Car design help!

I am not in industrial design major, but I have a question about car design.

I have a question on why there are those elongated budges, that looks like stripes on some cars. Sometimes the stripes are located higher on the car:

Also, for having smaller roofs, is it purely for reducing drag (the question on the image is missing the word ‘drag’ after ‘less’. It originally said: Does a smaller roof produce less drag)?

The car below is different from the one above. The one below is by Ford, and as you can see, it is missing the stripe prevalent in the above picture. Why?

  1. Strips are trim for preventing your door getting banged in a parking lot

  2. Smaller roof might have something to do with aerodynamics but is more like a design choice related to the profile and DLO (day light opening =windows) the designer wants.


  1. The strips are also there because of manufacturing. It wasn’t until recently, maybe the last 10 years, that manufacturers could stamp consistently high-quality doors with large flat surfaces that would be strong enough to take minor bumps. The stamping where they apply the strips helps to rigidify the surface.

  2. By smaller roof, do you mean shorter glass? If so, it is purely for styling reasons. Aerodynamics is a mix of drag coefficient and frontal area. If anything, frontal area has been increasing for years.

My question is why are the painted stripes there?

My answer is that they are a cheap way to make the car more horizontal, which we associate with feeling faster. It’d be much nicer if the forms we faster to begin with, though.

Thanks for the answer! Okay, now I found some more cars with different designs for the side, and I am more confused here:

  1. There is actually a groove on the Ford Escape Hybrid. I am guessing it doesn’t protect bumping against doors, so what is it for?

  1. This next one is BMW X-Drive, which as a sharp obtrusion through the door handle. Since I don’t see these sharp trims or bumps in too many cars, my question how does this sharp obtrusion affect the aerodynamics?:

  1. I have another question regarding the back part here, how does this particular thing affect the aerodynamics?

  1. My last question regards those small slanted objects on the roof of cars. I don’t really know what is it called. How does this little thing here affect aerodynamics?

Thank you guys SOOOO much for answering, you don’t know how helpful this is to me! If I had an industrial design course that is design oriented around my area, I would not be asking so much questions. Unfortunately, the only industrial design course around my area is engineer oriented. So thanks again for the replies! If you guys can also recommend some beginner industrial design books, so I don’t have to ask so many questions, that would be great!

I’ll let others who are more well-versed in cars answer these, but I’m pretty sure what you’ve circled in the last image is the antenna.

The spoiler does create some amount of drag (slowing the car down…) but makes up for it in down force to the rear tires. Without that, you’d lose control at speed in that particular vehicle because of it’s powerful engine. Many cars have spoilers and are purely cosmetic, for the most part.

1: It’s a style line but increases rigidity at the bottom of the door. Go to a local hardware store and buy a cheap roll of sheet metal and cut a piece off. It’s incredibly flimsy. As soon as you put a crease through it, it becomes very very stiff in that direction because that ridge adds structure. The stick on bumpers shown in the first picture are purely for bump protection - they are usually pieces of plastic stuck on with double side tape.

2: The sharp protrusion on the side probably does almost nothing for aerodynamics. Cars drive head first into the wind, which means the frontal cross section is what is important. Since the sides are relatively flush and the same profile, air will move past it without issues.

3: Spoilers add downforce if they are designed to. This increases traction to the rear wheels at high speed. This is why all race cars generally have giant spoilers. On something like a front wheel drive Honda, the spoiler does nothing but add decoration since they are actually providing downforce to the wheels that don’t need it.

4: That little shark fin is an antenna assembly - generally for cars with Satellite Radio, but some cars will use it for the FM or GPS antennas as well. No real impact to aerodynamics. It’s a smooth object that creates very little drag. However sometimes you will see cars (Take a look at a Mitsubishi Lancer Evolution MR) that has a row of these shark fins which actually act to generate a vortex behind the car. Theirs also Venturi diffusers (under the back bumper usually) to reduce underbody drag, etc.

Lots of stuff on Aerodynamics out there if you are interested. Look up info on formula 1 cars, air brakes, etc.

… both of the police cars posted are made by Ford.

Since most of your questions seem to be focused on asking about aerodynamics I’ll answer the only question more thoroughly than anyone else has that’s the only thing really related to aerodynamics that you’ve been asking about.
#3 - Spoiler
For basics: a spoiler is the opposite of an airplane wing. Obviously, a car performs best when it’s wheels are on the ground; and vice versa a plane works best when in the air. So, because an airplane wing helps lift in aerodynamics, a spoiler creates down-force to keep the wheels planted on the ground.
More In-Depth: first, a spoiler is only effective in sports cars at high speeds. Like previously stated many standard vehicles have them for aesthetic reasons as well (there’s also some other reasons for non-sportcars to have them besides aesthetics, I’ll explain later) but the main reason for the spoiler is to create down-force. Why do you need down-force? Because the faster your vehicle travels, the more likely it is to “lift” from the ground, so it’s very essential in many cases. Secondly, for the spoiler to have any positive effect on a vehicle, the vehicle needs to be RWD, because the down-force created by the spoiler puts the the rear wheels on the ground, not the front (unless you have a front spoiler) wheels. Now, with all that being said… not all spoilers are effective. Some will make the handling worse than a vehicle without one, it’s an essential test that needs to be done to see if the handling is effected positively or not in high-end sports cars that rely on a spoiler.
Now, going back to other reasons a spoiler is used, not as a primary function of handling/down-force. Having a rear spoiler in the back of a passenger vehicle can have such benefits as better MPG/decrease drag and a simple effect such as keeping the back window cleaner. Why? Because like the sports cars, spoilers in passenger vehicles redirect the airflow over the car, making the “airflow line” a more straight path over the rear-end.

Now, with all that being said… this information is also all over the place, searching here, google, etc… and reading would answer your questions and be far more efficient and you’d learn much more most likely.

I like the honesty shown by the OP here!

“The only stupid question is the one you don’t ask” and all that!