What is an "A pillar"?

Question

I hear the term thrown around a lot about the A pillar or B pillar ...

• What are these and of what importance are they?
• Are there any other pillars in a vehicle?
• Do all vehicles have all the pillars?

Answer 1

Pillars are vertical supports on a vehicle. They are located around all the glass on an automobile. They are important for holding glass in place and adding structural integrity to a vehicle, primarily the roof.

The "A" pillar holds the windshield in place. Take a look at this representation.

"B" pillars start at the end of the first door. They usually offer substantial structural support for a vehicle's roof. Most of the time they are bound to the body frame and wrap all the way into the roof. Depending on the design, there may be multiple pieces attached to increase the integrity of the roof. They are also responsible for where a door's latch connects to the body.

"C" pillars hold a vehicle's rear window in place.

Not all vehicles share the same number of pillars. For instance, early Hardtop coupes lack a B pillar.

Here is an example of a Pontiac from the '60s. As you can see, it only has an A and C pillar in its design.

Limos can have upwards of 5 pillars or more depending on their length.

Here is an example of how one might be constructed.

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Convertibles use pillars but to my knowledge they are not called "A" pillars (unless a specific modification was done to a vehicle, ie. Ford Sport Coupes inspired by the Ford Roadster, hence "Coupester").

Here is an example of Mustang convertible pillars.

Answer 2

What is a Pillar

There are three main types of pillar when referring to the design of a car - A, B and C. The A pillars on your car hold either side of the front windscreen in place. They are the ones you see as you look straight at the car from the front. B pillars start where the driver and passenger-side windows end as you look backward along the length of the car. C pillars hold the sides of your car's rear window in place.

Note: Some cars also have a D pillar, such as estate cars for example. D pillars hold the sides of the rear window of the car in place and can also sometimes serve as a housing for the rear lights like indicators, brakes and alike.

Why They Are Important

Without pillars, the glass on its own would not be able to support the weight of the cars roof. They provide a firm structure to the top of the car so that you can roll your car windows down, or even carry weight (usually up to around 100kg on most modern cars) on the roof using something like a roof rack. They provide a good base for the windows for the car to be installed.

Also, another point is that if you have a center console on the roof of your car, such as a light or electric sunroof controls then all of the cables for these interior luxuries must be routes through one of the pillars (normally the A pillar, but again this depends on the car).

Do All Cars Have Pillars?

No. For any car that doesn't have a roof, there is no need to have pillars to support anything. A Caterham (small sports car without a roof) is a good example of this as many of them do not come with a roof.

Answer 3

The pillars are what connect the sides of the car to the roof. Convertibles are the only cars I'm aware of that don't have what could be considered pillars.

The pillars separated into driver side and passenger side. The very forward pillar is A, the next one is B and so on.

For example driver side A pillar is the forward most pillar on the driver side.

The plastic covers are commonly used to route wires and other things. If the car has a sun roof the A pillars have drains in them. The B pillars commonly contain the front occupants seat belts.