Macqueen's main concern is aerodynamics. Partly to make a splash and partly because Bentley's owner, Volkswagen, already owns Audi, winner of the last three Le Mans, the Bentley Boys are making a go of it with closed cockpits—the only ones in the field. Doing so puts the Speed 8 in the Le Mans GT Prototype class, which means it must race with 14-inch tires instead of the standard 16-inch variety. ("Less rubber on the road means less speed in the turns," explains Bell.) To balance this handicap, Bentley is allowed to increase the size of the Speed 8's air-intake restrictors by 1mm, boosting the car's power. Of even greater benefit, though, is the reduction in drag afforded by the closed cockpit, which Bentley hopes will give the Speed 8 a leg up on open-cockpit designs, like last year's winning Audi R8.
Occasionally, though, smooth aerodynamics can work against a car, especially in the wake of recent rule changes that outlaw underbody channels and other design gimmicks that glue cars to the track with downforce. In 1999, for example, a particularly airy closed-cockpit Mercedes flew off the track and somersaulted five times before landing in a tree. "We want to reduce drag without
correspondingly increasing lift," explains Macqueen. "That's the Holy Grail."
To achieve this balance, Macqueen and his team at Racing Technology Norfolk, the firm contracted by Bentley to design the Speed 8, have made a number of key alterations to the car since the 2002 Le Mans, where it placed fourth. They've stabilized the rear wing, moved the air intakes from the roof to the sides, and resculpted the curvature of the cockpit to create a low-pressure center—a major source of downforce—under the rear overhang. Taken at a single point, this pressure is minimal (0.3 psi). But spread across the entire back third of the underbody it can reach up to a ton and a half. It's this force that, halfway through the test at Paul Ricard, causes steel brackets under the back of Car 7 to deform and snap. (Although hair-raising for those of us watching from the pit, it's an easy fix: A
few replacement brackets and the car is on its way.)
To gauge the efficacy of the Speed 8's design, Bentley placed 140 sensors in each of its cars to monitor everything from engine temperature to stress loading. This data is displayed on a bank of 20 computer monitors in an observation booth above the pit, where technicians and telemetry specialists drain a well-stocked espresso machine as they unearth potential hazards and debate design changes. Except for the brackets, they find nothing wrong. The Speed 8s are ready for Le Mans.
Cut to June 15. As the Speed 8s enter their fifth hour of Le Mans, the team notices a rise in Car 7's water pressure.
Plotted over 20 hours, it indicates a potential disaster the following morning. "We decided to bleed the line rather than risk it," says Macqueen.
That prudence pays off. Bentley's twin Speed 8s place first and second, with Car 7 winning in 377 laps (two more than last year's Audi). "We set a new distance record because we optimized our aerodynamics," says Macqueen. "But next year, there will be entirely new rules." The most significant one will reintroduce underbody channels, allowing cars to go faster without fear of flying off the track. Once again, the scales will level between open- and closed-cockpit cars—at least until the Bentley Boys figure out how to tip them in their favor.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.