A full set of wonderful.
If you're looking to upgrade to a one-by drivetrain but don't want to buy the group piecemeal, the XX1 Group with Shimano XTR Brakes is a one-click, eight piece set to get you out and rolling.
The XX1 group is SRAM's top-end of one-by drivetrain. It includes SRAM's GXP crankarms, which are available in two lengths, 170 and 175mm, that have a Q-factor of 168mm. Carbon fiber arms are mated to an aluminum spider that doesn't require finessing to achieve optimal chain placement. They are paired with a 32t X-Sync front ring, which is, of course, interchangeable with either a smaller or larger ring depending on how much you like to grind uphill. The X-Sync rings are machined with variable thicknesses from tooth to tooth, which essentially locks the chain in place to drastically reduce the possibility that your chain falls off while riding.
This groupset includes Shimano's XTR BR-987 Race brakes rather than a SRAM-branded brake. Shimano's brakes have proven to be the choice of riders who rip the trails, and the XX1 set deserves a brake equally as stunning as the rest of the group. The BR-987s are disc brakes and the next iteration of the BR-985. The levers are carbon with titanium caliper bolts. Additionally, the lever received a dimpled surface for superior grip. The levers are positioned lower than previous versions and the movement pivots directly toward the bar, creating a more streamlined interface. While they do not have the free stroke adjustment, they still incorporate the reach adjustment. They also feature an I-spec body to keep your handlebars as clean as the rest of your new one-by drivetrain.
The cassette is SRAM's X-Dome 10-42t wonder. This 11-speed cassette gives you a wide range of gears without sacrificing clean shifting or speed. The gearing is equally spaced so that once you get used to the range, there aren't any surprise jumps in cadence or missed gears. At first, the cassette body might have you looking a bit confused. SRAM eliminated the lock ring in favor of its XD driver body, which makes room for the 11th cog within the width parameters of standard rear dropout and wheel width. With the cassette threading at the base of the freehub body, it creates a more stable connection between the hub and the cassette. And by using the same installation tool that SRAM has relied on for years, this seemingly complicated cassette is actually easier to maintain than any 10-speed. You'll need to make sure that your rear wheel is compatible with the SRAM XD driver body, as some wheels will require an additional adapter.
You'll switch across your 11 gears with the XX1 rear derailleur and XX1 trigger shift. The shifter is similar to those found in the XX groupset. It features a carbon fiber body and lever for lightweight, durable construction. The shifter also uses X-Actuation which deviates from the 1:1 pull ratio of the 10-speed group to provide consistent shifting throughout a wide range of gears. The rear derailleur also received a makeover. Rather than moving in two directions like most derailleurs, it is now limited to a side-to-side movement of the knuckle. What this does is essentially eliminate ghost shifting. Additionally, you won't need a chain guide to keep the chain in place — the combination of X-Sync chainring, machined pulley wheels, and roller bearing clutch keep it taut.
The SRAM XX1 Group with Shimano XTR Brakes is available with two crankarm lengths: 170mm and 175mm. They both come with the same 10-42t rear cassette and 32t front ring.