If disc brakes are better, why do modern cars still have drum brakes?

Arif · Jul 07, 2020 01:47 PM

All variants of the Perodua Myvi have rear drum brakes. The same goes for the current line-up of the Honda City. The Toyota Vios, on the other hand, has rear solid disc brakes for the “G” variant, but the remaining “E” and “J” variant come with rear drum brakes. Often seen as a “poverty spec” feature, drum brakes are still prevalent in modern cars of today.

A spoon brake on a Penny-Farthing bicycle is ancient.

Before we start calling drum brakes ancient, it is important to note that ideas for both drum and disc brake types were conceived in the early 20th century. However, disc brakes supersede drum brakes in terms of stopping ability and heat dissipation.

Glowing disc brake rotor. Image source

Disc brakes are often associated with high performance, and it is absolutely right to do that.  As pre-adult car enthusiasts, we loved the sight of glowing brake rotors that sometimes turned green, yellow, or red depending on the rotor temperature.

Red brake calliper covers neither improve braking performance nor increase horsepower

Besides the high performance of disc brakes, its aesthetics was also widely appreciated by car enthusiasts around the world. Red brake callipers gained massive popularity and spawned various attempts to emulate the look with painted callipers or even brake calliper covers.

Jesse's Jetta was living in 3029 using ventilated disc brakes with calliper delete.

It is obvious that disc brakes work better. To understand why, we first have to understand how these things work. Let’s get into the technicalities…

Q: What do drum brakes and disc brakes look like?

A: Like this:

Q: How does a drum brake work?

A: By wedging the drum with the brake shoe. This is how it looks like inside a drum brake. Drum brakes are self-energizing which means it will lock the wheel even harder if the wheel tries to roll.

Drum brake mechanism. Photo: Blue Pigeons

Q: How does a disc brake work?

A: By clamping the brake rotor using the brake calliper.

Disc brake mechanism. Photo: Mechanical Booster

Q: What are the advantages of disc brakes?

1. Better at slowing the car down.

2. Better heat dissipation. Thanks to the large open surface are of the brake rotor.

3. Disc brakes are less likely to trap water. Thanks to the open design of disc brakes as opposed to the closed design of a drum brake.

4. Disc brakes are less likely to trap dust. Thanks to the open design as opposed to the drum brakes. This is also why your front wheels get covered in more dust than your rear wheels.

Front wheels are usually covered in brake dust.

Q: Does ABS only work with disc brakes?

A: No. Both disc and drum are usable with ABS.

Q: Does having rear drum brakes mean my car doesn’t stop well?

A: Disc brakes stop the car better than drum brakes. However, for standard daily driving, having rear disc brakes does not give any significant advantage.  Most of the stopping work is done by the front brakes anyway. By the way, practising the correct method of engine braking could extend the service life of your brakes.

Massive disc brakes used for trucks.

Q: So why are drum brakes still used in modern cars?

1. Manufacturing. Drum brakes are cheaper to make and double as a parking brake. Cars with all around disc brakes require an extra brake to function as the parking brake.

2. Safety (Parking). Drum brakes lock-up the wheels easier and make better parking brakes than disc brakes. Those who enjoy doing handbrake turns may also favour rear drum brakes since they lock-up easier (self-energizing).

3. Drum brakes are also smaller and lighter but these are not reasons why modern cars still use them.

Rear drum brakes on a Ford Fiesta EcoBoost.

In summary, disc brakes do a better job at slowing the car down. High performance cars and even huge trucks use disc brakes. However, drum brakes do a better job at locking the wheels.

Parts inside a drum brake.

Modern lightweight cars still have rear drum brakes since the majority of the stopping work is done by the front brakes. Although perceived as "ancient", drum brakes are sufficient for everyday driving and are easier to produce. To know how you can inspect your brakes without the use of tools, click here.