Eau Rouge: the toughest turn in motorsport
Ahead of the Spa 24 Hours, works driver Laurens Vanthoor and Sebastian Golz, Project Manager Porsche 911 GT3 R, relive Eau Rouge at full throttle
Exiting the La Source hairpin, Laurens Vanthoor stamps on the gas. The 500+hp 911 GT3 R catapults out of the first corner at Spa-Francorchamps, accelerating rapidly downhill. After a fast righthand kink, the Belgian hugs the wall that separates the old pit lane from the circuit. In the distance is Eau Rouge. Flat out or lift? “That’s always a tricky question until you dare to do it for the first time,” he laughs.
During the 24 Hours of Spa-Francorchamps this weekend, drivers will face this dilemma every single lap. The corner combination, which is officially known as ‘Raidillon’, owes its now famous name to a nearby creek where the high iron content of the water tinges it red – hence Eau Rouge.
On fresh tyres and a dry track with minimal fuel, qualifying is often flat out through Europe’s most fearsome corner. But it’s a different matter in the race. Over 24 hours, cars will cover more than 2500km, passing through Eau Rouge hundreds of times with differing fuel loads and degrees of tyre wear. The section produces a huge compression combined with massively high cornering speed.
After the downhill comes a left-hander at the lowest point followed, by a sweeping, fast righthand corner leading to a steep climb and the final left-hand kink. Visibility is so limited that for a short period of time drivers see only sky and treetops. “When you negotiate this passage for the first time,” says Vanthoor “it’s a truly nail-biting experience.”
“At around 240 km/h, not only the drivers but many components come under extreme stresses,” adds Golz. “Through the dip at Eau Rouge, the tyres get extremely compressed, and at the same time lateral forces of up to 3.0g deform the sidewalls. With the GT3 R, this means that around five tonnes is pushed to the outside of the corner. In the compression, the vehicle briefly bottoms out at up to 2.5g. The tyres alone can’t absorb these forces. The rims distort and even the chassis seems to groan.”
The 911 GT3 R is designed to distribute forces evenly across the chassis without overloading certain areas and every component plays a part in reducing the amount of energy that impacts the vehicle. But when preparing for Eau Rouge, setup plays a vital role.
“For rapid changes of direction, the car should have quite a hard setup, but this would never work through Eau Rouge,” explains Golz. “Through the compression, high forces cause massive load changes. A hard setup might result in having one wheel in the air without surface contact. This should never happen there. You need all wheels on the ground for maximum grip.”
Conversely, if the car’s suspension is too soft, it will bottom out badly in Eau Rouge. So a compromise has to be sought. “It’s not the shocks reaching their limit – we can do something about that,” says Golz. “It would be much more serious if the entire chassis bottomed out. This would minimise the wheel load and reduce the grip significantly. We’ve got to find a good compromise to ensure maximum contact of all wheels on the ground at all times.”
Eau Rouge is always a factor in the set-up for Spa, but the rest of the 7 km circuit has to be taken into account. For fast corners like Pouhon or Blanchimont, a low ride height is essential for high downforce, while passages with rapid directional changes like Les Combes or the Bus Stop chicane require firm suspension, both at odds with the demands of Eau Rouge.
As a driver, mastering this section takes skill, confidence, a wealth of experience and a huge amount of courage. “It may sound strange, but Eau Rouge is easier to take at full throttle than lifting for half a second,” says Vanthoor. “At this spot, the driver has to be absolutely sure about what his car is doing. If I lift approaching the lowest point, the load shifts to the front – and the car pitches. This affects the steering behaviour and I might hit the kerb too hard. If this happens, things get seriously tricky. As a driver, you’ve got to learn Eau Rouge by driving it. Everyone knows that aerodynamics offer more downforce at a higher speed. Obviously you shouldn’t try to overdo it, but with the GT3 R, you can keep the pedal to the metal – most of the time. It doesn’t always work – sometimes your gut tells you that it would be a good idea to lift for a split second.”
This is something than Golz can’t help but agree with. “On one hand, we technicians like to see the drivers going full throttle through Eau Rouge,” he says. “After all, we’re passionate about motor racing. But it’s obvious that neither the tyres nor the vehicle would withstand these stresses over long periods of time. So we’re quite happy that the enormous physical and mental stresses through this passage keep the drivers from trying to tackle it at full tilt most of the time.”