Bike Brake Glossary: Rotors, Calipers, Pads and Bleeding

A brake in which a caliper squeezes pads against a rotor bolted to the hub. It stops almost as well in the wet as in the dry and doesn't wear the rim; today it's the standard on mountain, gravel and nearly all road bikes.

See also: brake rotor, brake caliper, brake pads, hydraulic brake

A brake that squeezes pads against the sides of the rim. It's light, cheap and easy to adjust, but loses a lot of power in the rain and wears the rim over time.

See also: brake pads (rim), V-brake, caliper rim brake

The steel disc the pads bite on. Typical sizes are 140 or 160 mm on road and gravel bikes and 180-203 mm on mountain bikes and e-bikes: a bigger diameter means more power and less heat.

See also: Center Lock / 6-bolt, caliper adapter, brake fade

The part that straddles the rotor and houses the pistons that push the pads. Two-piston calipers are enough for road and XC; four-piston calipers give more power on long descents and on e-bikes.

See also: piston, brake pads, Flat Mount / Post Mount

The plunger in the caliper that the fluid pushes to move the pad toward the rotor. If one piston comes out less than the other, the pad rubs: clean them and carefully push them back in to reset them.

See also: brake caliper, hydraulic brake

Plates with friction material that bite the rotor. Each caliper uses a specific pad shape, and you replace them when about half a millimeter of friction material is left.

See also: organic (resin) pads, sintered (metallic) pads, glazed pads

Resin pads: they bite well when cold, are quiet and are gentle on the rotor, but they wear faster and heat up sooner on long descents or in mud.

See also: brake pads, sintered (metallic) pads

Pads made of pressed metal particles. They handle heat, water and mud better and last longer, at the cost of more noise and a less refined feel when cold.

See also: brake pads, organic (resin) pads, brake fade

The rubber blocks on rim brakes. They have grooves that show wear: when the grooves are gone, it's time to replace them. Carbon rims need specific pads.

See also: rim brake, V-brake

The handlebar lever that operates the brake. In the US and Spain, by convention, the right lever works the rear brake and the left the front; in the UK and Australia it's usually the other way around.

See also: reach adjustment, bite point, brifter (shift/brake lever)

A brake that transmits force from the lever to the caliper through fluid. It takes little finger force, self-adjusts as the pads wear and needs bleeding from time to time.

See also: brake hose, brake bleed, mineral oil, DOT brake fluid

A cable-actuated disc brake, like a rim brake. It's cheaper and easier to fix on the trail, but has less power and you have to adjust the pads in by hand as they wear.

See also: hydraulic brake, cable housing

The flexible line that carries fluid from the lever to the caliper on a hydraulic brake. If you shorten it, you need a new olive and insert, then bleed the brake.

See also: hydraulic brake, brake bleed, internal cable routing

Replacing the fluid in a hydraulic brake and getting the air bubbles out. You need to do it if the lever feels spongy or pulls to the bar, and many manufacturers recommend doing it once a year.

See also: hydraulic brake, mineral oil, DOT brake fluid, bite point

The brake fluid used by Shimano, Magura and Tektro, among others. It isn't corrosive and doesn't absorb water. Never mix it with DOT fluid: each brake takes only its own.

See also: DOT brake fluid, brake bleed

Synthetic brake fluid (DOT 4 or 5.1) used by SRAM, Hayes and Formula, among other brands. It has a higher boiling point than mineral oil, but it absorbs moisture over time and damages paint.

See also: mineral oil, brake bleed

Ways of attaching the caliper to the frame and fork. Flat Mount is the road and gravel standard; Post Mount is the mountain bike standard; the old IS mount needs an adapter for current calipers.

See also: brake caliper, caliper adapter

A spacer that moves the caliper away from the frame or fork so you can run a larger rotor. With a +20 mm adapter, for example, you go from a 160 mm rotor to a 180 mm one.

See also: brake rotor, Flat Mount / Post Mount

The two ways to attach a rotor to the hub: Shimano's Center Lock, with splines and a lockring tightened with the same tool as the cassette, or 6-bolt (ISO standard). Adapters from 6-bolt to Center Lock exist.

See also: brake rotor, hub

Breaking in new pads or rotors with a series of firm stops (about 20, from 15 to 3 mph, or 25 to 5 km/h, without locking the wheel). It lays down an even layer of pad material on the rotor and the brake gains a lot of power.

See also: brake pads, brake rotor, glazed pads

Pads that have overheated and have a hard, shiny surface: they brake less and squeal. Sometimes you can save them by sanding; if they're contaminated with oil, they have to be replaced.

See also: brake pads, brake fade, bedding-in

A temporary loss of braking power caused by too much heat on long descents. Prevent it with bigger rotors, metallic pads and braking hard in bursts instead of dragging the brakes.

See also: brake rotor, sintered (metallic) pads, glazed pads

A brake inside the rear hub that works when you pedal backward. It's common on kids' bikes, beach cruisers and Dutch city bikes; it stops working if the chain comes off.

See also: hub Kids' Bike Size

A rim brake with long arms mounted on frame bosses, typical of older mountain bikes, city bikes and kids' bikes. It's powerful, but needs levers with V-brake cable pull.

See also: rim brake, brake pads (rim)

A road rim brake with two arms that close on the rim from a single central bolt. On most frames it limits tire width to about 25-28 mm.

See also: rim brake, brake pads (rim)

The ability to control braking anywhere between light and hard without the wheel suddenly locking up. A brake with good modulation delivers its power progressively through the lever stroke.

See also: bite point, organic (resin) pads

The point in the lever stroke where the pads start to bite. Some brakes let you adjust it; if it changes on its own or the lever pulls to the bar, there's usually air in the system or the pads are worn.

See also: reach adjustment, brake bleed, modulation

A screw or dial that moves the lever closer to or farther from the handlebar. If you have small hands, the first knuckle of your index finger should reach the end of the lever without stretching.

See also: brake lever, bite point

The distance the bike travels from when you start braking until it stops. It grows with the square of speed: at 25 mph (40 km/h) you need about four times as much as at 12.5 mph (20 km/h).

See also: modulation, disc brake