SRAM xx1 drivetrain
Posted 203 days ago
On the battleground of bicycle technology, SRAM and Shimano are waging total war. It’s an arms race that sees each company step up shifting performance each year, adding more gears to the cassette and stripping them from the crankset.
In 2009 SRAM launched XX, with a 2×10 drivetrain. Shimano responded with its own 10-speed set-up. Now SRAM has gone one better with XX1, cramming yet one more sprocket into the cassette and ditching one from the crankset, giving mountain biking its first dedicated 1×11 speed drivetrain, available October 2012.
It’s a development derived from rider need rather than simply one-upmanship, SRAM says, giving riders who prefer a single-ring set-up an extra gear rather than trying to shoehorn riders who prefer 2×10 into a more compact system. It does beg the question though, how many is too many? With limited space in the 142x12mm hub standard, will 11-speed be the end of the arms race, the nuclear option? We doubt it.
The new X-Sync chainring is CNC-machined, with alternating wide and narrow teeth to fit smoothly inside the chain’s also-alternating inner and outer links. It’s bound to be a snugger fit, simply because there’s no need to build any shifting ramps into the ring and no need to taper the teeth to allow for it either — look closely and you’ll see they’re square rather than fin-shaped. There are six available chainrings (28, 30, 32, 34, 36 and 38t) to tailor the package to terrain and wheel size.
The chainring fits a universal aluminium spider, meaning you can change rings without removing the carbon crank arm. The system uses BB30 and GXP bottom bracket in wide/narrow Q-factors, with a claimed weight including BB of 650g.
X-Horizon rear derailleur
SRAM has worked hard to keep the chain gap between the top of the upper jockey wheel and the cassette itself constant across all 11 gears. The theory is that by limiting this movement you can experience faster shifting, with more consistent force from your thumb or finger required, and eliminate ghost shifting too. The technology is dubbed the ‘horizontal parallelogram’ by SRAM (see graphic above).
A roller bearing clutch has also been introduced to the mech, to reduce chain bounce and slap. Much like the Shimano XTR Shadow Plus system we saw last year, the Type 2 system will work by making the movement of the mech slightly stiffer — so able to move freely under cable force from the shifters but not so freely under impacts as the bike hits the ground. SRAM says this will have a slight negative impact on ease of shifting, but offers advantages in terms of keeping the chain in place. Unlike Shimano, SRAM has a Cage Lock to make it easier to remove the rear wheel — it doesn’t use a spring and so won’t wear over time. The rear mech weighs a claimed 220g.
XX1 cassette and chain
There’s also a new 11-speed chain, which SRAM says is proving more durable in testing than 10-speed. You’ll also need a new freehub body to mount the 11-speed cassette on (this freehub body can be retro-fitted, or DT Swiss is making new compatible wheels, with more companies coming on board soon, SRAM says). With a massive spread from 10-42t, you’re unlikely to miss the second chainring up front. The X-Dome cassette weighs a claimed 260g.
This is just a taster of SRAM’s XX1 — look out for more in the December issue of MBR, out November 14.