Each individual component in the XX1 build kit has been optimized specifically for single-ring use. At every stop on the component checklist, I found a well thought-out and executed component that worked very well for the application.
The derailleur of the XX1 works a bit differently than other derailleurs. Since it is not designed to work with multiple front chainrings, the derailleur only needs to move horizontally along the cassette. A traditional derailleur moves diagonally—both sideways and fore-aft—so that it can accommodate both the chain slack as you move through the cassette, as well as the chain slack as you change rings in the front.
I do not have more than anecdotal evidence that this translates to a more durable rear derailleur, but I have smacked the XX1 into rocks a number of times now, one of which I believe would have bent every single other derailleur I have ever ridden, and the XX1 has escaped without damage.
My theory is that a traditional derailleur will twist easier than the XX1 with a direct, sideways rock hit, because as a traditional derailleur is being pushed in, it is also being prevented by the rock from moving forward, causing the derailleur to twist fairly easily.
With the XX1, the rock just pushes it in, and the derailleur returns to its place without incident. In other words, unlike a traditional derailleur, the hit does not prevent the XX1 from achieving its regular travel. So no big deal.
The new XX1 11-speed chain features hollow pins and cutout chain plates to keep it light. It is also very thin: 0.5mm narrower than a 10-speed chain.
I have not had any issues with the narrow chain, but it is important to note that if you wind up needing to add a link or two, the hollow pins on the chain do not press in and out. If you cut the chain, I would strongly suggest using a SRAM quick-link to put the chain back together instead of pressing the hollow pin back into the chain. If you do, it’ll break when you go ride.
The shifter is, in essence, an updated SRAM XX shifter with 11 shifting detents. It is very smooth and positive in feel, in contrast to the light and vague feel from the XT shifter that it replaced.
The XX1 shifter also has a pretty wide adjustment range to its barrel adjuster, which I appreciated since it helps to keep the shifting tight as the cable stretches through use.
Cranks and Spider
The XX1 crank is offered in three lengths (165mm, 170mm, 175mm) and two Q factors (156, 168). (“Q factor” is the distance from the inside of the pedal to the center-line of the frame—basically, how wide the cranks are.)
The 168mm Q factor is the standard width for most modern full-suspension bikes, while the 156 Q factor approximates a road bike width.
The narrower 156mm Q factor provides a slightly more efficient pedal stroke, but you may run into clearance issues with some 29’er frames with short chainstays or boxy full-suspension designs.
The 168 Q factor will feel slightly more stable and planted while descending relative to the narrower cranks.
I elected to run the 168 Q factor in the 175mm crank arm length.
The XX1 crank arms are, as far as I can tell, the same as the SRAM XO cranks, just with a different spider and chainring. It is worth noting that the XX1 spider and chainrings are available separately, so if you happen to have a SRAM crank with a removable spider, you can set it up with the XX1 gearing on the front.
Additionally, the XX1 chainring is compatible with 10-speed drivetrains, so you can easily stick a XX1 crank or chainring on their 10-speed setup if you wish.
Perhaps the biggest story with XX1 (outside of its massive gear range) is the wide-narrow chainring profile. When you look at a chain, there are wider sections interlinked with narrower sections:
SRAM has mated the chainring to match these alternating wide-narrow buddies in an effort to add chain retention on the ring. And this they have definitely succeeded in doing.
Just pulling the chain off the crank when removing the crank from the bike requires a good bit more attention. The first three times I tried to slide the chain off the ring, without paying close attention, the chain popped right back onto the ring rather than easily falling off as it would on a normal single-speed chainring. I had to actually think about what I was doing to make the chain come off. It really does work.
So far I have run the XX1 with and without a DH-spec MRP G3 chain guide. I have not dropped the chain without a guide, though the highest speed / roughest trails in the Wasatch have yet to open.
But given that the bike I have set up with XX1 is also equipped with a 180mm coil-sprung fork, 8” DH brakes, and will see near-daily use at the local shuttles and lift access DH trails, I will probably leave the chain guide on all summer just for peace of mind. But for fast trail riding on a ~160mm travel bike, I really don’t feel that a chain guide is required.
In short, the chainring design just works. Really, it works well enough that my guess is within one to two years every single chainring designed for single ring use will follow SRAM’s lead and feature wide-narrow teeth. The only limitation to the wide-narrow chainring is that it requires an even number of teeth. No 33t rings. C’est la vie.