Disc brakes

Key facts

Standard

Post Mount and Flat Mount calipers; 6-bolt and Center Lock rotors

Service interval

bleed once a year; pads at about 1 mm of lining

How they work

Pulling the lever pushes fluid down a hose to the caliper, where pistons press two pads onto the rotor. Because the fluid does not compress, a small movement at the lever becomes a big clamping force — and the power is easy to dose.

Choosing

• Two or four pistons. Two-piston brakes are light and enough for cross-country; four pistons give more power and a calmer bite for trail, enduro and eMTB.
• Rotor size. 160–180 mm for light riding, 200–220 mm for long descents, heavy riders and e-bikes. A bigger rotor brakes harder and runs cooler.
• Pads. Organic pads are quiet and bite well when cold; sintered pads last longer and cope with heat and wet.

Fluid

Brakes use either mineral oil or DOT fluid, never both — the wrong one destroys the seals. The fluid is printed on the lever or caliper. A spongy lever that pulls to the bar means it is time to bleed.

Bed them in

New pads and rotors need bedding in: twenty or so firm stops from moderate speed, without locking the wheel. It lays pad material onto the rotor and can double the power.

Related articles

• SRAM — An American component maker from Chicago, founded in 1987. It made the 1x mountain drivetrain mainstream and owns RockShox, Zipp and Quarq.
• Shimano — A Japanese maker of bicycle components founded in 1921 in Sakai. Its drivetrains and brakes are on more bikes than any other brand's.
• Downhill (DH) — Racing one steep, rough track from top to bottom, against the clock, on bikes with around 200 mm of travel. A World Cup run lasts three to four minutes and is decided by fractions of a second.
• Pre-ride check — Five minutes before every ride that catch most mechanicals before they happen: tyres, brakes, axles, bars and the drivetrain, checked in one pass around the bike.
• Brake bleed — Replacing the fluid in a hydraulic brake and pushing out the air bubbles that make the lever soft. Once a year, or whenever the lever feels spongy or pulls to the bar.
• Braking — Braking well is braking in the right place: hard and early on good ground, then off the brakes where the trail is rough or turning. The front brake does most of the work.