Most inventions don’t arise from one singular leap in technology, but rather from a coordinated or sometimes coincidental union of multiple smaller steps. We have several such steps to thank for today's single-ring drivetrains. Perhaps the most significant is what's commonly known as the 'narrow-wide' chainring, the first of which was SRAM's X-Sync.
The original principals of X-Sync were first conceived at SRAM's offices in Schweinfurt, Germany, not far from the birthplace of 120-year-old powertrain manufacturer, Sachs, whose bicycle division SRAM acquired in 1997. The project that would become X-Sync began with a quest to solve a common, everyday problem faced by common, everyday riders. Unlike mountain bikes, many urban and commuter bikes have been using single-ring drivetrains for decades, especially in Europe. But with no guide or front derailleur, single-ring systems tend to have problems with chain retention. One way SRAM addressed the issue was by experimenting with unorthodox tooth shapes and sizes. After several prototypes using taller, rounder or squarer teeth, an early form of X-Sync eventually emerged from those experiments.
The core design characteristic of X-Sync is the alternating thicknesses of its teeth, which synchronize with the alternating thicknesses of the links in a bicycle chain. The resulting tighter fit significantly limits the chain's side-to-side play that could otherwise derail it. But again, that’s only the core of its design. X-Sync addresses issues riders have with mud, wear and even backpedaling.
SRAM's pedigree in chain and gear design helped its engineers develop the first modern mountain-bike doubles in 2009. These systems combined a wider-range cassette and more useful chainring sizes to encourage riders to stay in one ring for more of their ride. The approach inspired some to ditch their front derailleurs entirely, but even the then-new 10-speed cassette wasn't enough to make a single front ring a practical option for most riders or on most terrain. One-by-11 was developed to be that option. In its early development stages, 'one-by' was actually intended to be used with a lightweight, low-drag chainguide. The inclusion of X-Sync technology changed that, and a lot of other things with it. Besides the fact that it is nearly impossible to derail a chain off these rings, the chain runs quieter than when on traditional teeth. Also, SRAM has ported the technology to the derailleur pulleys for more precise tracking and less rattling. But perhaps the most important perks that X-Sync has brought us lie beyond the gear itself.
If the new wave of one-by drivetrains had required a chainguide, the concept likely would not have dominated component design and bike spec to the extent that it has. Had one-by not been as universally accepted, fewer bike brands would be designing their bikes around it. The simplicity that the narrow-wide ring introduced has uncluttered our handlebars, made our suspension more efficient, our tires wider, our geometry tighter and our rides better.