One of the most alluring features of Tesla's planned all-electric Model X is its rear "falcon-wing" doors: They open upwards and can thus let people in and out even in a very tight space. Besides that, it's cool, and coolness is Tesla Motors' middle name.
However, as Musk has admitted, coolness comes at a price. Not only would falcon-wing doors prevent owners from mounting a rack on the roof, they are proving devilishly hard to seal against wind and rain.
Why care about a roof rack? Because the Model X is touted as an SUV—one based on the same platform as the Model S but selling for about half the price—and SUVs are meant to port and carry. Still, Tesla can laugh off the lack of a rack because such an add-on not only spoils the line, it also digs into aerodynamic efficiency, which of course is critical in any electric car, given its range limitations.
But there's no laughing off the need to keep the cabin sealed and the rain out. It's all part of a more general carmaking problem known as fit and finish. Poor fit and finish helped to hold back the famous British sports cars of yesteryear, which may have looked every inch the James Bond marvel but weren't much good unless you could stow a Cockney mechanic in the back seat or in the "boot," to fix whatever broke or reattach whatever fell off every few score miles.
Seals are one of the primeval engineering gremlins, and they don't necessarily yield to high-tech solutions. After all, it was a seal, the O-ring, that felled the Space Shuttle Challenger. All this means that the solution will likely come only through normal engineering work, which involves trial and error, and therefore time, and therefore money.
That's just one more reason why Tesla's latest financials show a bump up in R&D expenditure. It's nothing to worry about; R&D is what the company is all about.