The bike has unique tension adjusters built into the dropouts. Brown was equipped with a few "cog" options so he could make a final gearing selection at the race once he saw the course. The bike was built off a standard Trek XO2 cyclo-cross platform and had the rear dropouts and chainstays replaced to accommodate the belt. The chainstays are off a Trek T900 tandem; their heavier gauge minimizes lateral flex and compression loads that could make the belt skip.
Trek's Advanced Concept Group has been tinkering with how belt drive bikes can fit into the line. Right now belts are on a few commuter models (including the Trek District) and some other prototypes running around the office but watch for them on more and more bikes in the future.
According to Trek's brand manager Scott Daubert, the dropouts are eccentric.
"If you are familar with Trek's ABP suspension set up you understand how it works," he said on Trek's "Up The Road" blog. "The inboard eccentric plates are slotted to accept a conventional hub. A "QR" threads in from the non-drive side and pinches everything together."