Shimano Total Integration
This mechanism operates like a ratchet, the larger lever applying tension to the gear cable, the smaller one incrementally releasing it.
In 2003, Shimano introduced "dual-control levers" or STI for mountain bikes in their XTR groupset.
They are nicknamed, "flippity shifters" for the brake lever's ability to move in the vertical plane.
This type places the shifters closer to the hand positions, but still offer a simple reliable system, especially for touring cyclist.
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.
1. Main lever
2. Release lever
A. Pulling the main lever towards the rider applies the brake
B. Pushing the main lever towards the center of the bike downshifts one, two or three gears depending on how far the lever is pushed (right hand shifter) or changes from a small chainring to a larger chainring (left hand shifter)
C. Pushing the release lever towards the center of the bike upshifts one gear (right hand shifter) or changes from a large chainring to a smaller chainring (left hand shifter)
