Exercise bicycles let you enjoy the cardiovascular benefits of cycling while staying inside, warm and dry. Through technology, they can even help you plan and pace your workout, down to knowing how fast you're going and how far.
Cycle Components
A stationary bicycle has many components, with different models having different arrangements of parts. However, the components relevant to calculating your speed are consistent from model to model and brand to brand. These components include the pedal wheel, a flywheel and the computer in your display console.
Rotation
The key to a stationary bike's ability to measure your speed comes from the basic physics of rotation. When a wheel spins, the material at any point on that wheel moves a fixed distance for every rotation. An object on the edge of the wheel will move a distance exactly equal to the diameter of the wheel. This distance remains constant no matter how fast the wheel is spinning.
Mechanism
A flywheel -- or laser sensor on more advanced models -- counts the number of rotations the pedal wheel makes throughout your workout. It communicates this information to the computer in your stationary bicycle's console. That computer then compares the information from the sensor to the information from its internal timer. It runs the math and displays your speed based on the number of rotations compared the the time that has passed.
Example
Take, for example, a cycle with a pedal wheel exactly 1 foot in diameter. Each time it rotates one full circle, the sensor in the cycle counts that you have traveled one foot. It communicates that information to the computer in the console. The computer is programmed to count cycles at regular intervals, specifically how long those intervals are varies from model to model. The computer in this example counts and compares every five seconds. If it found you cycled 50 feet in five seconds, it would then computer your speed as just under 7mph.
References
- Ben Cohn; Fitness Coach; Hillsboro, Oregon
- "The New Way Things Work"; David MacCaulay et al; 1999
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