When Mike first showed us the Tesla Model X with its Falcon Wing rear doors, I thought oh, this is going to be trouble. These kinds of doors have always been trouble; I remembered that the Gull wing doors (all one piece, unlike the Falcon doors that have an extra hinge and are even more complicated) were the bane of Bricklin owners. They didn't keep out the rain, they didn't open in winter if there was the tiniest bit of frost, they didn't fit in most garages because they went up so high.
And sure enough, they are trouble indeed. According to the Wall Street Journal, they are a serious problem for a lot of owners like the Carters:
On a recent morning, the car’s falcon-wing doors wouldn’t open as she prepared to drive her children’s carpool to school. “It’s a bummer; you spent all this money…and the doors won’t open,” she said in an interview while waiting for the Model X to be picked up for repairs. She expected some issues, but feels embarrassed that friends might think: “Look at the Carters—they spent all this money and the doors don’t work.”
They have been a problem for a while; according to Jalopnik, Tesla is even suing the original door manufacturer "for the company’s inability to engineer the unique and complex “falcon” passenger doors on the electric SUV."
Tesla’s lawsuit claims that Hoerbiger’s design prototypes were riddled with problems, including overheating and oil leaks. The automaker says in the lawsuit that the doors “sagged beyond Tesla’s specified tolerance levels” and “did not open with the speed or symmetry” that it requested.
In fact, the history of gull wing doors should have given Tesla some good reasons to avoid them. Mercedes invented them in 1956 because the design of the car required very high sills that you had to climb up to get over and out of the car. There was no headroom otherwise. But they are hard to engineer, and you had to lift the weight of the door instead of just swinging it.
Then there is the Bricklin, where it is hard to single out the doors as the biggest flaw in this disaster, but certainly added to the weight (which was too much for the engine's power) and the leaking, because according to a Bricklin repair guy, it had "overpowered hydraulic door openers that actually bent the doors during usage."
Gull wing doors are heavy and need some kind of assist to open them. The Delorean had a very clever torsion bar system, but torsion bars are hard to set precisely, and in some cases they actually warped the door to the point that it no longer fit. There is also an issue of safety; doors have to be designed so that they can be opened if the car flips. The Delorean had a window you could push out; the fancy Mercedes AMG actually has explosive bolts to blow the door off in emergencies. Oh, and short people could forget about gull wing doors; they often cannot reach them when they are open.
On Popular Science, Eric Limer concludes:
And ultimately, that's why gullwing doors and their like aren't more widespread: It's just so much easier not to have them. While they do offer a few benefits—and a whole boatload of cool—they cause more trouble (and cost more money) than they're ultimately worth. Most of us don't even know what we're missing anyway. And in the end they don't make it to very many cars, and the ones they wind up on tend towards the expensive.
Gull wing doors were a solution looking for a problem, and Elon Musk has enough problems on his plate without complicating things even further. In the end, they are proving to be an expensive mistake.