Actually, in the Z1 the high sills offer sufficient crash protection to allow the vehicle to be legally driven with the doors open. The vertical doors they use are designed to strengthen the chassis. A convertible will generally always have lower chassis rigidity than an equivalent coupe. However the lack of roof makes the door openings in a convertible particularly weak, which is why many convertibles and T tops are known to have bending of the frame rails when they are jacked unevenly. The high side rails reduce the effective size of the “hole” in the chassis and act to brace it. While a half door of a conventional design or a hardtop with true half height gull wings woukd likely be stiffer- it is by nature a convertible and will not be as stiff as it could be even with generous bracing. One should buy a 5 or 7 series if they are extremely concerned about the issue, but this design offers adequate protection. BMW didnt get so big by murdering the people able to pay for their cars...
.... they tend to do a very good job keeping their customers alive and happy to buy another car- and they generally are engineered to perform well compared to other vehicles in their segment when it comes to crash safety.
Sorry I just picture my clutz ass putting stuff into he car and pushing the button not aware it isn't all the way down and tripping on the door and falling flat on my ass. Maybe even cutting my legs by braking my fat ass on the window. So this is truly amazing I just don't think I want my car door to do that.
Bavarian
Motor
Witchcraft.