SRAM launches 20-speed mountain bike group

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By Matt Pacocha

You’ve heard the rumors about SRAM XX. There’s been speculation about how many speeds it would have, what gear combinations would be available, how light it would be and what it would be made of. Now we have all the answers. XX is SRAM’s first complete off-road group, featuring an industry-first 10-speed mountain bike cassette and the first double-ring crankset from a major group manufacturer.

Many of the rumors were wrong. SRAM didn’t adopt the Double Tap shifting mechanism from its road components. Nor did it bring out a Zipp mountain bike tubular. The new group does incorporate a modified PowerDome-style machined steel cassette, called X-Dome —  something many didn’t expect because the Red PowerDome cassette clogs in the mud when used for cyclocross.

The biggest surprise may be a remote fork lockout. Just about everyone assumed it would be cable-actuated, when, in fact, it’s hydraulic.

Where does SRAM XX fit?

SRAM brought its four off-road brands — Avid, RockShox, SRAM and Truvativ — together to create a system of top-of-the-line parts meant for the highest level of endurance mountain bike racing. The group’s technologies should be just as useful to the weekend warrior who does a lot of pedaling.

Make no mistake, it isn’t limited to the hardtail crowd. It’s a viable option on bikes using the XX suspension line, which includes SID, with 80-100mm of travel for cross-country racing; Reba, with 80-120mm of travel; and finally, Revelation, with 120-150mm of travel.

First and Foremost

The eight-piece group, minus suspension components, weighs less than 2,300 grams according to SRAM. That is substantially lighter than any other group.

Amazingly, almost every part, save the crank, can be installed and adjusted using a T25 Torx driver. The parts we rode and experienced were considered “Level 1 preproduction;” they were made on production tools and are 99.8 percent the same as what will be sent to bike manufacturers in July.

The Drivetrain: Smooth Stuff

Ok, it’s two-by-ten: we’re over that hump. But it’s really smooth. If it were two-by-nine and this smooth, we’d be singing the same praises.

Ron Ritzler, SRAM’s mountain bike category manager and the group’s lead developer, said having the fastest front shifting was a primary goal. First impression is they’ve met it.

There are a number of new technologies that Truvativ, SRAM’s crank division, developed to get the shifting performance. X-Glide is Truvativ’s new front shifting technology that pairs the small and large front chainring tooth combinations using a common denominator of 1.5. This allows the chainrings to be partitioned into equal segments. Each ring combination (26/39, 28/42 and 30/45) has four pick-up points for the chain, and four release points. These eight points are made up of ramps and pins that create “sweet spots” where the chain can stretch between the small ring and large ring while chain rollers remain solidly seated on each.

There are four of these sweet spots on each ring combination. Two are aligned parallel to the crank arm to aid downshifts. Two are aligned perpendicular to the crankarm for up-shifting, even with large loads.

This technology was created 12 years ago, patented and never used because of the need for specific chainring combinations. When the chainring sizes were being selected for XX, engineers started with 28/42 and 30/45. The developer of the sweet spot technology heard of it and reminded the XX team of his design and it was integrated.

The chainrings are CNC machined from 7075-T6 aluminum billet; the thickness desired and the material hardness would not allow for the coined construction Truvativ uses for its other groups. The aluminum is machined down to 6mm at the bolt circle for stiffness, but tapers out to the precisely placed shifting chamfers, gates, pins and ramps at the outer edge. By comparison, Truvativ’s Noir crankset has 4mm thick chainrings.

The outer ring’s taper gently guides the chain down to the small ring, instead of dropping it. There are no chainring nuts: the four outer bolts thread into the chainring and the inner ring’s bolts thread into the crank. In the name of stiffness, the XX crank and chainrings rely on a new proprietary bolt circle diameter of 80mm/120mm, which places attachment points as close to the chainring teeth as possible.

The chainline (measured to the middle of the two rings) is 49.5mm, down 2mm from Noir’s 51.5mm (measured to the middle of the middle ring). Narrowing the chainline allows all of the rear cogs to be used from the large chainring.

The majority of SRAM’s introductory XX athletes use the 28/42 combination, save for the Gary Fisher duo of Jeremy Horgan-Kobelski and Sam Schultz, who use the 26/39-tooth combination due to their use of 29-inch wheels.

Q-Factor is another huge consideration of the XX crank design. The standard GXP and BB30 XX crank options measure 156mm. This is a dramatic 17mm narrower than the standard Noir crank. It’s something racers have begged for and its benefits can be felt immediately.

The only problem with the narrow dimension is that it doesn’t fit every bike. To that end, Truvativ has manufactured a 164mm BB30 option and a 166mm GXP option to accommodate frame variance. These additional cranks feature the same 49.5mm chainline. For Truvativ, however, it meant separate molds had to be manufactured, showing a serious commitment to accommodate frame designs. Still, some bikes are incompatible. Santa Cruz’s new Blur XC carbon is a notable non-conformist due to the position of its lower linkage.

The four XX cranks — standard GXP Q-156, BB30 Q-156, BB30 Q-164 and GXP Q-166 — are available with two bottom bracket spindle sizes and four bottom bracket cup options.

For the standard 24mm steel GXP spindle, there are two bottom brackets: a standard thread-in version and a press-fit version. The press-fit fits Shimano-designed 86mm threadless bottom bracket shell used by Giant, Pivot and Scott, among others.

The second spindle size is the 30mm diameter BB30, whose spindle is made from aluminum. For this option Truvativ also offers two bottom bracket types: standard BB30, which relies on a machined shell that accepts c-clips and press-fit bearings; and a new PressFit 30 design. PressFit 30 system eliminates the precision tolerances required from the frame manufacturer. Instead of requiring c-clips and exact tolerances to directly house the bearings like BB30, the PressFit system is a self-contained bottom bracket where the bearings are housed within resin cups and well sealed. The whole unit presses into an oversized bottom bracket shell and promises quietness.

All four of the bottom brackets feature hybrid ceramic BlackBox bearings.

The XX cassette builds upon the Red group’s PowerDome cassette, with a technology called X-Dome. It’s available in two combinations, 11-32 and 11-36 — with eight of the cogs machined out of a solid hunk of 4140 chromoly steel and the lowest cog made from 7075-T6 aluminum. The alloy cog is replaceable as it is press-fit to the steel block of eight cogs; it also makes up the back plate of the cassette. The 11-tooth cog is separate and the whole unit is held on with a 7075-T6 aluminum lock ring.

You’ll immediately notice that the cassette is hollowed; this saves weight (the 11-36-tooth weighs just 208-grams and the 11-32-tooth is a featherweight 185-grams), and allows mud to flow through. The entire manufacturing process, including machining, quality checks and finishing is said to take nine hours per cassette.

The X-Dome cassette features conventional ramping and has none of the missing teeth of the road Open Glide cassette. The design is extremely quick shifting and quiet; in fact, even with our limited experience we’d say it’s quieter than SRAM’s road drivetrain.

SRAM did not develop a dedicated chain for XX; it recommends its 1090R or 1090 chains.

Transmission: Exact Actuation

XX uses the same constant cable-pull shifting technology as the road groups, dubbed Exact Actuation. This means that the XX rear derailleur and cassette are compatible with the road shifters.

The shifters use the same two-trigger system as X.0 parts, redesigned to be smaller and lighter. The shifters feature adjustable carbon fiber cable-pull paddles.

The front derailleur’s steel cage is shaped for double chainrings. There are more than 40 variants, including-high mount, low-mount and four different direct-mount versions. There are options for the clamp size, cable-pull direction, and for different chainring combinations in the direct-mount configuration.

The 181-gram XX rear derailleur is all new, albeit drawing heavily on the X.0 design. It features a magnesium forging for the rear linkage and cable guide fin. Compared to the X.0, it has a new cable-fixing mount, refined pulley placement and 93mm cage to accommodate a 36-tooth cog and double chainrings. It features a titanium spring and hybrid ceramic pulley bearings. Its hardware is a mix of aluminum and titanium featuring T25 Torx heads to reduce the potential for stripping.

Brakes: Superlight Stoppers

The XX brake spawned the already released Elixir CR Mag, even though the latter was shown to the public first. The 288-gram (front, direct-mount with rotor and hardware) brakes feature Avid’s TaberBore technology, which promises more power and modulation than previous Juicy designs.

The XX brake is a whopping 55 grams lighter than a Juicy Ultimate and features tool-free pad-contact adjustment. The caliper is a two-piece clamshell of forged magnesium. Avid engineers feel that they can make a stiffer, lighter caliper using two halves, rather than a single forged body.

Pads are made of an organic friction compound, the same as the Juicy Ultimate, fixed to alloy backers. Three rotor options are available: 140mm rear, 160mm and 185mm. All mate a steel braking surface to an aluminum carrier with a six-bolt ISO mount. The rotors come with titanium bolts.

Avid engineers reduced the weight of the carbon brake levers from 11 grams to 8 grams — almost 30 percent. The brake uses a one-bolt U-clamp and the entire package is fitted with titanium T25 Torx bolts.

Because of the new U-clamp mount, MatchMaker had to evolve to fit the new brake. The new multi-mount system is dubbed MatchMaker X, which offers a greater adjustment range than the original while retaining smart features like ambidextrous mounting for varied positions. The mount relies on a hinged design and one bolt.

For those that use a handlebar remote lockout, RockShox has taken it to another level with a MatchMaker X-compatible hydraulic lockout called XLoc.

The XLoc is a whole story itself. It’s 60 grams lighter and operates more smoothly than the cable-activated version, and is impervious to contamination.

The XLoc relies on a new damper assembly, retrofitable to current BlackBox Motion Control forks, which replaces a crown or cable-actuated unit and works simply. You turn the fork on by depressing the pen-like push button on the remote, opening a gate valve in the damper.

XLoc has an external Floodgate adjustment that works by reducing fluid volume and preventing the gate from fully closing. XLoc is impressive in just about every facet; it’s lighter, simpler and better functioning. The only disadvantage could be failure of the hydraulic mechanism; if you were to tear the line or lose pressure somehow, the damper reverts to the closed, locked-out position.

RockShox will offer four fork platforms with XLoc and XX branding: SID, Reba and Revelation. These platforms have options to accommodate 29-inch wheels (Reba) and thru-axles (Reba, Revelation). RockShox incorporates an XX XLoc option into its reintroduction of the SID World Cup with BlackBox carbon steerer, the SID XX WorldCup.

The XLoc comes with titanium hardware, left or right options and is only compatible with Avid’s Elixir CR Mag and XX brakes.

First Impressions: More than evolution

After spending two days learning about it and close to a half-dozen hours riding it, we can whole-heartedly claim that this group represents more than just an evolution for SRAM and its off-road brands.

Is it revolutionary? We need more time to answer, but it is absolutely impressive. The SRAMies say they put their best and brightest on this job, gave them time, world-class athlete feedback and the freedom to think outside of the box.

My initial impression is that XX is as much, if not more, than you would expect from something developed with these resources. It’s pre-production stuff, yet shifting is incredibly smooth and everything works to what seems to be a professional level.

The surprises are the X-Glide chainring timing, the simple and effective XLoc lockout, the 36-tooth rear cog and the PressFit30 bottom bracket design.

The rest —  including notable designs like the X-Dome and pleasantly narrow Q-Factor — were less of a surprise, but nonetheless greatly appreciated. We came away from SRAM’s XX launch with a strong desire to bring XX to the race course this summer, which may be the best way to test it. For more on SRAM and the path that led to XX, don’t forget to check out our August issue of VeloNews, on newsstands July 7.

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