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Disc brakes aren’t new, they’ve been used on mountain bikes for years but have recently found popularity on road and triathlon bikes. They use a round metal disc called a rotor attached to the hub of the wheel and a mechanism called a caliper, bolted to the frame or fork. When the rider squeezes the brake lever, the caliper pinches the spinning rotor, creating friction to slow the bike down.
There are three types of disc brakes currently used on bikes: hydraulic actuated, cable actuated, and hybrid cable-hydraulic. Cable actuated options use a metal cable and cable housing; when the brake lever is pulled it creates tension in the cable which squeezes the caliper against the brake disc, much like a standard caliper brake. Hydraulic-actuated brakes use brake oil and a brake hose; when the brake lever is squeezed, the oil is pressurized, forcing pistons inside the brake caliper to squeeze the brake disc. Hybrid disc brakes use both cables and hydraulic oil—although these are uncommon.
Effective and aero: Disc brakes are rapidly gaining popularity on road and triathlon bikes.
Disc brakes may sound more complicated than rim brakes, but they are easier to install and maintain than some of the exotic rim brake designs common on today’s aero bikes, plus they have a few added benefuts. Bikes equipped with them give the rider much better control of their braking, whether the brakes are hydraulic or cable actuated. They also barely lose any stopping power in wet conditions (although slick roads can still cause a wheel to lock up), and they allow for easier wheel changes than rim brake bikes, since there’s no need to adjust the brakes for different wheel widths or change brake pads for different braking surfaces.
Many armchair aerodynamicists were originally critical of the incorporation of disc brakes on bikes whose primary goal is to be aerodynamically efficient. To their credit, it is hard to believe that a chunky disc brake caliper could somehow avoid an aerodynamic penalty. Independent wind tunnel testing, however, has proven that an aero bike with disc brakes can be just as fast, if not faster, than a bike designed around rim brake bikes. According to Nathan Barry, an engineer with Cannondale who has a PhD in applied aerodynamics, “disc brakes remove many of the constraints on the frame, especially at the head tube and fork crown area. Given the importance of this part of the bike, this can be significant overall for aerodynamic performance.
There is also greater flexibility on rim width and shape with disc-brake compatible wheels, which can help significantly in working with contemporary larger tires.”
If you are not one to give your bike all the TLC it really deserves, then rejoice, disc brakes are almost worry-free once correctly installed. Gone are the days of brakes going out of alignment if your bike gets bumped or falls over—no more dreaded brake rub. The only real drawback that you may encounter when using them is that removing and reinstalling the rear wheel is slightly more tricky since you need to align the chain as well as the brake rotor when putting the wheel back in.
Also, disc brake bikes typically use a “thru-axle” instead of a quick release skewer to hold the wheels in place. While thru-axles do not require much as far as learning goes—if you can install a screw, you can install a thru-axle, but they do often require an allen key to remove.
Disc brake bikes do require a little bit of learning, but if you enjoy going faster, having less issues with your bike, and stopping in a more predictable fashion, then there is a very good chance that your next bike will have them.