In the world of car design there’s a basic idea that rules everything: Form follows function.
This means that the form of an element in a car is determined by the function the car or the element itself must accomplish.
Up next we have some examples:
Family car must carry four or five occupants (green) with relative comfort. That’s why the cabin must be roomy.
Trucks must be big to carry lots of stuff at the back, obviously. But also the must to able to go through some really rough terrain, hence the ground clearance and the wheel housings (red).
Of course, this is useless if the suspension isn’t adequate to go over rocks or speed bumps. For this to be possible the suspension must have enough travel (green). We’re not going to draw the suspension but it is a good example.
Sports cars must have good balance in corners, that’s why the engine is at the back (red). Keep in mind that there are front engine sports cars but generally they aren’t as effective as mid-engine cars.
The must manage the air passing around them (blue) better than most cars so they have as little wind resistance as possible. That’s why they are very low and the passengers are closer to the ground and in a more leaned back position (green). This gives them a small frontal area.
So, next time you are making a car drawing take into account what it’s supposed to do and design it from that basis.