Danny meet XX1, XX1 meet Danny

SRAM’s XX1 groupset is the first dedicated 1×11 drivetrain on the market. A wide range 10-42T cassette is combined with a single chainring up front, while cleverly designed teeth aim to elimiate the need for any kind of chain guide. We’ll be putting it through its paces over the winter to see how it fares, but in the meantime, here’s a quick run down of the build.

Custom SRAM XX1 build on a Specialized Sumpjumper Evo 29er. Click to enlarge

Frame

To hang the XX1 groupset off we were promised something special. Originally slated to be the new Specialized S-Works Enduro carbon, a lack of availability meant that the knee-tremblingly-gorgeous S-Works Enduro became the equally-stunning-but-arguably-more-useable Stumpjumper FSR Evo Carbon 29.

It gets 135mm of travel and a FACT IS9M carbon main triangle with M5 aluminium seat and chainstays. There’s more travel and a slacker head angle than the standard Stumpjumper FSR, meaning that the Evo is designed to excel as the terrain gets that extra bit gnarlier.

We’ve gone for a 34t chainring. Note the asymetric bolt fixings

Chainset

The XX1 carbon crank gets a forged aluminium spider that’s specific to XX1. Look closely and you can see that the four bolt chainring fixing is asymetric. This means it’ll slide right over the crank, and in most cases the pedal, when you want to swap to a different size. The four bolts thread straight into the chainring; so no fiddly female nuts to lose.

Chainring

We’ve opted to start out on a 34T chainring, but should this prove too tall with the 29in wheels, we’ve also got a 32T backup. Chainrings are availble in 28, 30, 32, 34, 36 and 38 teeth sizes.

The key to the X-Sync chainring’s security are the alternating teeth profiles that interlock with the chain links. From above they resemble a sequence of pluses and minuses (+ – + – + -) with the wide, flat minus teeth mating with the chain’s inner link, and the narrower plus teeth interlocking with the outer links. Although the chain can move up and down and side to side over bumps (the Type 2 clutch derailleur does help in this regard), even when it is angled away from the chainring, the teeth won’t allow it to derail. That’s the theory, and so far, in practice, it seems to work.

We can see some people fitting an upper guide for complete security, but we’ll be keeping the chainring fully exposed for the duration of our test.

Another important point to understand is that although the spacing between the 11 sprockets at the back is narrower than 10-speed, the thickness of the teeth are the same. Which means that a 10-speed chain, and by association, your current 10-speed drivetrain, is compatible with the X-Sync chainring.

XX1 chain gets a new coating for improved durability

Chain

Although narrower than a 10-speed chain externally, the width between the inner and outer link doesn’t change with XX1. What has changed is a new coating that SRAM claims is four times more durable. It still fastens with a Powerlink, albeit an 11-speed version, but, unlike a 9-speed Powerlink, it isn’t reusable.

Obviously you have to be conscious of chain length when swapping between chainring sizes. For the correct chain length, run the chain from the chainring at the front to the largest sprocket at the back and pull the two loose ends together without threading them through the rear derailleur. Add two links to the shortest point you can join the two ends and this should be the correct length chain. For peace fo mind, join the chain correctly, let the air out of the shock and compress the suspension with the chain in the largest sprocket. Make sure the derailleur still has some movement left in it and you’re good to go.

X-Horizon rear derailleur offsets the upper jockey wheel

X-Horizon rear derailleur

Most rear derailleurs closely follow the angle of the cassette as the swing towards the spokes. The SRAM XX1 X-Horizon mech moves in a completely horizontal plane. By restricting the movement, loadings are confined to a single plane and SRAM claims the shift force is reduced and shifting speeds are increased. The upper pulley wheel is dramatically offset from the cage pivot so that it maintains a constant gap from the sprockets across the entire cassette.

12 teeth interlock with the chain

Both upper and lower pulley wheels incorporate the same X-Sync alternating plus/minus tooth profiles as the chainring. As a result, SRAM has increased the size of the pulley wheel from 11 to 12 teeth to make it divisible by two.

To reduce cable friction as it enters the rear derailleur, the XX1 mech uses a roller guide.

One of the principle elements of XX1’s improved chain security is the Type 2 Roller Bearing Clutch. This system restricts chain slap by keeping a constant tension on the chain, but still allows the mech to take up slack as you shift. It’s friction based, and it works well, but there is a faint clunk, that’s both audible and tangible through the pedals, as the clutch disengages.

Swing the mech towards the bottom bracket, push the little button marked with a padlock and the mech locks out. This makes it easy to remove and install the rear wheel or break and join the chain.

No need for a front shifter

XX1 Trigger Shifter

With a carbon cover and release lever, Gore Ride-On cable and full bearing mechanism the XX1 shifter is light in action and accurate. However, you do need to set your gears up accurately. Just a small discrepency in cable tension or limit screw adjustment can cause annoying in-gear rubbing. It’s definitely more sensitive to set-up than 10-speed.

Cassette is machined from billet steel, with aluminium 42T sprocket

XX1 Cassette

Arguably the piece-de-resistance of the SRAM XX1 groupset is the cassette. A development of the XX cassette launched a few years ago, this 11-speed 10-42 block is predominantly machined from solid billet steel. Initial cold forging shapes the disc of steel into the cone shown top left in the photo. Then the machining begins; a process that takes around three hours of solid milling time. Still unsure why the cassette costs a cool £329.99?!

To shoehorn 11 sprockets into a standard dropout width without increasing the dish of the wheel SRAM has got creative. At one end it has removed the external cassette lockring and hidden it within the cassette. At the other end the aluminium 42 tooth sprocket is dished to follow the angle of the spokes. It’s clever stuff. Finally, by reducing the spacing between the sprockets, enough room was found.

Only one cassette is available but you can tailor your gearing to terrain, fitness and machinary by playing with the chainring size. By restricting the ratios, SRAM can ensure the gaps between gears are optimsed and the jumps don’t feel too big or too small when you are pedalling. For the record, ratios are 10-12-14-16-18-21-24-28-32-36-42. A 9-tooth sprocket was tested but it didn’t give enough chain engagement and generated an unwanted polygon effect.

The billet steel is cold forged into the shape top left. XD Driver body bottom left

XD Driver Body (freehub body)

SRAM had to redesign the cassette body to go with the new XX1 cassette. The splines on the driver body are much shorter than a regular freehub body. The casette slides onto the body as normal and engages with the splines in any position – most current designs locate in one position only. A standard lockring tool tightens the cassette onto the body. The splines engage with a friction fit that won’t wind into the aluminium as you apply pedal torque.

Most of the major wheel manufacturers are designing compatible XD driver bodies, so you’ll be able to retrofit XX1 to your current wheels.

Components

The remainder of the components are pulled predominantly from beneath the SRAM umbrella. A 740mm wide Truvativ Boobar is clamped by a 40mm Holzfeller stem. There’s a RockShox Reverb seatpost and Fizik Tundra saddle, DT Swiss 1550 Tricon wheels with Maxxis Ardent 2.4in tyres, Avid XO Trail brakes and SRAM lock-on grips. Suspension duty is handled by the new 2013 RockShox Monarch RT3 shock and 140mm travel Revelation RCT3 fork.

Total weight for the bike with pedals is 25.9lb (11.75kg).

Keep an eye out for further updates as we put XX1 through its paces during the winter.