Brake know-how: How MTB disc brakes work
BIKE
· 28.01.2023
The most important components of the disc brake
1 brake disc
Brake discs are an easy way to tune the brakes. Small discs with a diameter of 160 millimetres are now almost only used on the rear triangle of race hardtails. With diameters of 180 millimetres, the average biker is well served.
Gravity fans choose discs with a diameter of 200 millimetres or more for more reserves on descents. The material and thickness of the disc also have an influence on the braking power. Two-piece models such as the Icetech from Shimano dissipate heat better with aluminium components. However, they do not offer one hundred per cent protection against fading in the event of overheating. Comparison test MTB disc brakes here >>
2 Brake calliper
The brake pistons are located in the brake calliper and exert pressure on the brake pads and disc from both sides. Four-piston systems have now become established. They work more gently, distribute the pressure over a larger area and usually generate higher braking forces at the limit. The stability of the brake against overheating is also generally higher with four-piston models. The brake fluid serves as a medium to transfer the pressure from the master piston on the brake lever to the slave piston on the brake calliper (brake caliper).
3 brake pads
Friction generates heat. This is why brake pads are made from temperature-stable materials. Special synthetic resin mixtures are used for organic pads. Sintered brake pads are made of metal. The higher the friction coefficient of the pads, the more powerful they are. Some aftermarket brake pads can improve the performance of the braking system.
4 brake handles
Finger exercises are not only on the agenda for piano students. The brake lever allows the braking force to be modulated and more or less finely dosed. The handle first transmits the finger force mechanically via the lever arm of the handle and then hydraulically: inside is the high-pressure pump, a small master piston that generates the brake pressure and sends it to the brake calliper via a pressure line. Integrated into the handle is a small reservoir with an equalising volume that releases brake fluid when the pads wear and the pistons extend further. One finger is sufficient for braking, but you can also use two fingers for powerful braking manoeuvres and prolonged braking on steep terrain. All other fingers should always have a firm grip on the handlebars!
Trouble-shooting brake
Are your brakes squeaking or no longer pulling properly? Don't panic, the causes can often be eliminated with a few simple steps. The best tips for more braking power.
1 Squealing brake
Problem: The brake squeals annoyingly when the brake lever is pulled.
Solution: The reason for this is usually contaminated brake pads. Another side effect is usually poorer braking performance. In the case of minor contamination, it helps to Brake reapplication or sand the pads with fine sandpaper. Afterwards, remove dust and dirt residues with a special brake cleaner. It is best to clean the brake disc at the same time.
2 Change brake fluid
Problem: With new brake fluid, the brake works worse than before.
Solution: Caution! The wrong brake fluid will destroy the brake seals. Some brakes work with mineral oil. Advantage: longer maintenance intervals. Other brake models use DOT brake fluid. It must be replaced once a year on average. DOT and mineral oil differ in their chemical properties. Be sure to check the required brake fluid before changing it.
3 Pressure point
Problem: The brakes only engage when the brake lever is pulled through to the handlebars.
Solution: There can be several reasons for a late or spongy pressure point:
1. The brake pads are worn. Then the oil in the hydraulic reservoir is no longer sufficient to generate enough pressure in the system. If the pads have been braked down to the wear mark on the backing plate, the only thing that can help is a pad change.
2. The width of the brake levers is set too narrow (see Point 4). In this case, increase the grip width with the adjusting screw.
3. Air in the brake system. Special tools are required to bleed the brakes. As the brake is a safety-relevant component, we recommend having it bled in a bike shop.
4 Adjusting the brake lever
Problem: Incorrectly fitted brake levers reduce braking performance and reduce comfort when riding.
Solution: The brakes are often too far out. Loosen the fixing screw and push the levers inwards on the handlebars until you can grip the outer part of the lever with your index finger. This gives you a better lever and allows you to brake more powerfully and more precisely. Adjust the angle of the brake so that the arm and hand form roughly an axis and there is no excessive pressure on the wrist. Use the knurled screw on the brake to adjust the grip width so that the brake lever is parallel to the handlebars at the pressure point.
5 Sliding brake
Problem: Without pulling the brake lever, the brake pads grind lightly on the disc. Constant grinding is usually caused by a warped brake calliper. Irregular grinding noises on the brake may be due to a bent brake disc.
Solution: Overheating or damage during transport can cause the brake disc to bend. It can be straightened again using a special straightening tool into which the edge of the disc is clamped. Be careful not to touch the disc with greasy or oily fingers. To be on the safe side, clean the disc with brake cleaner afterwards.
If the brake grinds permanently, the brake disc is not running through the centre of the brake calliper. In this case, realign the brake calliper. You can read how to do this here:
