In December 1978, wind tunnel testing began on the Tempo, with more than 450 hours of testing resulting in more than 950 different design changes. As part of these changes, the Tempo and Topaz both featured 60° windshields, matching those of the new Thunderbird and Cougar. Also new were the aircraft-inspired door frames, which originally appeared on the Thunderbird/Cougar. These door frames wrapped up over the edge of the roof which improved sealing, allowed for hidden drip rails, and cleaned up the A-pillar area of the car significantly. The rear track was also widened, creating more aerodynamic efficiency. The front grille was laid back more and the leading edge of the hood was tuned for aerodynamic cleanliness. Wheels were pushed out to the edges of the body, decreasing areas where air turbulence would be created. The rear of the cars were treated to just as many changes. The rear window was laid down at 60 degrees as well, and the trunk lid was raised higher than the side windows. This allowed the air to flow off the car more smoothly, and allowed for greater fuel efficiency. From the side view, this raised trunk created a wedge look to the car which was especially prominent on the two-door coupe versions.