Beyond the debates and controversy over their use in high-level competition, disc brakes dominate the cycling market. If you want to brag about having a fully modern bike, it has to have disc brakes.
This guide will tell you all about how they work and current technologies. We’ll also share simple (but effective) tips for caring for and maintaining them.
Table of Contents
Elements and operation of disc brakes, a braking system
Let’s start by reviewing some basics: what are the components that makeup disc brakes? Everything You Need to Know About Disc Brakes
Its construction will differ depending on the hydraulic or mechanical braking circuit. If it is hydraulic, it will have a small reservoir or pump containing brake fluid (mineral or synthetic oil, depending on make or model) inside. Pressure is applied to this fluid using the control on the lever, moving it to activate the brake calipers.
If the circuit is mechanical, there is no pump or reservoir. The same fluid action is achieved through a twisted steel cable, which gains or loses tension depending on how hard the lever is pressed.
Before the fluid directs this pressure to the brake caliper and disc, it flows through the brake hose or cable to the caliper piston. It, in turn, moves to press the brake pads, the other internal component of the brake caliper. Currently, there are two types of stirrups:
- 2 pistons. These are the most common in all disciplines of cycling. The two pistons are behind the corresponding pad on each side of the caliper.
- Of 4 pistons. They are mostly used in the most radical MTB disciplines, such as Enduro or Downhill. However, it is increasingly common to see them in Cross Country, rigid bikes, etc. In this case, the number of pistons is doubled: two on each side of the caliper to apply more braking power with the same or similar modulation.
On each side, the first piston positioned according to the direction of rotation of the disc is smaller than the second. It compensates for the higher braking force exerted in this area. It prevents the brake pad from wearing out more on one side than the other and eliminates disc wobble.
4-piston brake calipers increase stopping power by up to 20%.
Four-piston calipers are larger and about 20-40 grams heavier than two-piston calipers. They are only compatible with specific models of 4-piston brakes and are more expensive: around €50 on average.
When we talk about brake pads, we are talking about the metal part responsible for retaining the rotation of the disc and braking the wheel. It is a piece of equipment with a limited life and must be monitored for frequent wear.
We can distinguish two main types, depending on the lining used for the braking surface: organic (better braking but short-duration) and metallic (braking a little more imperfect but longer duration).
Depending on their size (diameter) and construction (one or two pieces), they will enhance certain properties or others.
1. The diameter of the discs
It determines the braking capacity. A larger rotor will minimize the time between lever actuation and wheel stoppage.
On the other hand, an increase in the diameter of the disc is recommended to cope with the increased power of a particular brake. For example, a four-piston brake will require large diameter discs to cope with that power and handle it better.
Let’s take a look at the different diameters available on the market.
- 140 mm: the smallest standard today. Most often used on road or cyclocross bikes.
- 160 mm: intermediate size, the most used, and the most versatile: cross-country, road, or gravel mountain biking.
- 180 mm: more classic for mountain biking (as a front brake disc) and in disciplines requiring heavy braking: XC/trail or enduro.
- 203 mm: mainly used in the radical disciplines of mountain biking: trail, enduro, and downhill.
- 220 mm: specific disc for enduro and downhill bikes, especially on the front wheel.
A larger diameter rotor tends to minimize the time between when you squeeze the brake lever and when the wheel comes to a stop.
2.- Disc design and construction
Depending on its design and structure, the disc can be heavier or lighter and better withstand the heat and fatigue of braking. In this regard, two categories can be distinguished: rigid discs and floating or two-piece discs.
Rigid discs are made from a single piece of stainless steel. These are the most common, found in entry-level and mid-range bikes. They are also found on high-end bikes, with special designs to dissipate heat.
Floating or two-piece discs have an outer part or braking surface made of steel and a core made of a lighter, heat-resistant material (aluminum or carbon). They are more expensive than rigid discs and are fitted to mid to high-end road and mountain bikes.
On the other hand, it is necessary to consider the type of attachment to the wheel’s hub because there is no universal one, and it is important to determine its compatibility with the bicycle. There are two standards: 6-bolt or 6-bolt (mainly SRAM) and Center Lock (Shimano proprietary standard). Most brands offer models with versions for either system.
Types of disc brakes
Disc brakes can be classified according to two criteria: according to their actuation and according to the cycling discipline.
Depending on their actuation
We have already mentioned that two universal disc brake systems depend on their actuation technology: hydraulic and mechanical.
1.- Hydraulic disc brakes
It is the most widespread system. The brake system is filled with fluid (a mineral or synthetic oil) routed from the lever to the caliper; among its strong points is a more progressive and modulated braking, from less to more, which avoids the wheels locking to promote better control.
2. Mechanical disc brakes
Mechanical disc brakes use a traditional brake cable. Braking is a little more abrupt, less progressive. Also, they tend to misfit and lose feelings. However, repairs and adjustments are simpler than on a hydraulic brake. Eliminate the need to bleed the system and replace fluids.
According to discipline
Another criterion for classifying disc brakes is to consider the type of cycling you do.
1. Mountain Biking
Disc brakes arrived in mountain biking over 20 years ago in response to increasingly technical trails and the need for more efficient and controlled braking. The standard disc brake extends from 160 to 220mm, and the lever is straight and adjustable in reach (no tools are needed on higher models). In addition, it is also possible to improve the power with four-piston models.
The recent road disc brakes have their quirks regarding levers, caliper size, and disc diameter. They are smaller than mountain bike brakes (140 and 160 mm). The floating type is gaining ground on hard brakes, with a more extended and opaque centerpiece and fins that better dissipate heat ( Shimano’s Ice technology ).
Gravel disc brakes have similarities in size and technology to road brakes, using the same type of lever for hook handlebars. But the diameter of the disc is generally larger; we opt for 160 or 180 mm. Also, the brake levers have different designs and ergonomics that allow for better grip while sacrificing weight.
Technologies: new trends
Want to know some of the new technologies that are moving into disc brakes for today’s cycling?
Levers: adjustable in reach and contact
It’s a system on mountain disc brakes, like the SRAM G2. In addition to the more usual adjustment of the position of the lever relative to the handlebars (using a small wheel), another wheel or dial integrated into the body of the lever makes it possible to adjust the point of contact with the brake pad. It influences the mechanism’s travel, making it possible to obtain a firmer or softer feeling without modifying the position of the pads.
Calipers: four-piston and rigid
Brakes with four-piston calipers have broken the boundaries of competition and extreme mountain biking. The major brands now offer models for all types of mountain bikes and in all price ranges.
The emergence of electric bicycles, which require more powerful brakes, has also contributed to this expansion. The calipers feature designs that provide greater integration and stiffness, promoting smooth vibration-free braking and preventing caliper movement or misalignment.
Mounting: Flat Mount
The front and rear brake calipers of many medium and high-end bikes, both road and MTB, are already fixed with the Flat Mount system. It is thus possible to dispense with the adapter of the caliper to fix it to the Post Mount frame, which saves a few grams, obtaining better integration into the bike and greater rigidity in the braking area.
Cooling of calipers and discs
Disc brake overheating from continuous use (especially downhill) leads to system fatigue, loss of feeling, and loss of power. Manufacturers are constantly working on technologies to better dissipate heat from discs and calipers, where the temperature rises the most.
In calipers, aluminum pistons are gaining ground as a solution to overheating.
Shimano has perfected its Ice technology, now called Ice Freeza, for its most advanced brakes (Dura-Ace, Ultegra, XT in MTB, etc.). It focuses mainly on the discs, adding in the central part steel or aluminum fins (depending on the model) that dissipate the heat.
It also adds a thin layer of aluminum to the body and the brake track. This material retains less heat than steel, as well as a special paint as a coating, capable of reducing the temperature by 10ºC.
For its part, SRAM launched its HS2 discs for mountain bikes in 2021. They are of the floating type and have the particularity of having rims with a special black paint coating that manages to lower the temperature up to 40ºC in the most demanding braking conditions.
Likewise, increasing the disc’s thickness from 1.85 to 2mm in this case always reduces heating due to the use of more material.
Maintenance: basic maintenance to avoid breakdowns
Bleeding the fluid is one of the most important operations for proper disc brake maintenance, not forgetting the replacement of the pads.
It should be done once a year, whether you use your bike a lot or not. Brake fluid loses its properties with and without use, so it will be necessary to remove the old fluid by injecting new fluid through the lever into the caliper outlet.
At first glance, this is a simple operation you can do at home, but you will need two small tubs, a funnel, and some brake fluid to perform the bleeding.
Replacement of pads
The lining of the brake pads is removed by friction with the disc. Its condition should be checked frequently, every two or three months. If its thickness is less than 1 mm, you must consider replacing it; if its thickness is less than 0.5 mm, you must replace it immediately because the metal support of the pad (harder) will start to rub against the disc, which will damage its braking track.
You can disassemble the caliper and remove the pair of pads using the metal bridge to check the wear of the lining. This operation can be carried out at the same time as the annual bleeding to organize the maintenance of your brakes better. The pad cost is not very high, since it is between 10 and 20 euros. You can change them at home without too much trouble, saving you a lot of money on shop labor.
Harsh braking, shocks or falls, or simple use, can cause misalignment of the caliper mounting on the frame or the fork (in the case of the front brake). The pads are therefore off-center about the disc, which generates friction even when the brake is not activated.
To avoid the annoying noise it generates and to reduce the wear of the pad due to this friction, loosen the caliper retaining bolts. Move it and center it slightly while squeezing the lever to realign it with the disc, and tighten the bolts again, alternating this tightening so that it is even on both sides.
Cleaning: calipers, pads, and discs
Brakes with discs, calipers, and levers cleaned before each ride will work more efficiently and extend their life. After each ride, superficial cleaning with soap and water, avoiding getting inside the stirrup, is essential.
To clean the inside of the caliper, which should be done monthly, you must first remove the pads. Then clean the inside with water, neutral soap, or a specific cleaner for disc brakes. Finally, lubricate the surface of the pistons with the same brake fluid as the circuits.
Disc brakes should be checked thoroughly yearly, and the fluid and pads should be replaced.
As for the pads, check that the lining is free of dirt, oil, etc. Otherwise, they will be contaminated and need to be treated with water and alcohol, then lightly sanded to remove these residues. Failure to follow this instruction compromises braking efficiency and braking feel.
Cleaning the disc brake track is also essential. Do this after each trip with a soft cloth (microfibre), a little water, and neutral soap. There are also record cleaners on the market with dust or sludge removal properties.
Don’t forget to carry out a preliminary test.
Finally, some advice for cyclists who are unfamiliar with disc brakes.
First, the braking’s feel, power, and modulation are different from that of a shoe brake. Prior adaptation and training are therefore necessary.
In this sense, when buying a new bicycle equipped with disc brakes, or after each change of brake pads, a process of trial or acclimatization to the system is necessary. Because the lining surface of new pads is so firm and polished, the pads will slip on the disc and not stop it, increasing the risk of an accident.
After each pad change, it is advisable to carry out an adaptation procedure on the bike.
You have to pedal and touch the brake less and less hard repeatedly, on a flat road or a street without heavy traffic, in a controlled manner. We recommend doing this until you feel the feeling hardening and the bike coming to a stop faster and faster. You can also do this while stationary, putting the bike on one foot with the wheel hanging in the air and repeatedly braking until it hardens.
It also ensures that the pads are aligned with the disc and wear evenly across the entire disc surface.