SRAM engineering team was clearly very busy making important improvements to this 2012 SRAM Red Exogram GXP crankset. Changes in design and construction techniques yield a crank with increased stiffness and much sharper shifting all at a lower weight.
Exogram technology features new hollow carbon construction which replaces the previous foam core method. The new cranks true hollow section starts in the crank arms and extends into the crank's oversize spider. This new technique maximizes the stiffness to weight ratio. The hidden bolt is another design addition (perhaps borrowed from a certain Italian part manufacturer) in which the crank arm itself effectively replaces one of the arms of the spider so you have four arms with a hidden bolt attaching directly into the crank arm. Again increased stiffness and lower weight.
X-GlideR chainrings are noticeably beefier. The new chainrings are designed for an optimized shifting performance with the Yaw front derailleur. The stiffer rings (5mm 7075-T6 aluminum CNC-machined) feature upshift rivets with an advanced design adopted from SRAM XX with advanced shift timing pins and ramps. CNC machining allows for precision control of each tooth shape, ramp, and nearly every shifting feature of the chainring. Compatible with SRAM/Truvativ GXP bottom brackets sold separately.