Tangent, but what's the rationale for car doors requiring slams? They are the only door I know, at least in common, daily life contexts, that require slamming them with the force of Thor to properly close them.
At a guess it has something to do with needing to withstand 70+ mph winds. There needs to be considerable force holding the door against its seals at all times, and in a mechanical latching system this force must come from a spring, which must be charged with energy via a good slam.
However there are minivans with electronically operated sliding doors, which either power the latch allowing you to gently close the door, or (going further) powering the entire closing operation at a button push. I surmise the reason we see it moreso on minivans is because 1) it is particularly difficult to work up enough energy to properly latch a sliding door, due to losses from the 90-degree change in direction at the end, and 2) violently slamming the sliding doors on a minivan is very dangerous to children's fingers.
It's not about wind pressure. It's that the door when properly closed becomes an integral, load-bearing part of the car's structure. In the event of a crash or rollover, an incompletely-closed door makes the car much weaker and less protective of the occupants.
It's about wind pressure only for doors that have the hinge at the back (I think those also have safety systems that prevent them from being opened while the car is moving). For the more common ones that have the hinge at the front, wind pressure will actually keep the door closed.
I'm not sure I buy this - how is load being transferred through the door? Surely not through the rubber seals, those have minimal shear strength even when compressed. That leaves the hinges, which are certainly robust enough, and the latch, which unless I'm mistaken is only designed to secure the door from opening (usually they engage with some sort of rod or peg, which can't transfer torsional or axial force (i.e. the latch is free to slide along or around the peg).
Luxury cars like MB and BMW also have a soft-close door mechanism for the normal driver and passenger side doors. There's a cam that pulls it in the last few centimeters.
I'm not sure how much money I'd pay for it, but it's a nice feature.
> I surmise the reason we see it moreso on minivans is because 1) it is particularly difficult to work up enough energy to properly latch a sliding door, due to losses from the 90-degree change in direction at the end, and 2) violently slamming the sliding doors on a minivan is very dangerous to children's fingers.
There is also a third, dumber reason, at least for cargo van slide-doors. The surface area of sliding doors are large. When the door takes that 90 degree turn and moves very fast towards the vehicle, it is pushing a lot of air into the vehicle. The air in the vehicle has nowhere to go, so it acts as an air-spring, slowing down the door. To properly latch the door, you have to really slam it hard. If the windows are down or an other door is open, the sliding doors latches very easily. I thought I was going crazy when my door was closing easily ... sometimes. Some cargo vans even have vents that allow air to escape, but people tend to cover them because they don't know what it's for. But electric sliding doors also solve this problem, by moving slowly and letting the air escape.
TLDR: if you car door doesn't close, open the window :)
They rarely require a slam. You can soft-close the door, then lean on the outer edge enough to engage the latch.
Often, the door just isn't aligned correctly. Either it's sagged on it's hinges over time, or the latch itself needs a minor alignment/adjustment (Note that even on a lot of new cars, this still helps a lot! Not all manufacturing is perfect). Other times the rubbers can be hard and perished and it doesn't allow the mechanism to engage properly.
My last two (severely low end) cars had a function that opened slightly one window when there was just one door open,for this reason... To allow the last door to close without excessive force.
On one of the cars it wasnt enabled from factory, but I asked the dealership and they enabled it at no cost.
It's fascinating how doors and windows in a house interact with air pressure. The way doors act when a window is closed versus open, how a half-out-of-frame door will open when a door to the garage on the other end of the house is opened, active central air holding an ajar door against it's frame, etc.
The solidness is an indicator of quality. Apocryphally Mercedes used to add lead weights to their doors to get that solid 'thunk'. Nowadays car manufacturers are a little more subtle at it -- there's a lot of engineering that goes into how a car door feels and sounds to give that impression which is very much intentional.
AFAIK a lot of engineering goes into the hinge to make a car door feel heavy. Meanwhile the average person can easily carry two around without too much effort.
Car doors are unlike any other door in your common, daily life contexts. They are not rectangular. They are heavy and float several inches above the ground. They have hydraulics and/or springs, and typically have two fixed points where they will remain open, even in moderately high winds. They have electronics, power windows, crumple zones, and side airbags. They lock remotely. Their latches and handles are very different from other doors.
A car door is like a bedroom door in the same way a MacBook is like a Cray supercomputer. A door is a door and a computer is a computer, but there is significant variance within that category.
I got a new(used) car which has power closing doors - you just bring them close to the car and the motors gently pull them closed.
Luxury feature because you never slam or even shut the doors anymore, they are closed soundlessly.
I didn't know I wanted the feature till I got this car...now I wish all cars had this. I bet I won't feel the same when I have to pay a thousand dollars to get a single motor replaced.
