Photo: disc and drum brakes of a car (media.vw.com) Author: Konstantin Shirokun
Those drivers who can tell the difference between these two types of brakes often consider drum brakes to be completely unworthy of a modern car. And those who do not have such deep knowledge calmly drive with drums, without any complaints about them. So which type of brakes is better?
Read about whether you should definitely want disc brakes for your car in the RBC-Ukraine article.
Despite all the advances in electronic safety systems that help drivers manage the car's slowdown and braking, each wheel is ultimately stopped by one of two types of brakes – just like half a century ago. These are disc and drum brakes.
Why discs and why drums
So, the mechanisms that brake each of the wheels of the car are of two types – drum and disc. The difference is in the shape of the part that rotates together with the wheel and which is braked by the braking system. In both cases, it is a round working body, which is pressed by the brake shoes. Both the disc and the drum allow the shoes to slip, decreasing this slippage as they slow down – which is, in fact, the essence of any brakes.
Drum brake mechanisms
Drum mechanisms have a cylinder on the hub – the very same drum. It rotates together with the wheel, and from the inside, hydraulics press two pads with force against it. Since the pads, with their pressure, kind of push the cylinder apart, it is made strong, from massive metal, so it turns out to be heavy and expensive. Usually, the drum itself serves for a long time and its cost does not particularly affect. But the extra weight of the unsprung mass of the drum and pads partially worsens the smoothness of the ride. And although designers know how to compensate for these extra few hundred grams by adjusting the shock absorbers and suspension springs, the extra weight on board is not very useful.
In addition, the drum brake mechanism has a whole set of additional parts that ensure the movement of the shoes, and a set of springs that return them to the zero position. On modern cars, drum brakes are used only near the rear wheels, so they also house the parking brake mechanism, which uses the same drum and the same shoes, while having a separate drive.
Among the advantages of “drums” is that their components wear out several times slower than “discs”. Also, the parts of the drum mechanism are simple from the point of view of production, so they are cheaper and more repairable.
Let us repeat that for the last half century drum brakes have been used on passenger cars only on the rear wheels. The reason is that the rear wheels are much less involved in the braking process than the front ones, and the efficiency of drum systems here is quite sufficient.
Disc brakes
The main difference between disc mechanisms is that instead of a drum they have a flat disc, which is compressed on both sides by a pair of pads. The disc has a small metal capacity, it quickly dissipates heat and does not threaten the working fluid to boil from overheating for a longer time. There are no springs or parts that return the pads to the released position. The pads return to their original position under the influence of the elasticity of the rubber cuff, so these systems have high requirements for the condition and cleanliness of the parts.
At first glance, the disk scheme is simpler, but it requires more advanced technologies in production, because there are parts with high dimensional accuracy and units with minimal gaps that are easily damaged – say, due to rust.
When disc mechanisms are used on the rear wheels, a parking brake system is attached to them, which complicates the unit, often significantly – so sometimes, to simplify things, a separate drum is added to the disc – exclusively for the handbrake.
In brief
Yes, disc brakes are more effective under the same conditions compared to drum brakes. However, these conditions are completely different on different cars and even on different axles of the same car. Modern design methods allow designers to easily calculate such a drum mechanism so that it provides the required intensity of braking of the car. And if you do not have a charged sports coupe, but an ordinary family car, rest assured that the standard factory drums (naturally, on the rear axle) will be quite enough for you.
Materials from Autocentre and Motor were used in preparing this article.
Let us recall that RBC-Ukraine recently reported on the types of all-wheel drive available on pickups and SUVs.