Shimano Total Integration (STI) is a gearshift system designed by Shimano for racing bicycles. It combines the braking and gear shifting controls into the same component. This allows shifting gears without having to remove a hand from the bars, unlike previous down tube shifting systems. This component is usually referred to as a "shifter" or "dual-control levers", or occasionally "brifters".
In 1989, Shimano introduced their "Rapidfire" shifting for mountain bikes. This brought indexed shifting to the handlebars - something previously only available on downtube shifters. This mechanism operates like a ratchet, the larger lever applying tension to the gear cable, the smaller one incrementally releasing it. The Rapidfire mechanism was subsequently adapted to be used in STI levers.
In 1990, Shimano introduced their STI shifting levers for road bicycles, which completely integrated the brake lever and shifter. It also redesigned the brake "hoods" where riders commonly rest their hands. This new design worked like a normal brake lever in the longtitudinal plane, but also allowed the rider to shift to a larger cog by pushing the lever so that it pivots laterally. Behind the brake lever, there is a smaller lever that shifts to a smaller cog when pushed towards the inside.
This system helped Shimano take the lead in groupset manufacturing.
Around the same time, the other major global producer in bicycle components, Campagnolo, collaborated with the Sachs company to produce their "Ergo Shifting" system, differing substantially in its design and operation. Ergolevers contain the mechanism inside the main body of the unit, rather than in the top of the brake levers, and there is no sideways action on the brake lever. Instead, the "flipper" that changes to a smaller cog on STI levers changes to a larger cog, and there is a small lever (sometimes called a 'mouse ear') on the inside of the brake hood body that shifts to a smaller cog.
In 2003, Shimano introduced "dual-control levers" or STI for mountain bikes in their XTR groupset. Like the road shifters, XTR used the same lever for braking and shifting. This was met with some resistance as they limited the choice of disc brakes to only those made by Shimano. They are nicknamed, "flippity shifters" for the brake lever's ability to move in the vertical plane.
STI and Ergopower have largely displaced downtube shifting, even though some cyclists still use downtube shifters for various reasons, including less expense, less weight, more flexibility, and better reliability. A compromise is to use barend shifters or Barcons. This type places the shifters closer to the hand positions, but still offer a simple reliable system, especially for touring cyclist. Drawbacks to STI and Ergopower systems include the higher weight, the higher price and the failure rate. There are many more parts in an STI or Ergo lever than in a downtube system.
Since the creation of the STI shifting system the main improvements have included reducing weight and increasing cog count. Weight savings have come from using new materials such as Duralumin in Shimano's component groups and carbon fiber in Campagnolo's parts.
Some cyclists, including Lance Armstrong, install a standard STI shifter on climbing-specific bikes for the cassette and a downtube shifter for the chainrings in order to reduce weight. This is done because chain is shifted across the cassette much more often than the chainrings. This setup might save up to 200 grams (7 ounces) off the total bike weight. Compared to the minimum legal racing weight permitted by the Union Cycliste Internationale, 6.8 kilograms (15 pounds), 200 grams is about 3% of the total weight.
- Road S.T.I. Lever Technology at shimano.com [BROKEN LINK]