The Aero X was an experimental aerodynamic concept car built by General Motors in the United States, presented as a four-door, four-seat saloon and shown as one of the first public results of research carried out in the large wind tunnel that had recently entered service at GM's engineering and design centre in Warren, near Detroit. It was constructed as a glass fibre prototype and tested in the wind tunnel both as a reduced-scale model and at full size. The car was based on the Chevrolet Citation, GM's compact "X" car platform, which was also sold under the Pontiac Phoenix, Oldsmobile Omega and Buick Skylark names and used front-wheel drive with a transversely mounted engine.
Irvin W. Rybicki, GM vice president in charge of the Design Staff, presented the Aero X as an example of the company's ongoing aerodynamic studies, stating that efficient cars could be designed without sacrificing comfort or appearance and describing the project as a step in a product-improvement effort GM intended to pursue further. He also noted that the car used technology still under development and could not be turned into a production model immediately, while emphasising that it demonstrated what could be achieved when GM's engineering and design staff worked together.
Using the Citation's basic dimensions unchanged, the Aero X reduced its drag coefficient from 0.45 to 0.285, a reduction of about 40 percent, measured in GM's Engineering Staff Aerodynamic Laboratory. For comparison, the contemporary Vauxhall Cavalier saloon had a drag coefficient of 0.38. The roofline was lowered by around 5 cm (nearly two inches) compared with the standard X-car, while shoulder room inside remained the same, and the frontal area was reduced by six percent. Despite the sloped, streamlined nose, the front overhang was barely lengthened. The bonnet sloped in a continuous curve into the windscreen to smooth airflow over the upper body, and cooling air reached the engine through an inlet positioned beneath the nose rather than a conventional grille. The headlights were retractable.
The body design avoided applied mouldings and used flush-fitting glass all around, with the body pillars set behind the glazing to keep the surface smooth; the door pillars were made deliberately thin. Wipers were recessed into the bodywork, and the wheel covers sat flush with the wheels, which were mounted in line with the body surface. The tail of the car was also shaped to allow smooth airflow off the rear, giving it a cut-off appearance. Low-profile, wide Pirelli Cinturato P7 tyres were fitted to the wheels. Each wheel opening was fitted with a flexible cover that allowed the wheels' vertical and steering movements while reducing the aerodynamic drag normally generated inside the wheelhouses.
The underside of the car, from the front air inlet back to the front axle, was carefully shaped and largely enclosed. A pair of wedge-shaped forms widened progressively from beneath the nose, reaching maximum width at the front of each wheel opening, directing air not needed for engine cooling smoothly underneath the car. Two wedge-shaped slots in the underbody handled the extraction of cooling air after it had passed through the engine bay.
Mechanically, the Aero X carried over the Chevrolet Citation's 2471 cc four-cylinder engine, producing 85 hp at 4000 rpm and 170 Nm of torque at 2400 rpm, driving the front wheels. The car measured about 450 cm in length and 130 cm in height, with a wheelbase of 266.5 cm and a track of 149 cm at the front and 144.5 cm at the rear.
According to Rybicki, the reduced drag coefficient translated into a potential fuel economy improvement of about 4 mpg, equivalent to roughly 0.6 litres per 100 km, over the 1981 production X-car when measured on the US government's combined city and highway EPA driving cycle. He noted that achieving the same fuel saving through weight reduction alone would require removing several hundred pounds from a standard X-car, a figure given as around 600 lbs (270 kg) in some accounts, achievable only through extensive use of costly lightweight composite materials and likely requiring changes to manufacturing methods.
The Aero X remained an experimental concept rather than a production vehicle. GM presented it as a demonstration of aerodynamic possibilities rather than a car intended for the market, with Rybicki stating that the company's work in this area was ongoing and that the drag reduction achieved on the Aero X pointed toward further effort still needed in future product development.
