I am trying to mount some Hope calipers to some custom brake levers.

Hope say the calipers - RX4+ - can be used safely with Shimano and Campy levers in their mineral oil form. I want to know if the modified TRP levers I would like to use push a similar amount of fluid to ensure decent modulation. They are mineral oil obviously but if the fluid volume is significantly different they may need more modification in order to work.

It's for a very custom application - hence the lack of interest in using Shimano or Campy - I know this is the hard way to do things.

Does anyone know how many ml of fluid hydro brakes from various manufacturers move?

  • Why not grab any Shimano caliper and check if it works? Commented Sep 8, 2021 at 19:29
  • I know the caliper works and I know a Shimano lever will work. What I need to know is if it will work correctly with my lever. For that I need the fluid volume, I don't just want to guess if possible. If I know what's correct I can ensure it's delivered.
    – Mr73
    Commented Sep 8, 2021 at 23:35
  • I can't help with an answer, but I'm curious about your custom brake levers. Feel free to add some background, perhaps photo, or if its going to detract from this question, then post in Bicycles Chat instead.
    – Criggie
    Commented Sep 9, 2021 at 0:27
  • Its all in the piston area (diameter). If the area is the same, the distance moved for the same volume is the same. If the area is larger, the distance moved is less.
    – mattnz
    Commented Sep 9, 2021 at 1:33
  • Thanks for the input mattnz. I understand the piston stuff - vaguely remembered from my Physics courses. The issue is that I can't change the piston bores in the caliper easily, and that they should be fine given that Hope say they can be used with Shimano, Campy and Sram levers. The unknown is how much fluid the TRP piston moves relative to those other brands.
    – Mr73
    Commented Sep 9, 2021 at 18:00

1 Answer 1


I don't have a fluid displacement number and haven't done this, but there are a lot of mixed reports around the internet of people mixing TRP Hylex levers with Shimano calipers, so I bet it's very close and would be totally fine.

The other piece to worry about is the hose/fitting compatibility. Both the Hylex and the RX4+ want the hose connection they were designed for. The mineral oil RX4+ has its own special fitting and it appears to be all sized to fit a Shimano hose. TRP hoses are a little bigger than Shimano (5.3mm vs 5mm) and Shimano barbs are known to fall out of them when doing this, so it's a good bet the Hope barb would too. Some have reported success getting the TRP barbe and olive to work with Shimano BH90 hose, the question mark there being is it actually secure enough with a little play in inside the olive before it all gets squashed. It probably is, but that's the experiment you'd be doing.

  • 1
    Thanks. You're right on both counts. I'm just trying to eliminate guesswork. As for the hoses I can use an oversized hose on the caliper and let the compression fitting do its thing - .2mm is small enough to be within tolerances I think and properly screwed down should be tight. If that doesn't work I can run the caliper on 5mm, the lever on 5.3 and join them with a hydraulic fitting or, more simply, make a custom barb with the right interior diameter for a 5.3mm hose and the right externals for the caliper.
    – Mr73
    Commented Sep 8, 2021 at 23:41

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