Bicycle gears work by allowing you to change the ratio between how fast you pedal and how fast your wheels turn. This lets you maintain a comfortable pedaling speed (cadence) regardless of terrain or speed.
The Basics of Bicycle Gearing
At its core, a bicycle gearing system involves:
- Chainrings: The sprockets attached to the pedals (crankset).
- Cassette or Freewheel: The cluster of sprockets on the rear wheel.
- Chain: Connects the chainrings to the cassette.
Changing gears essentially moves the chain onto a different-sized sprocket, altering the gear ratio.
Understanding Gear Ratios
A gear ratio is the relationship between the number of teeth on the front chainring and the number of teeth on the rear sprocket the chain is currently on.
- Larger front chainring + Smaller rear sprocket: This combination gives a higher or harder gear. You pedal less often, but each pedal stroke moves the wheel a greater distance. This is good for going fast on flat ground or downhill.
- Smaller front chainring + Larger rear sprocket: This combination gives a lower or easier gear. You pedal more often, but each pedal stroke requires less effort and moves the wheel a shorter distance. This is ideal for climbing hills or starting from a stop.
Think of it like using different gears in a car – lower gears for power, higher gears for speed.
How Derailleur Gears Work
The vast majority of modern bikes use derailleurs to change gears. Derailleurs are mechanical devices that physically move the chain from one sprocket to another.
The Rear Derailleur
Located at the rear wheel, the rear derailleur is responsible for moving the chain across the cogs on the cassette.
- Movement: When you shift gears using your controls (shifters) on the handlebars, the rear derailleur moves the chain up or down the cassette.
- Shifting Mechanism: To facilitate the chain moving onto a different sprocket, when a shift is initiated, the derailleur forces the chain against a machined ramp in the gear. These ramps and tooth profiles on the sprockets help guide the chain smoothly from one size to the next.
- Chain Tension: The rear derailleur also has a sprung cage that takes up slack in the chain, ensuring proper tension as you switch between different sized sprockets.
The Front Derailleur
Found near the pedals, the front derailleur moves the chain between the chainrings. It typically pivots side-to-side, pushing the chain from one chainring to another. Like the rear, the chainrings often have pins and ramps to aid shifting.
The Shifting Process
- Initiate Shift: You actuate a shifter on your handlebars.
- Cable/Electronic Signal: This pulls or releases a cable (or sends an electronic signal) connected to a derailleur.
- Derailleur Moves: The appropriate derailleur (front or rear) pivots or moves laterally.
- Chain Guided: The derailleur cage pushes the chain. At the rear, it forces the chain against a machined ramp in the gear on the cassette to help it lift and move onto the next sprocket. At the front, it pushes the chain onto the next chainring.
- New Gear Ratio: The chain settles on the new sprocket/chainring combination, establishing a new gear ratio and changing your pedaling effort relative to wheel speed.
By understanding this system, you can use your gears effectively to tackle different riding conditions, making your ride more efficient and enjoyable.
