Hydraulic Brakes: New to Bicycles but Old Hat Elsewhere

Cars have been outfitted with them for years, so have cycles and ATVs. But hydraulic brakes are still a relatively young technology in the realm of mountain biking. Before we get ahead of ourselves, let us first take a moment to review how all brakes function to slow a moving object. Brakes convert kinetic energy (motion) into heat energy (friction). This transfer of energy slows the object in motion, and if enough energy transfers, the object actually comes to a stop. Amazingly, the first hydraulic brakes to appear on automobiles dates back to 1918!

The Long Standing V

The ever-popular v-brake (manual bar-mounted lever pulls on a cable which squeezes a caliper so that the pads make contact with the outside of the wheel) was first replaced by the manual disc brake. The manual disc also used a cable-activated system to squeeze a caliper that pushes the brake pads on a rotor. More recently bikes are being outfitted with hydraulic braking systems. Unfortunately, although very effective in fade-free stopping power, these systems are generally more complicated and bring with them a slight weight disadvantage over their manual counterparts.

How It Works

Now lets take a look at how a hydraulic brake system actually works. The brake lever is now connected to a hydraulic line that uses pressurized fluid to transmit the force from the lever to the caliper & hence the brake pads themselves. The lever presses a small piston that applies pressure to the fluid within the line, which begins the chain of events. Down at the wheels, another (larger) piston squeezes the pads onto the disc (or rotor) which rotates at the same speed as the wheel. This relationship of the smaller piston using fluid pressure to activate a larger one is how the force is multiplied at the wheels. In English, this process is felt by requiring less rider pressure at the lever to have instantaneous results at the wheel.

With a hydraulic system, the handle bar levers must now contain a master cylinder- a small canister that insures that there is enough fluid in the reservoir to keep the system pressurized. It is also the master cylinder that acts as a reservoir so that should the pad's thickness changes (due to wear), or fluid expansion or contraction (due to being heated or cooled), there will still be adequate fluid in the system to actuate the brakes. This also contributes to more consistent braking power and feel at the levers, otherwise braking efficiency would fluctuate at the beginning of the ride (as the fluid is still cool) and during (as the fluid heats up from friction).