1x Drivetrains

Summary

A 1x drivetrain is a bicycle gearing system that uses a single front chainring paired with a wide-range rear cassette. By eliminating the front derailleur and consolidating all shifting at the rear, it simplifies operation, reduces weight, and improves reliability — especially in rough or technical terrain. Originally designed for mountain biking, the 1x format has become dominant off-road and is increasingly popular in gravel and selective road applications.

Key Facts

  • Introduced: Late 2000s (mainstream adoption from ~2012)
  • Category: Concept
  • Also Known As: One-by drivetrain, single-ring drivetrain
  • Used By / Found On: Mountain bikes, gravel bikes, cyclocross, e-bikes, select road bikes
  • Typical Gearing: 10–50T or wider rear cassettes
  • Replaces: Traditional 2x (double) or 3x (triple) front chainring systems
  • Modern Status: Standard in MTB and gravel; growing niche in road, common in e-bikes

Overview

A 1x drivetrain—pronounced “one-by”—uses one front chainring combined with a large-range cassette at the rear to cover a wide spectrum of gearing. This streamlined approach eliminates the front derailleur and its associated shifter and cabling, reducing system complexity and making gear changes more intuitive.

First popularized in mountain biking, the format gained momentum with SRAM’s XX1 11-speed system in 2012, which introduced a purpose-built wide-range cassette and a narrow-wide chainring to maintain chain security. The design eliminated one of mountain biking’s persistent issues—chain drops—and simultaneously simplified operation in unpredictable terrain.

As cassettes grew to 12 and even 13 speeds, the 1x format began to match or even exceed the gear range of traditional 2x systems, making it viable for gravel, cyclocross, and some road disciplines. Riders appreciate the focused control, reduced weight, and lower mechanical failure potential — particularly in demanding off-road or endurance environments.

How It Works

A 1x drivetrain focuses entirely on the rear of the bike for gear management, using specialized components to ensure chain retention, range, and durability.

1. Chainring Design

The cornerstone of a modern 1x drivetrain is the narrow-wide chainring. These rings alternate narrow and wide teeth to mirror the spacing of inner and outer chain links, creating a positive mechanical engagement that keeps the chain locked in place — even on bumpy trails.

This innovation reduces or eliminates the need for chain guides and compensates for the absence of a front derailleur, which previously played a role in keeping the chain aligned.

2. Wide-Range Cassette

1x systems use oversized rear cassettes to deliver the gear range previously split across multiple front rings. Common sizes include:

  • 10–42T (11-speed MTB)
  • 10–50T (12-speed Eagle)
  • 10–52T (SRAM Eagle update)
  • 9–46T (e.g., e*thirteen TRS+)
  • 10–44T or 10–45T (gravel 1x systems)

These cassettes cover both climbing and high-speed needs, though the jumps between gears are generally larger than in 2x systems.

3. Rear Derailleur & Clutch Mechanism

To manage these wide gear ranges and prevent chain slap, 1x derailleurs use clutch mechanisms that add tension to the derailleur cage. This keeps the chain taut, reduces bounce on rough terrain, and enhances chain retention.

Other design features include:

  • Extended cage lengths
  • Larger lower jockey wheels
  • Optimized cable routing or electronic shifting modules

Together, these enable smooth, stable shifting across wide cassette spreads.

4. Single-Shifter Simplicity

With no front derailleur, the rider controls all shifting through one shifter — usually the right-hand lever. This simplification reduces cockpit clutter and cognitive load, particularly beneficial during technical descents, off-road sprints, or high-focus racing situations.

Some 1x systems also incorporate wireless or electronic shifting (e.g., SRAM AXS), further cleaning up the handlebar setup and eliminating cables entirely.

Advantages & Tradeoffs

Benefits

  • Mechanical Simplicity: No front derailleur, cable routing, or shifter
  • Weight Savings: Fewer components reduce overall bike weight
  • Improved Chain Retention: Narrow-wide rings + clutch derailleurs = secure drivetrain
  • Reduced Maintenance: Fewer moving parts mean fewer adjustments and lower failure risk
  • Cleaner Aesthetics: Sleeker drivetrain layout with fewer cables and components
  • Ideal for Technical Terrain: Single-lever control lets riders focus on handling and timing

Tradeoffs

  • Wider Gear Steps: Larger jumps between gears can disrupt cadence
  • Limited Gear Range (Compared to 2x): Some setups lack ultra-low climbing or ultra-high sprint gears
  • Higher Chain Wear: Chain runs at more extreme angles in certain gears
  • Cassette Weight: Wide-range cassettes are often heavier than compact road cassettes
  • Less Efficient for Road Use: 1x gearing may not match the cadence precision needed for road racing or fast group rides

To address these issues, manufacturers have added more speeds (12 and 13), refined derailleur capacity, and introduced cassette profiles with smaller tooth jumps near the high end.

Use Cases & Market Position

  • Mountain Biking:
    • Status: Universal. From XC to downhill, nearly all new MTB drivetrains are 1x.
    • Why: Simplicity, chain security, and terrain-adapted gearing.
  • Gravel & Cyclocross:
    • Status: Widely used, often competing with 2x.
    • Why: Low maintenance, cleaner cockpit, fewer moving parts in dirty conditions.
  • Road Cycling:
    • Status: Niche but growing. Seen in TT, triathlon, and minimalist endurance builds.
    • Why: Aerodynamics, simplicity, and lighter weight — but gear steps remain a limitation.
  • E-Bikes:
    • Status: Common, especially with mid-drive motors.
    • Why: Motor torque fills in for gear range; simplified drivetrains improve durability.
  • Commuting / Bikepacking:
    • Status: Increasingly common on adventure, hybrid, and trekking bikes.
    • Why: Low fuss, easy operation, and less to go wrong in remote areas.

Notable Implementations

  • SRAM Eagle (XX1, X01, GX, NX, SX):
    • The first 12-speed MTB groupset with 500% gear range — benchmark for modern trail and enduro setups.
  • Shimano Deore XT / SLX 12-speed:
    • Durable, precise MTB systems with Shadow+ clutch derailleur and wide 10–51T cassette.
  • SRAM Force / Rival AXS 1x (Road & Gravel):
    • Wireless 1x drivetrains with electronic shifting and X-Range gearing logic.
  • Campagnolo Ekar 1×13:
    • First 13-speed gravel-specific groupset with a 9–42T cassette and tight mid-range spacing.
  • Specialized Diverge STR (1x builds):
    • High-end gravel bike that blends road speed and off-road capability using a wide-range 1x system.
  • Yeti SB150 / SB160:
    • Long-travel enduro bikes built exclusively around 1x systems, optimized for chain security and big descents.

Related Terms

  • Narrow-Wide Chainring
  • Wide-Range Cassette
  • Clutch Derailleur
  • Eagle Drivetrain
  • 12-Speed
  • Front Derailleur (legacy)

See Also on BBB

References

  • SRAM Technical Docs: Eagle Drivetrain Architecture
  • Shimano Product Guides: Deore XT M8100 1x Systems
  • Campagnolo Ekar 13-Speed White Paper
  • Pinkbike: “The Rise of 1x Drivetrains”
  • BikeRadar: “Why 1x is Taking Over”
  • Cyclingtips: 1x vs 2x Gear Range Charts & Analysis
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