Along with the Velvet suspension fork reviewed last month, X-Fusion (house brand of Taiwanese shock builder to the stars APro Tech) recently sent out a couple of versions of their trail-oriented O2 RCX shocks for us to review.
Like most riders, I haven’t felt the need to monkey much with my rear shocks. Sure there are the usual air pressure and damping adjustments, but given the high cost of custom tunes and replacement units it’s often easiest to find a bike that works well and stick with the suspension designers choices. Nonetheless, I’ve been spending time with both the high- and low-volume versions of X-Fusion’s O2 RCX on my Commencal Meta 5.5 Carbon- and it’s been an eye-opening experience.
The $380 O2 RCX is X-Fusion’s most adjustable rear shock. A multi-position lever provides easy access to four compression damping levels: from essentially open (which I’ll call 1) to nearly-locked (4). Under that (Fox RP23 style) sits an indexed rebound damping adjuster. 
The shock is offered in seven length/travel combinations (ours are 200/51mm) and with a standard (more progressive) or Additional Volume (more linear) air canister.
Having verified the stock shock’s length, travel, and bushing width, replacing the Commencal’s stock RP23 with the O2 was a five minute job. As the trail bike from a downhill-oriented company, the Meta 5.5 is a fun bike- which is the main reason that I bought it. There’s little help in resisting the bike’s desire to get airborne off of every kicker or rail every corner. Still, stock, the bike can feel a bit numb and lost mid-stroke and occasionally gets hung up on ledge-y bits. In my ten months or so with the bike, I never really used the ProPedal beyond level 1 because doing so made the suspension unresponsive to the point of losing climbing traction. All of which is fine- the Commencal is my ‘play’ bike and whatever’s sacrificed on the the way up is regained on the way back down.
When compared to the Boost Valve RP23, the larger-can (AV) X-Fusion felt better on small bumps than the Fox when in its most open compression setting (1). The second and third positions (2-3) were much more useable as well, effectively reducing bob without sacrificing nearly as much small-bump compliance or climbing traction than the corresponding Fox ProPedal levels- though even level 2 can cause unpleasant spiking going downhill at speed. I have found myself using X-Fusion the compression lever more than I ever have with any other shock- open for descents, in the second position for long climbs, the third for dirt road climbs, and the fourth largely on pavement. 
To me, it’s an easier adjustment than that on the Fox. Good- better, even- but not $380 ($430 for the AV) better.
The the standard-can O2, on the other hand, really transformed the Meta from a play bike to much more of an enduro machine. Don’t get me wrong- the 140mm bike would still be very well suited to Moab’s Whole Enchilada or long lift-aided Alpine days- but now it climbs markedly better. Rather than getting lost mid-stroke or blowing through its travel, the X-Fusion (still with 20-25% sag) seems to be more responding more appropriately to any given hit.
Part of the more progressive shock’s benefit is the result of my light (145lb) weight- at lower pressures, any air shock will be more linear than at higher pressures. I was surprised, then, when the bike’s 180lb previous owner hopped took the Meta for a ride and immediately mentioned that the bike rode better. Like me, he felt as though the O2 RCX improved the bike’s feel, making it less likely to hang up on square-edged rocks and more controlled overall.
Given even the lowest level of X-Fusion compression damping’s occasional harshness when descending, the O2 really is best suited to bikes with some level of anti-bob built into their suspension design. On linkage-driven single pivot designs like the Commencal’s, the rider will either need to accept some bobbing or actively use the compression damping lever. 
I prefer the O2 RCX’s damping lever to other designs’ for this reason- it’s easy to vary the amount of damping to work in most situations. Over the past few months, the O2 has loosened up significantly, becoming much more active and requiring ever increasing amounts of air pressure to maintain the same sag levels. Because the shock isn’t losing air, I’m thinking that this is the result of overly tight seals or bushings to start. It is worth keeping in mind that things will loosen up over time when choosing shock.
X-Fusion have simplified the O2 range’s internals relative to other brands’ to make shop or home servicing and custom tunes that much easier. They also feel that this simplicity and the shocks’ construction will pay off with better durability than other brands’. Light damping and slopestyle (lots of damping) tunes are also available. Though I prefer the standard can O2 RCX over the stock RP23 in this application- and the Additional Volume version feels every bit as good with more usable compression damping- the lack of any real price advantage over better-known Fox or RockShox models could make it a tough sell. For anyone looking to replace a rear shock or needing something a bit different tune-wise, though, a call to X-Fusion would be in order. For my part, I’ll be keeping the O2 on my Meta 5.5- and riding the bike that much more because of it. Maybe I’ll even get brave and start experimenting with custom tunes…
marc
