Anyone upgrading brakes hits the same wall. Real hydraulic performance means new shifter-levers, a full re-route, bleeding, and a bill that often exceeds the caliper itself. Or keep the cables and live with the soft, hesitant, heat-fading feel of an ordinary cable system.

The GTP-4 exists to refuse that question. Cable in, hydraulic out. It is the point in more than a decade of JuinTECH cable-hydraulic work where performance and ease of installation meet most cleanly, which is why builders of high-end metal road frames specify it straight from the factory.

Four pistons in opposed pairs load the pad evenly across its face. Braking does not arrive in a lump; it grows in a line with your finger. As much as you ask for, and no more. Pads wear evenly and maintenance stays predictable.

Next to the six-piston GTP-6, the GTP-4 trades two pistons for a cleaner body, wider frame compatibility and a simpler install. Not a cut-down GTP-6. The right answer to a different ride.

The body starts as a European high-purity 6061 aluminium billet, die-forged so strength and grain structure are pressed into the metal. Multi-axis CNC then cuts the oil passages, piston bores and every mating surface. Forging gives strength; machining gives precision. 133 g per caliper follows from the process, not from thinning the structure.

The body is anodised, never painted, because paint would trap the heat the pistons are working to move out.

Your legs put the energy in. Braking does not make it disappear, it converts it. Every bit of speed you shed becomes heat, and two parts you could hold in one hand have to absorb all of it.

Most calipers use phenolic pistons to keep that heat away from the body. The heat has nowhere to go, so it builds in the pad until the surface glazes and the brake fades. Our pistons are 7075 aluminium with a wear-resistant coating: they pull heat away from the pad and into the body, so the whole caliper becomes a cooling surface. The rotor does its own share through surface area and airflow. Two parallel paths, no hand-off.

A cable-actuated hydraulic caliper takes the force from your hand through the brake cable and multiplies it hydraulically inside the body. Between lever and caliper, the cable is the single most important part of the chain.

Run compressionless outer housing and a low-friction inner cable. Ordinary housing compresses under load and eats part of your pull; a rough inner cable blurs the feedback and slows the return. These two are not optional extras. They are what lets the caliper deliver everything it has.