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Braking & Steering
Page: 2 of 3
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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.
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IMAGES COURTESY OF CANNONDALE BICYCLES
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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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Calculate Minimum Stopping Distance of a Bicyclist
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Fill in the information in the boxes.
Velocity
is your velocity as read on a speedometer. Units are
mi/hr.
Click on the "Calculate" button.
Notice the stopping distance and how it increases with speed and how
it changes with different surfaces.
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This calculation requires a JavaScript-capable browser.
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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.
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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.
IMAGE PROVIDED BY CANNONDALE.
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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.
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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.
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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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Braking & Steering
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Exploratorium
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