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RockShox 2012 SID 29 XX Suspension Fork
The RockShox SID 29 XX fork is installed on my Moots MootoX RSL hard-tail 29er mountain bike. It is a good match for the MootoX RSL, with its light weight and race-oriented performance. I wanted a QR15 fork with an 80mm travel option and remote lockout, so my options were limited.
Great for big bumps, ineffective on the small stuff
While it soaks up the big stuff very well, to prevent bottoming-out the RockShox SID 29 XX on rough terrain required a fork pressure of 170-180 psi (I weigh 172 pounds). That pressure leaves about 3/8" between the rubber ring indicator and the top of the fork after an aggressive descent.
With some experience, I found that a pressure of 150 psi was perfectly fine, and did make the fork more compliant on lumpy ground, but it would bottom out more often on big hits— fair trade.
On lumpy uneven ground and little bumps, the SID 29 has little suspension effect, making for a rather jarring ride by comparison to forks with larger air chambers, or my Fox F32 on my Moots YBB 26. I cross-checked this behavior by riding with the SID 29 locked out and not locked out and could scarcely tell any difference at all!
Dropping the fork pressure to 150-160 psi is a reasonable compromise provided that one is not expecting big “hits”. This provides a modest increase in comfort over 170 psi.
In short, the SID 29 is NOT a plush fork, at least not if one sets the fork pressure to a value that prevents bottoming out on the rougher terrain. Riders looking for a plush trail biking fork should probably be looking elsewhere.
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Weights as weighed (not from specifications) on my gram-accurate OHaus lab scale.
The big deal with the 2012 RockShox SID 29 XX fork is a weight reduction so that it weighs little more than a fork for 26er.
Two versions as actually weighed. The SID XX World Cup with carbon fiber tapered steerer saves 177 grams = 0.390 pounds. However, the headset required adds additional weight, perhaps 50g, so the net weight savings is likeliy only on the order of 130 grams or so.
SID XX (aluminum steerer)
1687g = 3.72 pounds 15QR skewer: 71g = 0.157 pounds = 1758g / 3.87 pounds with 15QR skewer
SID XX World Cup (carbon fiber tapered steerer)
1510g = 3.32 pounds 15QR skewer: 71g = 0.157 pounds = 1581g / 3.485 pounds with 15QR skewer
SID XX World Cup tapered carbon fiber steerer
Installation of a SID XX World Cup carbon fiber tapered steerer on my Moots MootoX RSL slackens out the geometry just a bit, and requires a headset with outboard (larger diameter) bearings. The straight steerer on the regular version uses a bearing internal to the head tube. In both cases I used a Chris King headset.
Click for a larger image, and see discussion below.
Initial riding impressions (same bike) are that the carbon fiber steerer improves the front-end stiffness and steering precision, but this apparently contradicts what RockShox says about the XX World Cup version being slightly less stiff. But that article is not clear on what’s being compared. I will be clear: straight Al steerer to tapered carbon fiber steerer. There is also quoted a “testing tolerance of 10%”, which all but eliminates the claimed differences.
Perhaps the larger diameter outboard bearing compensate for the minor difference in fork stiffness.. Without swapping forks again, it’s very hard to compare, but my impression remains firm in this regard.
Click for a larger image.
RockShox SID 29 XX Remote lockout
Kudos to RockShox for offering a remote lockout in a 29er fork, since Fox doesn’t even offer a remote lockout option as of this writing in August 2011.
That said, there are usability issues with the RockShox lockout, and I consider it much inferior to the Fox dual-operation design on my 26" fork on my Moots YBB 26:
- The RockShox design is a toggle (in/out) operation, and one cannot tell by feel where it is set. By comparison, the Fox design has one way to lock it out, and a separate way to release it. Unlocking the shock with the Fox design is instant, easy and unambiguous (just twitch one’s hand against a flat plate for a satisfying click that confirms it’s unlocked). There is no such feedback with the RockShox design.
- The RockShox remote lockout has no auditory feedback for locking or unlocking. All one can really do is take one’s eyes off the trail and look at the mechanism— this is not good.
- The RockShox button is quite small, and when I’m bouncing all over the place on a hard-tail MTB, it can be difficult to operate that button.
- Unlike the Fox design, the RockShox design requires that I move my hand inwards on the grip by a good inch or so, which is a very Bad Idea when the going has just become very rough. Granted, I run Shimano XTR, and perhaps a SRAM setup doesn’t have this issue— I don’t know.
- My right thumb has a weak tendon. The type and amount of force required can literally make my thumb hurt by the end of a ride. This is peculiar to my thumb, but the fact is that the Fox F32 design on my Moots YBB 26 incurs no such penalty. Since Fox does not offer a lockout on its 29er forks, one has to be fair: a remote lockout is better than no remote lockout.