For years, the RockShox SID has been considered by most to be the standard for XC race forks. The RS-1doesn’t replace the SID—it takes the XC standard to a whole new level. At a glance, you can see that the RS-1 ACS Solo Air 120 is a completely new direction in fork design. The decision to manufacture the fork as part of a fork/wheel system, dubbed "Predictive Steering," lent to the success of the RS-1 ACS, which was in product development for over three years. RockShox wasn't going to compromise between "good and heavy" or "lightweight and flexible." With advances in carbon technology and a very large and stiff axle, it didn't have to.
The RS-1 ACS is configured to 120mm of travel. Weight-wise it is 1,646 grams (3.6lbs)—incredibly light for an inverted design. Beyond those few "standards," RockShox didn't follow any rules when designing the fork. The tapered steerer tube and crown are a single piece of carbon, which is then bonded to carbon legs. The aluminum threads house the new remote-lockout Accelerator cartridge damper and Solo air-spring. Moving down from the carbon crown and legs, the Fast-Black coated stanchions are 32mm wide. Because of the inverted nature of the fork, the stanchions slide effortlessly — the oil, being above the bushings, provides constant lubrication.
Although the carbon fork is stiff and durable, RockShox wanted to ensure that the robustness extended through to the steering and that flex would not be an issue when railing a banked turn. To that end, working with SRAM, it created a hollow 27mm Torque Tube axle that works in conjunction with a standard 15mm thru-axle. The Torque Tube spans the distance between the dropout faces with no endcaps. This means that once the Maxle is tightened, the serrated ends "grip" the dropouts. This effectively makes the axle and thereby the wheel, a structural part of the fork. This system was given the name "Predictive Steering" and it keeps the stanchion tubes locked in place. This move makes them torsionally immovable so that you won't need to worry about flex.
SRAM (RockShox's parent company) has not licensed the Predictive Steering technology. SRAM and DT Swiss are currently the only companies making wheels that work with the RS-1. There are plans to sell an unbranded hub for sponsored riders, but for now, SRAM features three compatible wheelsets: the Rise XX, Rise 60, and Roam 50.
The RS-1 uses RockShox's XLoc handlebar remote lockout. The addition of this means that external controls are reduced to low speed rebound and spring pressure. For this reason it is ideal for XC riders but doesn't feature the low-speed compression dial that is favored by downhill riders.
As far as the suspension itself goes, the RS-1 features the Solo Air spring. The only difference in this fork is that being inverted, it is pressurized from below. It utilizes Bottomless Tokens to adjust the spring rate. These reduce the volume of the air chamber which in turn, increases the spring rate as you near full compression, this reduces harsh bottom-outs. They are easy to add and remove once air pressure is released by removing the screw cap and threading on the tokens — up to three at a time may be used.
In addition, RockShox uses a Rapid Recovery valve system to create high speed rebound after full impacts. At the same time, it modulates slower rebound speeds and mid-travel. This helps to prevent brake dive and ensure control throughout all stages of compression. The Accelerator cartridge has a spring-loaded damper that compensates for the long shaft as the damper is depressed. The cartridge is serviceable, but requires a long, specialized socket wrench.
Please note that the RS-1 fork is only compatible with Predictive Steering front wheels.