Summary
Indexed shifting is a gear-changing system that uses pre-defined detents—clicks—in the shifter to correspond with each gear position on the cassette or chainrings. It allows precise, repeatable shifts without needing to “feel” for gear alignment, marking a major turning point in drivetrain usability and performance.
Key Facts
- Introduced: Mid-1980s (mainstream adoption began with Shimano’s SIS in 1984)
- Category: Technology / History
- Also known as: Click shifting, SIS (Shimano Index System), indexed derailleur shifting
- Key benefit: Defined gear positions for accurate, user-friendly shifting
- Used in: Road, mountain, hybrid, touring, and e-bikes
- Found on: Mechanical and electronic drivetrains
- Still used today? Yes — foundational to all modern drivetrains
- Official websites: https://www.shimano.com, https://www.campagnolo.com, https://www.sram.com
Overview
Indexed shifting transformed the bicycle drivetrain from an art of fine-tuning to a system of mechanical precision. Prior to its mainstream adoption in the 1980s, gear shifting was “friction-based”—meaning the rider manually moved the derailleur via a lever with no physical stops or clicks. You had to feel and listen for the gear to settle into place. For many riders, especially beginners or those shifting under pressure, this made gear changes awkward, unreliable, or imprecise.
The advent of indexed shifting introduced pre-set detents (or “indexes”) in the shifter. Now, each click corresponded to a specific gear. Move the lever one step, and the derailleur would align perfectly with the next cog. Suddenly, gear changes became intuitive, consistent, and accessible to a much wider audience.
Shimano was the first to commercialize the concept at scale with the launch of SIS (Shimano Index System) in 1984. While Campagnolo and SunTour had experimented with indexing earlier, Shimano’s holistic integration—matching shifter, derailleur, cable pull, and cog spacing—made the system work reliably. By the late 1980s, indexed shifting was common on both mountain and road bikes, reshaping drivetrain expectations forever.
Today, every major mechanical drivetrain uses indexing in some form, whether it’s a simple 7-speed commuter bike or a race-tuned 12-speed mountain bike. Even electronic systems, like SRAM AXS and Shimano Di2, operate on the same principle—precise, indexed gear positions—albeit digitally controlled.
How It Works
Indexed shifting relies on mechanical detents built into the shifter. Each detent corresponds to a specific amount of cable pull (or push), which moves the derailleur a fixed distance. That movement aligns the derailleur with the next cog or chainring.
Core Components
- Indexed Shifter: Contains a ratcheting or spring-loaded mechanism with fixed stops that click into place. When you shift, the mechanism moves the cable a precise amount per click.
- Derailleur: The mechanism that physically moves the chain from gear to gear. It must be compatible with the indexing system in terms of cable pull ratio.
- Shift Cable and Housing: Transmits force from the shifter to the derailleur. Any stretch or friction here affects shift accuracy.
- Cassette/Chainring Spacing: Must match the indexing system’s assumptions about cog or ring distance. If cog spacing doesn’t match the shifter’s cable pull, shifting will be misaligned.
Mechanical Principles
Each shift “click” moves the derailleur a specific distance determined by the shifter’s cable pull per click and the derailleur’s actuation ratio—the amount the derailleur moves per unit of cable.
- A typical 10-speed road shifter might pull 2.8mm of cable per shift.
- The derailleur actuation ratio converts that pull into a sideward movement of, say, 4mm—matching the cog spacing.
All of these elements must work in harmony. If any component—shifter, derailleur, cassette, or chain—falls out of spec, shifting degrades.
Adjustment & Tuning
- Barrel Adjuster: Fine-tunes cable tension to center the derailleur on each gear.
- Limit Screws: Prevent the derailleur from shifting too far outward or inward.
- B-tension Screw: Affects derailleur body position and chain wrap, especially relevant for wide-range cassettes.
Modern drivetrains often include clutch-equipped derailleurs, optimized tooth profiles (like Shimano’s Hyperglide+), and precise manufacturing tolerances—all of which depend on accurate indexing to function correctly.
Historical Impact & Modern Relevance
The introduction of indexed shifting wasn’t just a mechanical upgrade—it democratized multi-gear bikes. Riders who struggled with friction levers could now change gears confidently and consistently. For racing, it meant faster, more reliable shifts under pressure. For casual riders, it meant less frustration and more usability.
Key Milestones
- 1984: Shimano SIS launches on select road and touring bikes.
- 1987: Indexed mountain bike systems begin to appear (e.g., Shimano Deore XT with thumb shifters).
- 1990s: Integrated shift/brake levers (e.g., Shimano STI) make indexed shifting even more intuitive.
- 2000s: SRAM introduces 1:1 actuation ratio indexed systems, improving shifting under load.
- 2010s–2020s: Electronic indexing emerges (e.g., Shimano Di2, SRAM AXS), offering even more precise shift logic.
Today, friction shifting is mostly reserved for vintage bikes, track setups, or niche endurance events. Indexing is the global standard, used on bikes ranging from Walmart specials to WorldTour machines.
Notable Implementations
- Shimano SIS (1984): First reliable, mainstream indexed shifting system.
- Campagnolo Ergopower: Introduced thumb-paddle indexing alongside drop-bar brake integration.
- SRAM Grip Shift (MTB): Popularized indexed twist-shifting in mountain biking.
- Shimano STI Levers: Merged braking and indexed shifting into a single control interface.
- SRAM DoubleTap: Single-lever dual-shift indexed system for road bikes.
- Di2 & AXS: Digitally actuated versions of indexed shifting using servo motors.
Related Terms
- Friction Shifting
- Derailleur
- Cable Pull Ratio
- Gear Indexing
- Shifter Mechanism
See Also on BBB
References
- Shimano Technical Documentation Archive (SIS, STI)
- Campagnolo Historical Timeline
- SRAM Product Support: Cable Pull Specs
- Park Tool: Indexed Shifting Adjustment
- Sheldon Brown: Friction vs Indexed Gear Systems
- Bikerumor: A Brief History of Shifter Evolution