Paul Vance and his wife, Cynthia, invited Carl and Jeanne Leichtamer, (Ps) brother and sister, to go for a ride in the Vance's Jeep Model CJ-7. They drove to the Hall of Fame Four-Wheel Club. The Vances were seated in the front of the vehicle, and the Leichtamers rode in the back. The club was an 'off-the-road' recreation facility with a course of hills and trails about an abandoned strip mine. As Vance drove over the brow of a hill, the rear of the vehicle raised up relative to the front and passed through the air in an arc of approximately 180 degrees. The vehicle landed upside down with its front pointing back up the hill. The pitch-over killed the driver, Paul Vance, and his wife, Cynthia. Carl Leichtamer sustained a depressed skull fracture. Ps, who are the only surviving eyewitnesses to the accident, described the vehicle as traveling at a slow speed. Ps sued American (D). Jeanne Leichtamer is a paraplegic as a result of the injury. D's expert testified that the vehicle had to be traveling between 15 and 20 miles per hour. This conclusion was based on evidence that the vehicle landed approximately 10 feet from the bottom of the second slope, having traversed about 47 feet in the air and having fallen approximately 23.5 feet. Vance purchased his Jeep CJ-7 from a duly-licensed, factory-authorized dealer. The vehicle came with a factory-installed roll bar. The entire vehicle was designed and manufactured by Jeep. Ps did not claim that there was any defect in the way the vehicle was manufactured in the sense of departure by the manufacturer from design specifications. The vehicle was manufactured precisely in the manner in which it was designed to be manufactured. It reached Paul Vance in that condition and was not changed. Ps claim that the weakness of the sheet metal housing upon which the roll bar had been attached was causally related to the trauma to their bodies. When the vehicle landed upside down, the flat sheet metal housing of the rear wheels upon which the roll bar tubing was attached by bolts gave way so that the single, side-to-side bar across the top of the vehicle was displaced to a position twelve inches forward of and fourteen and one-half inches lower than its original configuration relative to the chassis. The housing collapsed, taking the intact tubing with it. D contends that the roll bar was an optional device provided solely as protection for a side-roll. Ps got the verdict and Ds appealed.