Post by Admin on Nov 15, 2014 23:46:14 GMT
Hydraulic Disc Brakes
PART ONE
These days most mountain bikers know what they want in a hydraulic brake--consistent modulation, loads of power and solid durability, to name a few features. But how many actually know how their brakes work?
Squeeze
Squeezing the lever of a hydraulic brake actuates a piston inside the master cylinder (that mass of metal between the lever and handlebar). The piston moves brake fluid toward the brake caliper (that neat little box perched above the disc itself) and the fluid builds pressure within the brake system. The brake fluid pushes against the backs of a set of pistons inside the caliper, moving them toward the rotor. Friction--the basis of stopping--is created. (Physics lesson: A larger rotor correlates to improved leverage and thus more braking power.)
Modulate
"The key to modulation is controllable power, not an on-off feel," says Hayes production manager Rich Travis. "For every millimeter of movement at the lever, we want increased clamp force at the caliper. You want a lever that will engage gradually, yet will still give you kick-ass ending power for emergency situations." Heat, the byproduct of friction at the brake pads and rotor, represents the nemesis of hydraulic brake performance. As the brake fluid warms, it expands, creating unwanted pressure in the brake system. A phenomenon known as lever pump occurs when the over-pressurized brake fluid pushes back against the piston in the master cylinder.
When the lever is released, the spring-loaded piston in the master cylinder slides back past openings called port-timing holes (not shown). These allow excess brake fluid to flow into a reservoir adjacent to the master cylinder. An elastic membrane within the reservoir, the bladder, expands as excess fluid enters the reservoir and contracts as it cools, maintaining consistent pressure within the brake system. At the caliper, the pistons are held in place by a seal that flexes as the brakes are engaged and aids in retracting them from the rotor when the brakes are released. While Travis says the new Stroker utilizes Hayes's best-ever bladder and reservoir technology, to cope with heat, all disc brake systems require a rider to fully release the lever to prevent pump. "On long downhill runs, the rider should get on and off the brakes as much as possible," says Travis.
Burnishing
Lightly stopping 10 to 30 times before riding new or recently cleaned rotors allows the braking compound from the pads to seat onto the rotor surface.
Bleeding
Changing fluid removes gas--formed when the brake fluid gets so hot it boils--plus metal and rubber particles that break down and seep into the system.
Howl
According to Travis, the occurrence of brake howl depends on a number of factors including the stiffness of the frame and brake mounts as well as the kind of brakes and conditions during use. "Some bike and brake combinations just make noise," he says.
Hydraulic discs feature a closed system of hoses and reservoirs containing special hydraulic fluid to operate the brakes. When the lever is activated, a plunger pushes the fluid through the hoses and into the caliper where the pads are pushed onto the rotor, stopping the bike.
The advantage of hydraulic systems is being sealed (or "closed") so that water, dirt or debris can't compromise the brakes, making them very maintenance free once they've been properly installed. Also, hydraulic brakes have a silky smooth feel at the lever and incredible gripping power at the business end.
For drawbacks, hydraulic brakes must withstand extremely high pressure, so expert set-up and frequent inspections are essential. The smallest air bubble or leak in hydraulic discs can cause a loss of power or complete failure. And, the process of removing air from the braking system, called "bleeding," varies between individual systems and can be a delicate process.
PART ONE
These days most mountain bikers know what they want in a hydraulic brake--consistent modulation, loads of power and solid durability, to name a few features. But how many actually know how their brakes work?
Squeeze
Squeezing the lever of a hydraulic brake actuates a piston inside the master cylinder (that mass of metal between the lever and handlebar). The piston moves brake fluid toward the brake caliper (that neat little box perched above the disc itself) and the fluid builds pressure within the brake system. The brake fluid pushes against the backs of a set of pistons inside the caliper, moving them toward the rotor. Friction--the basis of stopping--is created. (Physics lesson: A larger rotor correlates to improved leverage and thus more braking power.)
Modulate
"The key to modulation is controllable power, not an on-off feel," says Hayes production manager Rich Travis. "For every millimeter of movement at the lever, we want increased clamp force at the caliper. You want a lever that will engage gradually, yet will still give you kick-ass ending power for emergency situations." Heat, the byproduct of friction at the brake pads and rotor, represents the nemesis of hydraulic brake performance. As the brake fluid warms, it expands, creating unwanted pressure in the brake system. A phenomenon known as lever pump occurs when the over-pressurized brake fluid pushes back against the piston in the master cylinder.
When the lever is released, the spring-loaded piston in the master cylinder slides back past openings called port-timing holes (not shown). These allow excess brake fluid to flow into a reservoir adjacent to the master cylinder. An elastic membrane within the reservoir, the bladder, expands as excess fluid enters the reservoir and contracts as it cools, maintaining consistent pressure within the brake system. At the caliper, the pistons are held in place by a seal that flexes as the brakes are engaged and aids in retracting them from the rotor when the brakes are released. While Travis says the new Stroker utilizes Hayes's best-ever bladder and reservoir technology, to cope with heat, all disc brake systems require a rider to fully release the lever to prevent pump. "On long downhill runs, the rider should get on and off the brakes as much as possible," says Travis.
Burnishing
Lightly stopping 10 to 30 times before riding new or recently cleaned rotors allows the braking compound from the pads to seat onto the rotor surface.
Bleeding
Changing fluid removes gas--formed when the brake fluid gets so hot it boils--plus metal and rubber particles that break down and seep into the system.
Howl
According to Travis, the occurrence of brake howl depends on a number of factors including the stiffness of the frame and brake mounts as well as the kind of brakes and conditions during use. "Some bike and brake combinations just make noise," he says.
Hydraulic discs feature a closed system of hoses and reservoirs containing special hydraulic fluid to operate the brakes. When the lever is activated, a plunger pushes the fluid through the hoses and into the caliper where the pads are pushed onto the rotor, stopping the bike.
The advantage of hydraulic systems is being sealed (or "closed") so that water, dirt or debris can't compromise the brakes, making them very maintenance free once they've been properly installed. Also, hydraulic brakes have a silky smooth feel at the lever and incredible gripping power at the business end.
For drawbacks, hydraulic brakes must withstand extremely high pressure, so expert set-up and frequent inspections are essential. The smallest air bubble or leak in hydraulic discs can cause a loss of power or complete failure. And, the process of removing air from the braking system, called "bleeding," varies between individual systems and can be a delicate process.
