds a record six victories here, Ayrton Senna won it five times, and both Jim Clark and Kimi Raikkonen have won it four times.

“It is a real test for the drivers,” said Colin Kolles, the director of the HRT team. “The wheat is separated from the chaff.”