The secret sauce.

At first glance, it looks like somebody at RockShox wasn’t paying attention when they put the RS-1 ACS Solo Air 100 Fork together. The legs slide down over the stanchions, the axle is weird, and the dropouts are, well, weirder. It all seems like a mistake, until you realize that this design keeps the oil suspended above the bushings for better lubrication and smoother compression, boosts the stiffness, and makes the RS-1 ACS one of the best XC forks on the market.

How, exactly? Well, the steerer tube, crown, and legs are all carbon, so stiffness is a given. The stanchions are coated with Fast Black for buttery smoothness, and the axle is basically a two-part job for insane stiffness—there’s a traditional 15mm axle, and a 27mm Torque Tube axle that locks the thru-axle, fork, and wheel into a super-stiff single piece, so you can rail corners with no flex to speak of. There’s a ton of adjustability built into the fork, too, and it comes with an XLoc remote that lets you lock things out without having to slow down. Of course, you need a special wheel and hub to make it all work. RockShox calls this system “Predictive Steering”, and DT Swiss is the only other company to make compatible wheels.

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Smooth Like Butter

  • Familiarity: I've put it through the wringer

If you can't decide between a sid or rs-1, then choose an rs-1. This fork is great. With the fork inverted it keeps the stanchions proper lubricated. The fork feels great and is smooth. Only downside is that your wheel needs a predictive steering hub. It does however stiffen up the front of your bike and improve handling.