Fun Facts about Your Car Brake Caliper’s Placement (Part 4): Roll Center

In the previous sections, we examine one type of factor that determines the location of a car’s brake calipers.

We may have several questions:

1. Is the design of the suspension solely determines the location of the brake caliper?
2. Is one type of the brake layout better than another, from the performance aspect?

Before we diving into these questions, let me first introduce a key concept: the roll center. In this article series the term is for each wheel, it does not mean the roll center of the whole car. Below I am going to explain what the roll center of a car’s wheel is.

For each wheel of a car, it is linked to the car body by the suspension system. The suspension system will define the path of how the wheel will move if the car is going over a speed bump, or driving on an uneven road surface.

Let’s focus on the wheel center: when the wheel moves along with the suspension system, and we mark down its locations (using a dot) in reference to the car body, we can see these little dots form a curve.

We all know if we draw a circle, and cut a section of its boundary, that shape of that section will be an arc (or we can say: a curve). If we properly select the center and also the diameter of the circle, then the “curve” I mentioned in the above paragraph can be completely overlapped onto this circle. Then we say the center of this circle is the roll center of that specific wheel. Please see the following illustration for example.

Please note that the roll center is an abstract, hypothetical point. It does not necessarily be located within the car body; it can be anywhere, depends on the car suspension design. This is similar to the gravity center of a donut, which is exactly in the center; but we all know the center of a donut is hollow and therefore the gravity center of the donut is not located inside the donut.

A typical passenger car has 4 wheels, therefore there are a total of 4 roll centers, one for each wheel. In the next section, I will analyze the brake system from the aspect related to the roll center.

Index

Fun Facts about Your Car Brake Caliper’s Placement (Part 1)
Fun Facts about Your Car Brake Caliper’s Placement (Part 2)
Fun Facts about Your Car Brake Caliper’s Placement (Part 3)
Fun Facts about Your Car Brake Caliper’s Placement (Part 4): Roll Center