Gravel brake callipers

How to choose your gravel brake calliper

A calliper can be replaced after an impact, when a piston seizes, or to gain braking power without changing the whole system. Three factors determine compatibility, and the first is the frame.

Flat Mount or Post Mount

• Flat Mount : the standard on recent gravel and road frames. The calliper bolts on flat, close to the frame. Bolts come in different lengths depending on the frame thickness and whether an adapter is used — they are not supplied with every calliper.
• Post Mount : inherited from mountain bikes, still found on older gravel frames and some suspension forks. The calliper mounts on two perpendicular tabs.
• Switching from one to the other isn’t straightforward: Flat Mount to Post Mount adapters exist, but the reverse isn’t always possible.

Front or rear

Front and rear aren’t interchangeable. A front calliper has a different body and hose connection angle from a rear one. Shimano GRX product listings make this explicit; with Hope, the designation FMF indicates the front version. Buy the calliper for the wheel in question.

Hydraulic or mechanical

• Thehydraulic is the standard: more power, less effort at the lever and automatic adjustment as the pads wear.
• The cable-actuated mechanical braking (SRAM BB5, Avid BB7, Shimano RS305) still has a real advantage for gravel touring: you can repair it anywhere with a cable and an Allen key, without bleeding or fluid.
• A hydraulic calliper cannot be operated by a cable-actuated lever, or vice versa.

Brake fluid — the detail you can’t overlook

Shimano and Campagnolo usemineral oil, while SRAM uses DOT. These two fluids are incompatible: mixing them destroys the calliper seals. Pay particular attention to this with Hope, available in a DOT or mineral oil for the same model — the lever already fitted to the bike determines which version you need.

The number of pistons

Standard gravel callipers have 2 pistons. The 4-piston Hope RX4+ callipers were designed to replace a road or gravel calliper while retaining the original lever: more power and better braking on long descents, for a loaded bike or mountain riding. The designation (+20) indicates the version intended for a 160 mm rotor rather than a 140 mm one.

What’s not included

Most callipers are sold without a rotor, and often without a hose or pads. Check what’s in the box before ordering: a calliper on its own means reusing your hose, so you’ll need to bleed the system.

To find out more: How to adjust your bike brakes

See also: Gravel brake pads · Complete gravel brakes · Road brake rotors