Mountain bike gears work by changing the mechanical advantage between the pedals and the rear wheel, allowing riders to maintain an efficient pedaling speed (cadence) across varying terrain.
Mountain bike gears allow you to manage the resistance you feel when pedaling. When climbing a steep hill, you need an "easy" gear to reduce the effort per pedal stroke, even though you'll move slower. On flat ground or downhill, you can use a "hard" gear to go faster with each pedal stroke, requiring more effort.
Key Components of a Mountain Bike Gear System
A typical geared mountain bike uses a derailleur system involving several main parts:
Chainrings (Front Sprockets)
Located by the pedals, attached to the crankset. Older bikes might have 2 or 3 chainrings of different sizes. Many modern mountain bikes use just one chainring at the front, simplifying the system.
Cassette (Rear Sprockets)
Found on the rear wheel hub, the cassette is a cluster of multiple sprockets, or cogs, ranging significantly in size from very small to very large. This is where most of the gear options come from on modern bikes.
Chain
The chain is the link that transfers power from the pedals (via the chainrings) to the rear wheel (via the cassette). The chain follows a specific path through the system. As described in the reference: "The chain runs around the cassette cogs. And then is threaded. Through two cogs on the derailleur itself now these are the upper jockey wheel." The chain also runs around the selected chainring at the front.
Derailleurs (Front and Rear)
These are the mechanical arms that physically move the chain from one sprocket to another.
- The front derailleur (if present) moves the chain between the chainrings.
- The rear derailleur moves the chain between the cassette cogs. It also maintains appropriate chain tension as you shift between different sized cogs. The reference specifically mentions the "two cogs on the derailleur itself now these are the upper jockey wheel," which are the small wheels on the rear derailleur cage that the chain passes through, guiding it and managing slack.
How Gear Shifting Works
When you shift gears using the levers on your handlebars:
- The lever pulls or releases a cable (or sends an electronic signal).
- This action moves the corresponding derailleur sideways.
- The derailleur pushes the chain off its current sprocket onto a neighboring one of a different size.
- This changes the gear ratio, altering how many times the rear wheel spins for each rotation of the pedals.
- Shifting to a larger cog on the cassette (or a smaller chainring at the front) makes pedaling easier (lower gear ratio) – good for climbing.
- Shifting to a smaller cog on the cassette (or a larger chainring at the front) makes pedaling harder (higher gear ratio) – good for speed on flat ground or downhill.
Gear Ratios Explained Simply
A gear ratio compares the number of teeth on the front chainring to the number of teeth on the rear cog. A smaller front ring driving a larger rear cog results in a "low" gear ratio – you pedal more times, but with less effort, to turn the wheel once. A larger front ring driving a smaller rear cog results in a "high" gear ratio – you pedal fewer times, with more effort, to turn the wheel once.
| Gear Combination | Relative Ratio | Pedaling Effort | Speed (at same cadence) | Best For |
|---|---|---|---|---|
| Small Front / Large Rear | Low | Easy | Slow | Climbing Hills |
| Large Front / Small Rear | High | Hard | Fast | Flat/Downhill |
Practical Insights
- Find your rhythm: The goal is often to find a gear that allows you to pedal at a comfortable, consistent speed (cadence).
- Shift preemptively: Anticipate changes in terrain and shift before you hit a steep hill, for example, so you're not trying to shift under heavy pedaling load.
- Smooth is key: Ease up slightly on the pedal pressure while shifting for smoother transitions and less wear on components.
Mountain bike gears, therefore, provide the rider with the flexibility to tackle a wide variety of trails and gradients efficiently by allowing them to select the optimal resistance for pedaling.
