Prototype SRAM BlackBox Derailleur
Spotted on the back of Aaron Gwin's Specialized Demo 8 Carbon race bike today during practice for the Fort William World Cup, this prototype XX1-style derailleur is actually the second functioning generation of the concept. It employs the same 'straight parallelogram' geometry that sees it move straight across the cassette rather than at an angle, as well as the 'Type 2' clutch system that limits chain slap and the chance of derailment. While there isn't much info on the prototype at this point, it is safe to say that it also features a shorter P knuckle - the segment between the cage and parallelogram, similar to that of the standard X0 DH derailleur - that allows the upper pulley to track a tighter range DH cassette closer for more consistent action. The derailleur was only spotted on two other bikes: Steve Smith's Devinci Wilson Carbon and Sam Hill's Nukeproof Pulse. Is this a DH-specific prototype, or what we can expect the upcoming X01 derailleur to look like?
We've had nothing but good things to say about SRAM's XX1 drivetrain
that we've been using for the last six months, but we also wondered how long it would be until SRAM applied the same principles employed in the XX1 derailleur to a downhill specific unit. After all, the XX1 rear derailleur concept was originally conceived purely for DH use where the bikes use only a single chain ring. The thought was that current rear derailleurs must also handle duties as a consequence of having multiple chain rings: that is, take up the extra chain slack, or allow for enough slack to shift up to the big ring. Eliminate those two jobs and the rear derailleur can be optimized strictly for rear shifting. That early prototype featured a 'straight parallelogram' that moved directly across the cassette, unlike the angled, 'slant-parallelogram' design found on all modern derailleurs. The slant parallelogram is necessary to keep the derailleur's upper guide pulley close to the cassette cogs while the pulley cage is busy trying to reel in and pay out excess chain as the front changer is shifted between chain rings.
Gwin's bike was also sporting a trick seven speed cassette that looks to use the same 'X-DOME' technology as the current XX1 unit, and it is hard to tell if the one on his bike isn't just a trimmed down version of a production XX1 cassette. The cassette uses an inner guard, quite clearly a one-off unit in the photo shown below, that helps to keep the chain from jumping off into the spokes on fast, rough terrain. It has been very interesting to see the progression of these downhill specific compact drivetrains over the last few seasons, beginning with
the six speed gearing pioneered by Jason Chamberlain and Brandon Sloan of Specialized for Team Monster Energy - Specialized in 2010. Yes, cut down cassettes are nothing new in the downhill world, but combining a smaller than usual chain ring with a pint sized nine or ten tooth cog, as well as the freehub that allows the system to run such a small cog, has changed drivetrains on the World Cup circuit for the better.Prototype RockShox BlackBox Charger Damper in the BoXXer
We were very impressed with the action of RockShox's new Pike fork when we first put time on it in Sedona, Arizona, earlier this year, with much of our praise being heaped onto its sealed 'Charger' damper. All of RockShox's current lineup, excluding the new Pike and the BlackBox BoXXer forks shown here that also use the Charger damper, utilize some variation of an emulsion-type damper - this refers to a layout where the damping oil is free to mix with air in the system. Open bath dampers from Marzocchi would fit into this category, as would RockShox's Mission Control damper that they use in their BoXXer and Lyrik forks, as well as FOX's Open Cartridge found in their Evolution series. In an emulsion damper air is used to compensate for damper shaft displacement as the fork compresses and extends. Oil does does not compress, meaning that the fork would not be able to compress if the leg or cartridge body were only full of oil. This design is often simpler but can mean that the oil and air can mix enough to cause the resulting air bubbles to pass through the damping circuits, resulting in a loss of damping and control. The opposite of the above, a closed and pressurized damper like the Charger system is completely full of oil and has essentially no air within it, meaning that there is far less opportunity for it to foam during hard use. It makes a lot of sense for RockShox to drop this type of damper into their downhill race fork given that this is the sort of environment where suspension is pushed to the max.
But how does the damper compress if it is completely full of oil? In order for a closed damper to work, it must utilize some form of compensator that allows for expansion under compression - picture the internal floating piston (IFP) in the piggyback of a rear shock that pushes against the air trapped on the opposite side of the oil, thereby allowing for oil displacement. Rather than an IFP, the Charger damper uses an extruded rubber bladder to accomplish the exact same task, with the bladder expanding as the damper shaft travels into the cartridge as the fork compresses. Again, this isn't a new idea, but it is one that makes a lot of sense within a fork because a bladder does not present any of the friction and packaging issues of an IFP design.
The photo above shows a Charger damper from a Pike fork, but the concept and layout of the version in the BlackBox BoXXer forks are likely very similar.