Build a road bike, or take a folding bike seriously, and brakes are the last problem left. Frame, wheels, drivetrain can be swapped one at a time. Real hydraulic braking used to mean new shifter-levers, a full re-route, bleeding, and starting over on the feel you already know.

The GTF-4 removes that choice. Cable in, hydraulic out. Your cable and levers stay; a complete sealed hydraulic system works inside the caliper. Flat Mount is the standard on modern road and gravel frames and on more and more new folding bikes, and the GTF-4 fits it directly.

Four pistons spread the push evenly across the pad, so the contact patch is fully loaded. Braking does not arrive in a lump; it grows in a line with your finger. As much as you ask for, and no more. That is what modulation means. Pads wear evenly, so maintenance stays predictable.

Next to the six-piston GTF-6, the GTF-4 trades two pistons for a lighter body, wider frame compatibility and a simpler install. It is not a cut-down GTF-6. It is 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. Then multi-axis CNC cuts the piston bores, the oil passages and every mating surface. Forging gives strength; machining gives precision. 136 g per caliper is what that process yields, not what thinning the structure would.

The Flat Mount envelope leaves far less room than Post Mount. Fitting four pistons, full oil passages and the adjuster into that space is the real difference between the GTF-4 and the GTP-4: not a spec choice, a structural one.

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.