Cars from Beneath
Let’s alter our perspective. Quite rightly, cars have their wheels on the ground. We look at them from above, take pleasure in their design and in their gleaming paintwork. On the pages that follow, however, we take a look at some cars from beneath. That way, we see far more of their technology and find out about some exceptionally refined aerodynamics on the current models.
Like a race car, the new Audi R8 generates downforce – in the case of the V10, this measures 140 kilograms at top speed, 100 of which are on the rear axle. A fixed rear spoiler works together with a large diffuser on the underbody. Two so-called venturi spoilers direct the air into them at high speed, virtually doubling the effect. Longitudinal fins in the diffuser channel the airflow so that it doesn’t rush into the center.
Around the front axle are two small diffusers that send the air through the wheel arches and thus serve to cool the brakes. Each one works with two airflow bodies and venturi spoilers. Beneath the front of the car and the occupant cell, the underbody is almost entirely smooth.
01 Frontsplitter 02 Cooling air outlet 03 Diffuser front 04 Lower wishbone, front suspension 05 NACA-Düse für Anströmung Motor 06 NACA duct for airflow to the oil sump/engine compartment 07 Prop shaft for quattro drive 08 Pan for dry-sump lubrication 09 NACA duct for airflow to seven-speed S tronic/engine compartment 10 Venturi spoiler for increasing the diffuser effect 11 Diffuser fin
On the Audi 80 presented in 1972, aerodynamics were still a long way from being a topic. And it is also immediately evident why the cars of that era could be incredibly light and comparatively compact – the small amount of technology didn’t occupy much space. If the hood above the longitudinally mounted 1.3-liter four-cylinder with 55 hp were open, you would be able to see the stars to the right and left of the engine – unthinkable for the tightly packed engine bays of modern cars. The exhaust system is a single muffler with one narrow pipe and the rear axle not much more than that.
Nevertheless – the torsion-beam rear suspension with the front-wheel drive and the innovative negative steering roll radius at the front delivered excellent handling characteristics. The acronym EA 827 for the new range of engines would be with the entire Volkswagen Group for decades, and the curb weight of 835 kilograms shows that Audi was already leading the pack in lightweight design more than 40 years ago.
01 Oil sump for the 1.3-liter four-cylinder 02 Anti-roll bar 03 Four-speed transmission and differential 04 MacPherson suspension struts 05 Brake lines for the dual-circuit brake system 06 Diagonal brace at the rear axle 07 Rear-axle trailing arm 08 Rear-axle transverse tube, open on the underside, with integrated anti-roll bar 09 Fuel tank
Audi A4 AVANT
The aerodynamic underbody is a major contributor to the cd figure of 0,26 achieved by the Audi A4 Avant. The engine bay is completely encapsulated, with a large section of plastic cladding protecting the underside of the occupant cell. The sum of all the small details also adds up to a substantial effect: The rear-axle suspension arms are individually covered, mini spoilers – including ones in front of the wheels and on the fuel tank – provide targeted airflow guidance. In combination with the rear-end design, the aerodynamically optimized underbody ensures minimal lift at the rear axle.
As shown by the rear-axle differential and the drive shafts, the car pictured is a quattro. Also clearly recognizableare parts of the suspension, most of which are made from aluminum. At the rear, a sophisticated five-link design replacesthe trapezoidal geometry used in the previous model.
01 Wheel arch pre-spoiler 02 Wheel spoiler 03 Front-axle control arm and tie rod 04 Damping tub 05 Blocking catalytic converter 06 Heel-plate spoiler 07 Tunnel-brace spoiler 08 Wheel spoiler rear 09 Tank spoiler 10 Rear-axle control arms and drive shaft 11 Rear-axle differential 12 Control-arm cladding 13 Cover spare-wheel well 14 Cover SCR tank 15 Spoiler spare-wheel well
The revolution – this time from beneath. With its four driven wheels, the Audi quattro of 1980 turned the automotive world on its head. Some typical features of this now truly legendary sports car are also immediately recognizable. The prop shaft and exhaust system now share the center tunnel (there was still no catalytic converter at this point), the center and rear-axle differential locks were still cable operated in this model from the early 1980s. Also immediately recognizable is that the front and rear axles are practically identical, just turned around. The only space for the large muffler was at the back of the car.
The only sign of the powerful five-cylinder turbo engine in this veritable classic (bearing the German H plate for the last five years) is the oil sump, but it also shows the mounting position well in front of the front axle.
01 Cladding for the side-mounted water cooler 02 Oil sump for the five-cylinder turbocharged engine 03 MacPherson suspension struts, control arms, coil springs 04 Half shafts, front 05 Center differential with cable-actuated lock 06 rop shaft with articulation 07 Exhaust system, still without catalytic converter 08 Drive shafts rear 09 Rear-axle differential with cable-actuated lock 10 MacPherson struts, control arms, coil springs
Audi Rallye quattro A2
Rally tracks were, of course, the perfect stomping ground for the quattro. And in 1981, Audi proved the superiority of the permanent all-wheel drive system to the motorsport world. 1984, the build year of our 360 hp example of the A2 generation, began with Walter Röhrl’s victory at the Rally Monte Carlo and ended with Stig Blomqvist claiming the world championship title.
Aerodynamics do not feature in this underbody, which called for toughness in the face of intense contact with gravel, stones and sometimes even rocks. The MacPherson suspension front and rear is far more robust than the one on the production car, but also lighter. The second generation of the Rally quattro had a homologation weight of just 1,000 kilograms. And, of course, not only is the exhaust system completely minus any form of muffler, it also has a considerably larger diameter than on the road car. For a good 50 percent more power, it also needs a proportionately higher airflow. The battle scars from its active period more than 30 years ago are still evident on this quattro – despite having been carefully preserved for posterity.
01 Headlamp battery for night stages 02 Series-production bumper 03 Protective panel for engine/transmission unit 04 MacPherson struts with additional trailing arms 05 Center differential, partly locking 06 Exhaust pipe minus muffler 07 Prop shaft 08 MacPherson struts with additional trailing arms 09 Protective panel for rear-axle locking differential 10 Recovery hooks
Audi R15 TDI
From the Audi R8 to the R18 e-tron quattro, Audi has been dominating endurance racing and the 24 Hours of Le Mans for the past decade and a half – and aerodynamics have always been an important part of the winning package. While the closed cockpit has been the better solution since 2011, Audi’s victories from 2000 until 2010 were achieved with open prototypes. The R15 had a ten-cylinder TDI with 5.5 liters of displacement and an output of around 600 hp.
In a race car, perfect aerodynamics always mean the perfect balance between downforce and drag. The most significant “disturbance variables” are the wheels. The most important element is the underbody, which looks so simple on the photo. Nevertheless, this is where 70 percent of the total downforce is generated.
01 Areas of heavy wear and tear protected by inexpensive wooden panels 02 Front diffuser 03 Complete front end in one single piece, for speedy replacement 04 Cooling airflow to the brake system 05 Front part of the monocoque with suspension 06 Area between the wheels angled outward 07 Wooden panel exactly specified by the regulations defines the minimum vehicle height 08 Rear diffuser generates downforce, calibrated precisely in accordance with the shape of the rear end and the wing