Brake calipers
Four-piston hydraulic disc brake calipers, Flat Mount for road and gravel, Post Mount for MTB. The mount is read off the frame, the fluid off the levers already fitted.
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The mount: read the frame and fork
Road and gravel use Flat Mount, with the caliper sitting flat on the mount. MTB uses Post Mount, with the caliper bolted onto two posts, like the XCR Pro E4 with its 74.2 mm spacing. The "+20" on the Hope RX4+ SL moves the pads 10 mm further from the hub. On a frame designed for 140 and 160 mm, the RX4+ SL FM+20 takes a 160 mm rotor directly, without an adapter, and a 180 on a 160/180 frame; at the front, the RX4+ SL FMF+20 does the same on the fork. Those 10 mm of radius act as a lever arm: for the same effort, at least 14% more torque than with a 140.
The fluid follows the levers
The RX4+ SL are calipers only, connected to the hose of your existing levers with the supplied Hope fittings. Their version therefore depends on those levers: DOT for SRAM, mineral oil for Shimano and Campagnolo. A D or an M engraved on the bore cap tells you which one you have in hand, and red O-rings mark the mineral version. The XCR Pro E4 runs on DOT 4 or 5.1; beware the name trap, DOT 5 is a silicone fluid and must never be used.
Four pistons: what changes
Two 14 mm and two 16 mm pistons push the pads, in a one-piece body machined from 2014 T6 aluminium. According to Hope, this stiffness gives a less vague lever feel and pads that drag less. Each RX4+ SL comes with two sets of pads, blue for road, red for gravel and cyclocross.
Fitting
The M5 bolts are not included, because the mount varies from frame to frame. The workshop rule: bolt length equals the thickness it passes through, plus what it needs to engage, 7 to 8 mm into the caliper at the rear, 8 to 9 mm into the fork at the front. The rotor is ordered separately, from our Center Lock brake rotors. Hope guarantees spare parts for at least ten years after the end of production.
Frequently asked questions
Flat Mount or Post Mount caliper?
The one your frame or fork takes: Flat Mount on most disc road and gravel bikes, Post Mount on MTBs. Each caliper's specifications give its mount and spacing.
Can I fit a Hope caliper with Shimano or SRAM levers?
Yes, that is what the RX4+ SL is made for: DOT version for SRAM levers, mineral version for Shimano and Campagnolo. The list of compatible levers is in the specifications.
Why won't a caliper piston retract?
Most often, it is dirty. Remove the pads, clean the pistons, push them back with a plastic lever, then ease them out gently with the brake lever. If a piston stays stuck, the caliper goes to the workshop.