Bentley EXP Speed 8

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Taking Bentley back to the Le Mans victory rostrum was a more complex task than the cynics suggested. As its designer explains, despite its Audi roots it was much more than a converted R8

For British motorsport fans, 2003 rekindled memories of 15 years earlier. Then it was Jaguar repeating past glories by winning Le Mans for the first time in decades; now it was Bentley’s turn. But there were differences: Bentley wasn’t allowed to try to repeat its triumph in following years, and some misinformed voices claimed that the EXP Speed 8 was only an Audi R8 with a roof, painted green.

The Bentley project began in the wake of the rushed Audi R8C of 1999. Initially an unbadged, Cosworth DFL-powered prototype, it might eventually have carried the name of any manufacturer in the Volkswagen-Audi Group. But VAG’s acquisition of Bentley in 1998 presented an irresistible opportunity to invoke memories of the Bentley Boys’ exploits in the late 1920s. So a Bentley it became, designed and built at Audi’s Racing Technology Norfolk subsidiary in East Anglia.

Talking about car and programme here are Peter Elleray, the EXP Speed 8’s chief designer, and Guy Smith, who campaigned the car in 2001 and 2003, and was test driver in 2002.

Coupe versus open

PE: “A surprising number of pretty well informed people think that making a coupé to those regulations was just a matter of putting a roof on an open car. But it was much more than that – it was a completely different car to the Audi, with a completely different chassis. A coupé was at least 50 per cent more difficult to make. You needed twin roll hoops that had to meet some pretty stringent strength tests, so the closed car needed a very different structure. The doors were a massive issue too. Not only did they complicate the construction, they also put a big hole through the sidepods and all the radiator ducting, which you had to try to seal up when the doors were closed.”

GS: “The good thing about a coupé, especially when you are driving at night at 200mph, is that it’s eerily quiet and peaceful – you just don’t get the same sensation of speed as you do in a open car. But there are more downsides than upsides. As we found out in 2001, when you put a hot driver into a wet racing car it steams up incredibly quickly. Another problem is driver changes. That doesn’t matter so much at Le Mans, but in a sprint race it would be more of an issue.”

Aerodynamics

PE: “I thought it was a case of overcoming the aerodynamic problems of a closed car rather than exploiting any advantages. I ran the wind tunnel model without a roof and with a single roll hoop several times. Although its drag coefficient went up its frontal area came down and the drag remained pretty much the same, so we didn’t have a benefit there. Airflow to the rear wing was potentially better with a roof but the regulations required the rear wing to be lower, and of course you have a big obstruction not far in front of it. So I don’t think we gained there either. That’s really what gave birth to the 2003 car. Its cockpit was teardrop-shaped and as narrow as we could get it, with the wing as far back as the regulations would permit.”

GS: “We couldn’t get enough front downforce on the car initially, so it had quite a lot of understeer. On the 2003 car we ran a third spring on the front which controlled the dive and allowed us to get the front ride height really low. Previously if we’d tried to run the car low to get the downforce, it would start porpoising quite badly.”

Engine

PE: “I think Audi did some mapping work to suit the 2001 engine to the different restrictor sizes, but not much else. That was an OK engine – it seemed better at the Le Mans test day than at the race itself, but the rain saved that. The initial version of the 4-litre direct injection engine that we had in 2002 had a bit less power and a lot more torque, which we found difficult to use. It was a first-generation design – and that was the year Audi was going to win its hat-trick. When the full weight of Audi’s development programme was thrown behind Bentley for 2003 it became a superb engine.”

GS: “The 4-litre wasn’t obscenely stronger in any respect than the 3.6-litre. It had more torque, but the biggest problem we had in 2001-02 was putting the torque down. The ’03 car had so much better traction that it was able to make best use of the engine. The 3.6 was incredibly difficult to drive at low rpm behind the pace car or in wet conditions – it was very hard to modulate the throttle. The 4-litre made the car smoother and, particularly in the wet, more predictable.”

Tyres

PE: “The switch to Michelins for 2003 was well worth it. We ran them on the old car at Snetterton and there was a big improvement straight away, even before we’d optimised the suspension geometry. With them fitted to the 2003 car, even at the beginning of its development, it was as fast as the Audis and quicker on some circuits. Michelin then redesigned the tyres specifically for us and the car really lit up. We quad-stinted the tyres during the night in the race, which was unheard of on the narrow rear tyre.”

GS: “The Michelins were quicker everywhere but they particularly had a lot more rear bite. You could carry speed into a corner, turn in and the car would feel planted. With the Dunlops you drove off the front axle whereas with the Michelins you would feel for the rear tyres’ grip and drive off that. Over a stint the Dunlops would be very good for an initial lap time, then gradually drop away. The Michelins would drop off maybe a few tenths but then they’d stay consistent. Over the course of the race that was a huge advantage.”

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