Scratching the 73-Year Itch
It's Bentley's bid, seven decades later, to reclaim the Le Mans throne. It's an experimental car. We're going 190 mph.
“Whatever you do, don’t touch that,” Derek Bell hollers through his helmet, pointing to the very large red button on the dashboard that controls the Halon fire extinguisher. “It takes all the oxygen out of the air and you pass out.”
All I can do is nod dumbly. In the 1970s, Bell was one of the top racecar drivers in the world, winning Le Mans five times; and now that we’re sitting side by side in the suffocatingly hot cockpit of Bentley’s new Speed 8 sports car, I’ve pretty much put myself at his mercy. A few seconds and several micrometers of well-laid rubber later, we’re tearing down the test track at 190 miles per hour-an experience that looks, sounds, smells, and feels like being inside a prolonged explosion. The world shakes. The air reeks of gasoline. And with 3 Gs pinning me to the window through each turn, I couldn’t hit the red button even if I wanted to.
The Speed 8 is Bentley’s gamble, 73 years since their last win, to take the title at Le Mans. A grueling 24-hour ordeal, Le Mans is as much about endurance as it is about speed, and in the gentlemanly world of European auto racing, where the top events–Monte Carlo, the French Grand Prix–are all tuxedoed affairs, France’s venerable Le Mans is considered the most gentlemanly of all. To differentiate themselves from the rest of the pack, the “Bentley Boys” are banking on a radical departure from standard Le Mans design: a closed cockpit, which though it makes the car subject to additional handicapping design restrictions, reduces aerodynamic drag. It’s April 15–exactly two months before Le Mans–and Team Bentley has come to the Paul Ricard High Tech Test Track near Bandol in southern France to put their twin Speed 8 racecars (known as numbers 7 and 8) through 30 hours of nonstop, high-speed driving. They’ve invited me along for the ride.
“We’re trying to break the car,” explains Alistair Macqueen, Team Bentley’s technical operations manager. “In a single race we do all the mileage that a Formula 1 car does in a year. Speed is important, but durability is paramount.” I question that durability in the turns, which cause this finely tuned sports car to chatter like a 1985 Oldsmobile Cutlass Ciera on a cold day, but I am nevertheless impressed by its performance, especially at the end of my ride, when we brake from 190 to
70 mph in just 100 meters (a sensation akin to having your speed sucked away by a giant vacuum cleaner).
As the Speed 8 tears off again around the track, Macqueen explains that racecar design is subject to a complex matrix of rules, both physical and man-made. Each year the man-made rules change slightly, sending design teams into their laboratories to calculate seemingly minor adjustments to gain the upper hand. (This year, for example, the size of air-intake restrictors was cut by 10 percent, effectively making every car on the circuit that much less powerful.) But because the cars are subject to such intense physical forces–gravitational, aerodynamic, thermal–each tweak inevitably throws a thousand other details out of whack. When Macqueen and his engineers adjust the cars’ rear wing, for example, they unexpectedly increase the strain on the springs, which changes the ride height and further increases the downforce.
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.
by Courtesy Bentley
by Courtesy Bentley