Sram XX1 X-Dome Cassette and Drivetrain
The SRAM XX1 X-Dome Cassette builds on the modern marvel of design known as the XG1099 cassette. If you have never seen one of these X-Dome cassettes, they are worth checking out. They are cut from a single piece of steel and are basically hollow, with only a thin skeleton for the chain to ride on.
The design is super light: 260 grams, as opposed to 350 grams or more for a standard alloy carrier-style cassette. The hollow structure allows for awesome mud-shedding while the wheel is spinning, and the use of steel is known for extended durability compared to titanium cassettes of similar weights.
While I don’t have enough saddle time yet to vouch for the long-term durability of the 11-speed setup specifically, I have wrenched on plenty of SRAM Red and XX drivetrains that use the same materials and design, and can say unequivocally that the steel material choice lasts two to three times as long as equivalent weight cassettes built from Titanium (Shimano XTR). Considering the retail price on these things, that is a REAL, tangible improvement.
The SRAM XX1 shifts smooth and positively (in line with all modern, top-level drivetrains) when soft pedaling and being smart with your shifts. But when you’re riding bikes in the mountains, your shifting can get more abrupt and rough—sometimes you need to quickly drop a number of gears for a short, punchy little climb, but you still need to fully load the pedals while shifting three cogs at a time.
The XX1 does this well—comparable to the X0 10-speed stuff I have ridden. It is a bit noisier than the Shimano XT drivetrain I am coming off of, but I’ll take a little noise for the accompanying benefits. Namely…
The large spread in the gearing (10-42) means that while shifting through the middle and low/easy end of the cassette range, I often only need to shift three clicks, where on my old 10-speed setup, I would need to shift four clicks. So the XX1 might be a little louder because it’s moving over a big jump in gears quicker, but the result is that you hit your desired gear earlier, and you can start pedaling hard sooner, which is certainly appreciated on the trail.
The XX1 does require a different hub body for the cassette to ride on, but I have found that these hub bodies are pretty widely available. This is by no means an exhaustive list, but I know for sure that Mavic, DT Swiss, Specialized, Industry 9, Hope, and Loaded all have XX1-compatible parts to run XX1 on their wheels. Chris King is the one big exception for now, though my understanding is that they’re about a year out on their XX1 hub body.
XX1 is SRAM’s flagship product line. It’s their lightest, highest-tech, best-performing offering, and it comes with a premium price tag to match. In my opinion, if that price tag doesn’t scare you off, then the XX1 build kit is really the only option out there right now for a 5-7” travel pedal bike.
The increased gear range, the quickness with which it allows you to hit your gears, the performance of the chainring and derailleur, and the incredible weight and durability of the drivetrain all speak to a very well thought-out and executed arrangement.
A number of the components and design features in the XX1 kit work so well that I am willing to bet that they’ll become the industry standards for all brands in the future.
SRAM has pretty much defined exactly what a purpose-built trail group really is, and has laid out a template for what it should look like going forward.
(You can now read Noah Bodman’s two-part review of the SRAM X1 drivetrain, a more affordable but still highly capable 11-speed system. If you’re not sure you’re ready to shell out for SRAM’s XX1 drivetrain, you should definitely check out the X1.)