clearance (horizontal and vertical) than would otherwise be required. The vehicle also has sensors to determine ceiling height and the presence of potential obstacles and to determine how the hinges will operate to open the doors and avoid obstacles, if possible. Design challenges Gull-wing doors have a somewhat questionable reputation because of early examples like the Mercedes and the Bricklin. The 300 SL needed the door design, as its tubular frame race car chassis design had a very high door sill, which in combination with a low roof would make a standard door opening very low and small. The Mercedes engineers solved the problem by also opening a part of the roof. The Bricklin was a more conventionally sized door but the actuation system was problematic in day-to-day use and led to unreliable operation until an aftermarket air-door upgrade was installed in all Bricklins. In addition, there was some concern that in making the doors as light as possible they wouldn't provide adequate protection in side-impact accidents. There was, however, no indication that this concern was justified. The DeLorean solved these problems by using a patented cryogenically-set stainless steel torsion bar spring (manufactured by Grumman Aircraft Engineering Corporation) to partially counterbalance a full-sized door, and then added a gas-pressurized (pneumatic) strut similar to those found in hatchback cars. The combination of the torsion spring and strut provided the correct torque variation necessary to offset the variable torque of the door, as it opened through a rotational angle of about 80 degrees. The torsion bar is most important in the first foot of movement from the bottom, where the geometry of the strut is pointed at the hinge and therefore at a mechanical disadvantage. As the spring relaxes through the door's rotation open, the strut gains a better moment arm and gradually takes over the effort. A correctly balanced door opens fully on its own by simply activating the door latch from the interior, exterior, or from an aftermarket wireless release. Other disadvantages of the system were not so easy to address. For example, the gull-wing design makes creating a convertible version of the car harder, as the hinges would be removed with the roof, and standard doors would be needed for the convertible. Mercedes did so when replacing the gullwing coupe altogether with the 300SL roadster in 1958. It was never a concern for DeLorean, since no convertible version was