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Cars have been outfitted with them for years, so have motorcycles.
But hydraulic brakes are still relatively young technology in the realm
of mountain biking. The ever-popular v-brake (manual bar mounted
lever pulls on cable to activate pads that squeeze outside of wheel) was
first replaced by the manual disc brake (which also used a cable
activated system to squeeze 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 much more weight than
their manual counterparts.
Lets take a look at how a hydraulic brake system actually
works. The brake lever is now connected to a hydraulic line that uses
fluid to transmit the pressure from the lever to the brake pads. 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, which rotates at the
same speed as the wheel. This relationship of the smaller piston using
fluid pressure to activate the larger one, the force is multiplied at
the wheels.
The handle bar levers must now contain a master cylinder- a
small canister that insures that there is enough fluid in the reservoir
that if the pads thickness changes (due to wear), or the fluid expands
or contracts (due to being heated or cooled), there will still be enough
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).
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