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17.5.2002
Aerodynamic efficiency of DTM Astras shows significant improvement

Opel will go to the starting grid of the third DTM race in the United Kingdom this weekend. The high-speed, selective up- and downhill bends of the demanding Donington Park circuit in particular demand a car with effective aerodynamics and a well-balanced set-up.

One of the major development objectives for the 2002 DTM Astra was a notable increase in aerodynamic efficiency, calculated as a quotient of downforce and drag. The coefficient of drag which, in the production Astra Coupé reaches an excellent Cd-value of 0.28, has clearly been raised for the racing Coupé, owing, for example, to enormous wheel arch extensions, but also to air ducts for cooling water, oil, brakes and gearbox. "The impact of these air ducts on drag and downforce, resulting from such factors as the location and design of the air intakes at the front apron must be kept at an absolute minimum," said Martin Gerspacher, aerodynamic expert with Opel Performance Center (OPC).

Extensive simulations helped create a 40-percent scale model of the racing Astra used for investigating air flow and downforce behaviour in the wind tunnel of Fondmetal Technologies in Italy. Because DTM regulations only allow one particular aerodynamic configuration per racing season, these investigations were soon followed by wind tunnel tests of the original vehicle at the University of Stuttgart and, of course, on the track itself.

In pursuit of aerodynamic balance
Aerodynamic forces lead to higher wheel loads, which means that higher forces can be transmitted via the tyres. This results in higher cornering speeds, better braking deceleration and higher traction when accelerating from corners. The rear aerofoil is the most conspicuous aerodynamic component. The restrictive technical regulations of the DTM prescribe both the spoiler profiles and their position. A considerably higher developmental effort is invested in the air flow underneath the vehicle. Whilst a flat underbody is mandated between the axles, the front splitters and the diffuser provide for the so-called ground effect.

Based on a carefully crafted shape worked out in wind tunnel tests, the air underneath the front spoiler is accelerated, with the higher air flow velocity creating a suction or vacuum-like effect on the vehicle. Front flaps located on the left- and right-hand sides of the vehicle front, which may be removed for performing the balanced vehicle set-up, increase downforce. The diffuser, which sucks out the air from underneath the vehicle, thus creating a suction or vacuum-like effect at the vehicle's rear, works in a similar way as the front splitter. The wedge shape resulting from a change in the vehicle's position through front and rear ground clearances is an another major factor in this.

Individual driver needs
The differing characteristics of the DTM race tracks and the individual needs of the drivers require utmost exploitation of aerodynamic potentials. As such, the Norisring requires the least amount of downforce, whilst the Sachsenring, for example, requires a very high-level one. On the other hand, a high degree of downforce frequently leads to understeering, because the "aero-balance" has been shifted excessively towards the vehicle rear. "This often results in conflicting interests, which means that optimal balance is always a compromise," according to Michael Bartels.

Timetable

DTM, Donington Park (GB)
17-19 May 2002

Friday, 17 May
09.00-09.15 DTM Roll-out
10.30-12.00 DTM Test 1
14.30-16.00 DTM Test 2

Saturday, 18 May
09.00-10.00 DTM Free practice session
12.05-12.50 DTM Qualifying
13.45-14.15 DTM Pitwalk

Sunday, 19 May
09.30-10.00 DTM Warm-up
12.25-13.15 DTM Pitwalk
13.30-14.00 DTM Starting grid presentation
14.15 DTM Qualifying race (8 laps)
15.00 DTM Feature race (25 laps)

Times: Local British time – Germany plus one hour