29er, Fork, Forks, inverted, RockShox, RS-1, Sea Otter 2014, Sea Otter Classic - April 17, 2014

First Ride: RockShox RS-1 inverted fork

We got a ride on the new RockShox RS-1 inverted fork at the Sea Otter Classic last week and came away pretty impressed by its smoothness, suppleness and responsive steering. Much of its performance success can be attributed to its so-called “upside-down” design. Though inverted forks have many advantages and are commonplace in the motorcycle world, widespread success has eluded the design in the bike market to date. RockShox hopes to change that with its new RS-1 29er cross-country superfork.

Why go inverted?

The advantages of an upside-down fork include a stronger, stiffer upper which produces better steering and reduces flex. The sliders are also closer to the ground so there is less leverage, friction and wear on the seals during use. With gravity constantly feeding oil to the seals, they remain lubricated which adds to the fork’s smooth operation. Though less dramatically than on a motorcycle, the inverted design produces less unsprung weight with only the sliders and axle going up and down instead of the whole fork leg. This makes the fork more supple and reactive to bumps.

What’s made the inverted design such a challenge for bicycles is balancing the amount of material weight necessary against torsional stiffness requirements. Since there is no fork arch holding the two legs together, independent leg movement has been an issue in past efforts, and forks tended to be flexy and not steer well. To compensate, manufacturers tried adding material and increasing diameters, but were left with forks too heavy to be viable.

Technology to the rescue

RockShox has had an inverted fork on the drawing board for several years now and only recently has their technology advanced to the point of making the design a reality. The first technology is carbon fiber and the processes RockShox has developed to create a one-piece fork upper, steerer tube, and crown. With its Formula 1-like lines, the RS-1’s upper molding is a sight to behold, and in your hand it’s equally impressive to feel—stiff and strong, yet feather-light.

The other key innovation is what RockShox calls Predictive Steering technology—a hub and axle system that locks the independent legs in place and compensates for the lack of an arch. A massive 27mm axle called the Torque Tube runs through the proprietary hub and connects the two 32mm stanchions to create a stout, stiff brace that holds it all together. A 15-millimeter Maxle Ultimate thru-axle is used to press the fork dropouts against the knurled ends of the Torque Tube making a connection that’s massively stiff and budge-proof.

New internals

With the flex issue solved, RockShox turned their attentions to the fork’s internals and created the new Accelerator Damper. The circuit keeps air and oil completely separate for more consistent performance, while the remote-only lockout uses a floating-piston design that compresses the oil when activated resulting in a firmer lockout—an advantage in racing situations like sprints and climbs where power transfer is key. The remote is an XLock hydraulic unit like those used for the Reverb dropper post, and there’s an XLock Full Sprint version that actuates the RS-1 and a compatible rear shock simultaneously.

The damper also includes RockShox’s Dig Valve compression circuit which was created to manage fork dive during successive hits and heavy braking. It also features their Rapid Recovery system to keep the fork riding high, in the plushest part of the travel. Finally, RockShox ported over its Bottomless Token air-volume spacer system from the Pike to adjust how progressive the fork is through its travel.

How costs what?!

With advanced carbon construction, mold-breaking design and souped-up internal goodies, you knew the RS-1 wasn’t gonna be cheap—and at a whopping $1865 it’s more than twice the price of a SID XX. On top of that you need a Torque Tube-compatible front wheel or hub, of which there’s only SRAM’s and a rumored DT-Swiss option. In either case, you’re looking at another grand to get it sorted.

Who is this fork for?

By its nature, the RS-1 is very exclusive and suited only to world-class cross-country athletes. It’s a bit like the Formula 1 auto racing paradigm. We revel in the fact that they develop new technologies to win races even though few of us can afford it. Down the road, we hope the technology proves out, economies-of-scale kick in and we can buy the mere mortals version eventually.

The test ride

We took the RS-1 for a spin on the grassy hills of the Sea Otter XC course and it is indeed an eye-opener. Installed on a 100mm-travel Trek Superfly, the fork felt supple and steered incredibly well. It silenced the braking bumps and chatter of the course’s high-speed downhills and was so lively it invited constant jumping and flicking.

Mated with the new RockShox Monarch Debonair rear shock, the bike felt like it had more travel than it did. In fact, when I mistakenly commented that this “Trek Fuel 29” felt more supple than the one I had at home, a SRAM engineer pointed out that I was not on a Fuel, but a Superfly with 20mm less travel.

The damper is indeed a revelation. With stiction minimized, it enters its travel very smoothly with no abrupt resistance, which translates to a very supple experience. Coupled with fast, responsive shock absorption at the upper part of the travel, plus excellent mid-stroke support and we have an unprecedented XC fork in our midst. The rear Debonair shock has a very similar characteristic where it is very supple in its sagged position. But as it tops out, there is no harsh part in its initial travel that is common to other rear shocks.

Bottom line

Given the advancements, would I buy this fork at $1865 plus the new wheel required for the axle standard? No—it’s too much money for my non-podium abilities and aspirations. But I relish the fact that it’s a better XC racing fork, and that very smart folks are bringing it to market to push the performance envelope. I also appreciate that what’s at the bleeding edge today may be commonplace tomorrow. So while it’s not for me—or probably you—now, someday some version of it might be.

//www.youtube.com/watch?v=62_ezUfo5Co