In this section, let’s take a look at one factor that determines the location of your car’s brake calipers.
First, we look at the front wheels. You may find many front-wheel-drive cars have their front brake calipers in front of the axle, that is because for FWD layout, the engine is usually transversely placed in front of the axle. With such layout, the steering arm can not be placed in front of the axle because the transversely placed engine acts like a wall to block the passage of the steering shaft. Therefore, the steering arm can only be located after the axle, which means there is no place left for the brake system at the same location. So it is very common that FWD cars has the front wheel brake caliper in front of the axle.
You can see how the engine block the steering shaft, in the below illustration for the Volkswagen GTI.
Here is how the GTI drivetrain looks like when viewing from above.
For rear-wheel-drive layout, that is another story. Most of the RWD cars place the engine in front (except some exotic sports cars which are mid/rear engine layout), and their engines are in longitude position. Usually the cylinder block is either V-shaped or I-shaped, and it leaves enough space below the cylinder banks such that the steering shaft can go through. Therefore most RWD layout cars has the steering arm in front of the axle, and the front wheel brakes are behind the axle. You can see the below Lexus GS350 underbody photo as a reference.
But there are always exceptions. Not all RWD cars put the front brake after the axle, and the reason varies. For example, the Nissan GT-R locates the front brake in front of the axle, that is for brake disc ventilation consideration; since the GT-R will see many track usage which puts heavy loads on the brake system. The same reason applies to the Porsche Cayenne.
Another example is the Scion FR-S/Subaru BRZ, it also places the front brake in front of the axle. But its reason is similar to FWD layout: the engine blocks the steering shaft. How come this happen on a RWD car? That is because the FR-S/BRZ is using the flat-4 boxer engine, whose cylinder banks is not a V-shape, but with a 180-degree angle, and it ooks like “_ _”. The advantage of this design is its low gravity center, which benefits the car’s handling. But this comes with an expense: there is no enough space under the cylinder banks which a V-shaped engine has, to let the steering shaft pass through. Therefore, the FR-S/BRZ designers have to place the steering arm behind the axle, next to the rear end of the engine. You can see the below photo to help you understand this.
In part 3 of this article, I will examine the rear wheel brakes.
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
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