Unlike the slack rock garden gobblers on the enduro scene, XC race machines are built to balance the ability to handle moderate terrain at speed with a stiff efficiency that still manages to keep weight within reason. Given that it ticks off all of these requirements, we're not surprised to see RockShox's peculiarly inverted RS 1 ACS Solo Air 100 Fork on more and more 29ers that are hell bent on nothing but taking flight on singletrack. With a stiffer than aluminum carbon fiber upper and profile that tapers to the axles, the RS 1 presents visually as the missing link between rigid road forks and marshmallow DH models. This is fitting, as the overall effect is a more efficient front end that doesn't sacrifice watts or deviate from lines because of fork flex. When you're attacking for a gap or sprinting for the line, the RS 1 also features the firmest lockout of any RockShox fork, so it gets up and goes like a road fork when speed is of the essence. The 32mm stanchions are the same Fast Black coated aluminum populating most of RockShox's line, but they may enjoy smoother travel on the RS 1 than on any of its siblings. Gravity is the fork's friend, as it ensures that the seals are always bathed in oil. This nets increased small bump compliance that improves traction to maintain acceleration across trail furniture. It also yields less stiction to take advantage of RockShox's Rapid Recovery valve system for high speed rebound after full impacts. Consistency equals confidence equals knowing you can take terrain at speed and carry that speed to the brink of big hits without worrying about brake dive. The fork's 27mm Torque Tube axle further increases its stiffness. Torque Tube works in conjunction with a standard 15mm thru axle, spanning the distance between the dropout faces and eliminating end caps. Once the Maxle is tightened, the serrated ends grip the dropouts, effectively mating the axle, wheel, and fork into a front end system that resists torsional flex by ke...