Shimano has added further distinction to their aluminum mountain chainrings beyond merely cut down teeth. The SG-X is their newest design to facilitate quick shifting. The SG-X chainrings were first seen on the XTR cranks.
The outer chainring has four cut notches in the back side, with a 3.5mm diameter steel rivet at their base. A second 6mm diameter rivet occurs 25mm behind the 3.5mm rivet. These two rivets are to lift the chain's outer link plate, during revolution, to the top of the teeth so it doesn't rely just on being shoved by the front derailleur.
The outer chainrings are machined from 4mm thick plate. The middle chainring has four steel "shift gates" riveted to it. The gates are paired with a 44mm on center distance. The gates have a small protruding tooth that grips the outer link plate to lift the chain. To help the chain's journey, the die-cut 2.59mm plate is stamped to make ramp on the back of the chainring that holds the chain in place as the steel tooth hooks the chain. SG-X chainrings come in both 58mm, 74mm, 94mm, and 110mm bolt center diameters. Weights are listed in the accompanying table. $ Price and Sizes Available in Catalog
