Road disc brake calipers

How to choose a road bike disc brake caliper

The caliper clamps the pads onto the rotor. On a bike with hydraulic road brakes, it forms a closed system with the lever: the two must be chosen together, and the master cylinder is housed in the lever. A caliper on its own is replaced after a crash or a leak, not to change how the braking feels.

Flat Mount or Post Mount

• Flat Mount : the road bike standard, used on all recent disc brake frames. The caliper bolts flush to the frame or fork, making for a more compact setup.
• Post Mount : inherited from mountain bikes, still found on some older setups and on SRAM BB5 and BB7 mechanical calipers.
• An adapter lets you switch between Post Mount and Flat Mount, or fit a larger rotor to a given mount.

The mounting bolt is not a minor detail

Shimano offers its Flat Mount bolts in types A, B, C and C2 : their length depends on the thickness of the frame or fork at the mounting point and whether an adapter is fitted. A bolt that is too short will not engage enough threads; one that is too long will bottom out before it can be tightened. They are sold separately and are easy to overlook when changing a caliper or rotor size.

Hydraulic or mechanical

• Hydraulic : almost the entire range. The caliper comes pre-bled as part of a complete brake set, but needs bleeding if fitted on its own.
• Mechanical (SRAM BB5, BB7 Road) : the caliper is cable-operated and controlled by a conventional lever. An option for adding disc brakes to a bike with mechanical levers, often sold with a rotor.
• A mechanical caliper cannot be used with a hydraulic lever, and vice versa.

Front and rear are not identical

Front and rear models are generally different: the hose connection angle and bleed screw position vary. Some brands offer a caliper that can be used at either end; this will be stated in the product title.

To find out more: How to adjust your road bike brakes

See also: Road brake rotors · Road brake pads · Road bike disc brake adapters