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Drum and Disc Brakes

Drum and disc brakes are less common braking systems for bicycles. Drum brakes work by applying friction from a pad inside an enclosed drum. The drum is part of the hub of a wheel. These type of brakes generate a great deal of heat and warning labels appear on the outside of the hubs warning the rider not to touch the hub for a time after the brakes have been applied. Disc brakes work very much like caliper brakes, with a separate disc attached to the hub. The main benefit is that the disc is away from the wheel spray and consequently any liquid, dirt or other materials. Both of these types of braking systems add more weight to the bicycle, but drum brakes are especially heavy. These types do appear on professional downhill bikes where the added weight is not a concern and the added braking power is essential.


Missy Giove


Missy "the Missle" Giove

Missy "the Missle" Giove is known as one of the top women downhill mountain bike racers in the world. Her sometimes multi-colored dreadlock hairstyle, body piercings, tattoos, and a dead piranha good luck charm (which shes wears around her neck) outwardly demonstrate her extreme attitude--one that has kept her on top of the downhill world.

Downhill riders like Missy generally ride heavier dual-suspension bikes. Since the journey is downhill only, weight is not as much of a consideration. Downhill cycles have heavy-duty brakes--usually the heavier but more effective disc brakes are used.

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Balancing and Steering

After the training wheels come off, riding a bicycle seems as natural as walking to most people. It's easy to take for granted the fact that this type of locomotion involves a complicated system of dynamics, one that is still argued over by scientists today. We know that the mechanism of human power through pedaling is responsible for getting motion started on a bicycle. But how does a bicycle go forward? Why does it stay upright?

Center of Gravity

Most of us remember our own first experiences attempting to balance ourselves on our first set of wheels. Balance is an integral part of our initial training. It's also an important aspect of riding technique at the professional level.

When a rider gets on a bike, her center of gravity shifts upwards as she and her weight are elevated and added to the weight of the bicycle itself. The bicycle with a rider on it is top-heavy and is an unstable object when stationary.

Libor on a ledge
Libor Kiras, expert "Trials" cyclist, rides on the ledge of a tall buidling for a television commercial. Balance in this case is a matter of life or death. There's more on Libor on the next page.

Gyroscopic Action

The geometry of the wheels and the speed at which they travel are also fundamentally important to balance. This is where the term "gyroscopic action" applies; it relates the circular motion of the wheels. Some scientists believe that the gyroscopic action is primarily responsible for keeping the bicycle stable. For instance, a moving wheel is more stable when it is spinning faster. The relative importance of the forces at work changes with the speed at which the wheel spins. A faster spinning wheel experiences lateral forces (like crosswinds) to a greater degree, so forward motion is affected more.

The steering characteristics depend on the speed of the bicycle, as well as the geometrical relationships of its frame and wheels. While at lower speeds the steering angle of the front tire can be quite large, at higher speeds, above 10 miles per hour for example, an angle of only a few degrees is sufficient to topple the bike and its rider.

Interestingly, many scientists are in complete disagreement about even the fundamentals of balancing and steering. Some say that a high center of gravity is beneficial to stability while others advocate a low center of gravity. Some insist that gyroscopic action is responsible for stability, others say the exact opposite.

DistURBing News

A series of experiments by British scientist David Jones centers on the crux of the disagreement among the experts. Jones pioneered project URB, a study in which he tried to construct an unridable bicycle. He intended to cancel out the gyroscopic action of the front wheel of a bicycle by mounting a wheel next to it that rotated in the opposite direction. Jones's findings were that canceling out the gyroscopic action did not affect the ability to steer the bicycle and that the overall stability of the bike wasn't affected. In another experiment, this time using a bicycle without a rider, Jones found that gyroscopic action did make the bicycle more stable. This indicates that the center of gravity (which changes with the addition or subtraction of a rider) may play a significant role in stability. Project URB was a powerful demonstration because it seemingly dispelled a popular conception that the gyroscopic effect of the wheels results in stable motion.


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