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Drivetrain

Pedal Power: How Far and How Fast Can You Go?

Your Speed Depends on Overcoming Forces

PEDAL POWER is a combination of how hard and how fast a cyclist pushes on the pedals to overcome all the forces resisting forward motion.

The rate at which work is done or energy is transferred is power. When riding a bike, your PEDAL POWER is the combination of how hard and how fast you push on the pedals to overcome the forces holding you back.

Forces opposing forward motion:

  • Wind Resistance
  • Gravity (Slope Resistance)
  • Rolling Resistance
  • Component Friction
  • Inertia
Wind resistance and inertia slows you down, gravity weighs you down and you compete with rolling resistance and friction 

Power Output 

To determine the power produced by a bicycle, use the equation:

p o w e r = w o r k t i m e
Since work is equal to force times distance

power = force × distance time

Velocity is equal to the bikes distance traveled over time, thus,

power = force × velocity

Cadence

Is the number of pedal revolutions per minute. Like force, cadence impacts the amount of power a cyclist produces.

Power ∝ force,cadence  

To generate more power, a cyclist either needs to push harder(increased force) or pedal faster (increase cadence). The higher your power output, the faster and further you will go!

Mechanical Power  Electrical Power

Mechanical power is generated when you pedal a bike. It can be transferred to electrical power to illuminate a light bulb.

Bike Generator Diagram 

Gears: Changing the Gear Ratio can Determine how far and how Fast you Move

Gear Up!

The gears of a bicycle create mechanical advantage that allows you to easily pedal up steep hills and increase speed going down hills.  Gears are the toothed wheels near the pedals and rear wheel that help you cycle at a comfortable speed with minimal force no matter how steep the terrain. 

The components that are responsible for movement are called the drivetrain. The drivetrain on a bike consists of the pedals, front chainrings, rear cassette, front and rear derailleurs, and the chain.   

Drivetrain diagram

What is a Gear Ratio?

A gear ratio is the number of teeth on the front gear (chainring) divided by the number of teeth on the rear gear (cassette). The gear ratio indicates the number of times the rear wheel will turn for each single revolution of the pedals.

Gear Ratio = 39/14 = 2.79 For each complete turn of the chainring gear, the smaller cassette gear will turn 2.79 times

The combination of the chainring and cassette gear being used will determine if you are in a low gear or a high gear.

Low gear: small chainring gear and larger gears on the cassette. Low gears are those located closest to the bike’s frame.

High gear: large chainring gear and smaller gears on the cassette. High gears are those located furthest from the bike’s frame.

There is no all-encompassing gear ratio in which to ride, rather the appropriate gear ratio depends on the cyclist’s goal (whether to ride leisurely, to train, or to race), the terrain, and other environmental conditions. In the case of pedaling uphill, a cyclist often shifts to a low gear rat io which reduces the amount of force that must be applied to the pedals thereby allowing the cyclist to pedal more easily. However when pedaling on flat surfaces or downhill, cyclists typically shift to a high gear ratio to attain more speed.  

Gear diagram for hill climbing


Gear diagram for speed

Cross Chaining VS Correct Chaining

Cross chaining is the improper location of the chain in relation to the chainrings and cassette gears. It occurs when the largest chainring is used with the larger cassette gears or when the smallest chainring is used with the smaller cassette gears. To reduce chain wear and prevent slipping gears, cross chaining should be avoided at all times. Correct chaining is when the chainring and cassette gears are used in the proper combinations; the large chainring with the smaller cassette gears or the small chainring with the larger cassette gears.

Cross chain diagram