The only key difference between RockShox's SID XX Solo Air 100 29er Fork and its more expensive World Cup counterpart is that the SID XX features an alloy steer and crown construction rather than the World Cup's single piece carbon build. It's a little heavier, a little less stiff, and a whole hell of a lot more affordable. Given that very few of us torque hard enough to worry about flex and the SID XX still features the reinforcement of Power Bulge bushings, we think the trade off is a fair one. Despite the change in materials, the SID XX includes the same top end, race ready Motion Control DNA damping system found in the World Cup model. Fighting off gravity and wallow is in this system's DNA, and it uses external rebound and incorporates separate circuits for low and high speed compression. The damping is remotely adjustable with the included XLoc remote, so you can dial it for high riding sensitivity over consecutive bumps or larger impacts to maintain speed across flats and descents and protect the gap you worked so hard to open up on the previous climb. The Solo Air spring is also easy to tune with a single Schrader valve, which adjusts both the negative and positive chambers at the same time, and RockShox's Bottomless Tokens, which alter the chamber's effective volume to dial in the compression curve and meet individual ramp up preferences. Pairing all this with a Rapid Recovery valve that rebounds quickly after full impacts to prep for the next hit means you'll stay in control across root latticed climbs and rocky descents.