[patrickt]

The wings were also movable. The Chaparrals used an automatic transmission, so there was no clutch pedal, which allowed Hall to add a third pedal. While accelerating, the driver would hold the pedal down with his left foot. This kept the wings horizontal for less drag. Releasing the pedal put the wings in an angled position, for greater downforce in the corners (the increased drag also helping slow the car).

Source: http://www.vintagerpm.com/can-am-history-of-chaparral/