For a long time, bicycles have used a very traditional type of brakes. These are known as the rim brakes, and nearly every road bike (see all our reviews) and mountain bike (see all our reviews) has had them (and still does).
They work by means of a rubber brake pad that is just over the rim of the front and back wheels. When the brake lever is squeezed, the pad pushes against the side of the rim, generating enough friction to slow the bike down and bring it to a halt.
The Disadvantages of Standard Rim Brakes
Rim brakes have the chance of failing under high levels of stress though. While rim brakes have been tried and tested over and over again in a number of different applications, it can’t be denied that they have the chance to fail.
At high speeds, applying the rim brake is likely to cause a lot of friction with the wheel. This will lead to a high level of heat being generated, causing the rubber in the brake pad to wear out faster. You do not want to find out that your brake pad is worn out while freewheeling down a steep gradient.
Another bad thing about the standard rim brake is that it cannot last long under different environmental conditions. For example, while riding through muddy terrain, the rim can collect a lot of slick, wet mud. If you squeeze the rim brakes while the rims are muddy, it could result in slipping, and could cause accidents very fast.
Entering the world of the Disc Brake
The solution to this is a fairly innovative new technology for bikes at least. The disc brake has been around for cars for a very long time. How it works is that there is a metal disc connected to the wheel hub. This disc is usually slim and lightweight, and has holes drilled in it at intervals. These act as a heat sink for any friction related heat generated during the braking process.
The disc rotates with the wheel. Calipers are attached to the fork of the bike, and they have brake pads on them. When the brakes are applied, the calipers squeeze the pads against the disc instead of the rim. This causes the kinetic energy of the bike to be converted to heat energy. According to the principle of conservation of energy, the amount of kinetic energy lost is equal to the heat energy generated.
This means that if all the kinetic energy the bike possesses is converted to heat, the bike will come to a complete standstill. It is just basic physics. Now, it may seem to you that the disc brake’s operation is exactly the same as rim brakes. Basically, this is true. They operate on the same principle. Friction has always been the best way to stop a moving object.
The Perks of using Disc Brakes
However, there are certain undeniable advantages of a disc brake over the normal, standard rim brakes. Some of these include:
- Strong action – The calipers are far more effective than the standard rim brakes. This is because they are larger than the rim pad, which is usually a 3 x 0.5 inch rubber pad on either side of the rim.The calipers however have a larger surface area than this, allowing them to convert more kinetic energy into heat in a given time without heating up as much. This means that they are far faster in slowing down and bringing a bike to a quick halt.
- All-terrain effectiveness – One of the biggest perks of using a disc brake is its effectiveness in any type of terrain. Usually, rim brakes would not work in conditions such as mud and water as effectively as they do on dry roads. In a world that is increasingly affected by random thunderstorms and wet weather, you need a guarantee that your ride will be a safe one in any weather conditions.A disc brake can help with this because it is not as exposed to the water and mud during wet weather. This means that it can stop the bike with nearly the same efficiency as it would in normal weather conditions. This is great for all you cyclists living in area with mud or rainy weather as well.
- Rims do not affect performance – In a rim brake, a big problem is that the effectiveness of the brake pad depends on the state of the rim. In extreme weather conditions, or due to cycling on roads with a lot of potholes and bumps, rims tend to become warped and disfigured. The brake pads on rim brakes will then stop generating constant friction against the warped rims.However, this is not a big concern when it comes to the disc brake. Owing to its independent placement with the wheel, the disc has a far lower chance of being affected by such things as warping.
- Endurance – Compared to rim brakes, disc brake pads have a larger surface area. This means that when they are in contact with the disc, they generate heat, but not nearly as much as the rim pad does. This is because rate of energy generated is proportional to the area over which it is generated. Higher area – higher rate of energy transferBecause of this, the disc brake pads tend to wear out at a far slower rate than their rim counterparts. This allows for a reduction in replacement costs as well as increasing their safety.
- Lower chance of flat tires – One of the biggest disadvantages of rim brakes, especially in hot, sunny climates is the excessive amount of heat generated. Just try touching your rims immediately after a long braking action. It will be hot enough to fry eggs on. This overheating of the rims can cause tires to blowout because the heat can cause the rubber in the tires to weaken.The disc brake is not connected to the rim in any way. It is an extension of the wheel hub. Because of this, the disc may generate heat, but it doesn’t affect the rim in any way whatsoever. This greatly reduces the chances of overheating and tire blowouts in hot climates or during extreme cycling conditions.
- Reduced wear and tear – The disc brake doesn’t wear out the rims over a long period of time. This is a common problem in most bikes with rim brakes. It is usually most obvious in rims made out of carbon fiber composite materials that have been made for lightness. The high amounts of heat generated will definitely weaken the material and cause the area that has been exposed to the brake pads to become thinner than the rest, like a groove.
- Increased versatility – One of the biggest advantages to the disc brake is the fact that the brake pad doesn’t depend on the size of the rim. You could replace the wheel with a differently sized one depending on the conditions you want to cycle in without having to change the size of the disc brake calipers.
The History of the Disc Brake
In 1997, Hayes Mag was the first proper disc brake to be introduced for bicycles. It set the template for the standard disc brake that is now popular all over the world.
The disc brake wasn’t that well accepted for a while though. This was because bikes weren’t made with disc brake mounts, since the rim brake was the accepted standard.
People were being rather ignorant about the fact that disc brakes were going to be very useful, both for safety reasons and for stopping power. However, a lot of smaller racing brands began using the new disc brakes. In 1999, Trek and Gary Fisher endorsed the disc brakes, fitting them to their 8900 and X-Caliber bikes.
This sent a strong message to the people who were doubting the effectiveness of the innovative new disc brakes. Soon, larger companies began to inquire about these brakes.
Soon enough, the bike racing and parts greats like Shimano and Magura began producing early versions of the new disc brake technology, and completely changed the world of cycling forever.
In recent years, disc brakes have made an emergence into the field of road bike racing. These competitions happen with bikes going at about 80kmph, and there are a lot of safety concerns at such high speeds. Rim brakes just aren’t doing it anymore.
Types of Disc Brakes on the market
There are two types of disc brakes in the current market, each with its own features. These are:
- Hydraulically actuated disc brakes – The brake lever being pulled causes a piston to push fluid (typically ethylene glycol, commonly called brake fluid) down, causing the calipers to engage with the disc actual.
- Mechanically actuated disc brakes – these are the more common type of disc brakes right now, using the traditional mechanism of brake cables to engage the calipers.
Mechanical disc brakes are more popular mainly because they make use of traditional brake cables. People find this more comforting because it is an age old technology that everyone is familiar with. This makes maintenance and replacement of parts easier.
However, hydraulic brakes are becoming more common on endurance bikes, where brakes are used a lot with the finest adjustments made to the amount of pressure applied to the brakes. Hydraulic actuation systems are always better at fine control of pressure applied.
Mechanical disc brakes are what you would usually choose though. In addition to them being easier to maintain, the mechanical systems are cheaper than the newer hydraulic ones, because they employ older technology. In addition to this, hydraulic systems add extra weight to the bike.
This can be a problem to most cyclists, who prefer lighter, speedier bikes for road use. Because of this the mechanical cable actuation system is far more desired in the current generation, in keeping with tradition and with speed.