Sram’s eleven-speed XX1 group will be recorded as a major branch on the phylogenetic tree of mountain bike evolution, essentially changing the way we perceive the sport. Everything from riding technique, to suspension design, to bike geometry will be influenced by the one-by system. Only doing away with the external-transmission drivetrain altogether would have a bigger impact than eliminating the front derailleur (anyone else think that’s what Shimano is perfecting before answering Sram’s 1×11 salvo?). X-Sync chainrings are a major part of Sram’s eleven-speed puzzle, increasing chain retention and drivetrain efficiency at the same time. What’s the difference between XX1 and X01 rings? Should you care about X01 chainrings even if you have no intention of buying an eleven-speed group? Yes, dear reader, and here is why.
Machined from 7075-T65 aluminum, which has strength similar to steel but is obviously much lighter, X01 chainrings are nearly identical to their more expensive XX1 siblings. Sharing the same X-Sync tooth profile (narrow-wide in the parlance) and stiffness-enhancing shape, the only practical difference between X01 and XX1 rings is their BCD (bolt circle diameter), with XX1 offered solely in a proprietary 76mm and X01 presented in both common 104mm and proprietary 94mm BCDs, the latter allowing chainring swaps without the removal of your crankset.
X-Sync technology alternates narrow and wide width teeth, which fit into the alternating narrow and wide links of a chain, helping to prevent chain slip. Additionally, since the chain never shifts between chainrings, there is no need to compromise between easy chain derailment and tenacious engagement, so teeth are machined taller for better retention. While Sram’s competitors have recently entered the market with 1x chainrings that mimic Sram’s tooth profile, in our experience the Sram rings offer the best chain security.
Both of X01’s 94 and 104 mm BCD rings are cheaper to produce than the 76mm BCD XX1 rings, which keeps a bit more cash in your wallet, but the real savings is to be had with the 104mm version. Since the common 104mm BCD crank is probably what you are running right now, there is no need to buy an X01 crank, as nice as they are. Simply bolt up the universally-sized ring and, bam, you just saved enough money to get yourself an X01 shifter and chain.
Additionally, if you are thinking of converting to a one-by-ten drivetrain, using a 104mm BCD X-Sync X01 chainring provides two advantages. One, you’ll be a step closer to your eventual eleven-speed conversion (these rings work great with 10-speed chains even though they are designed for 11-speed chains). Two, with a high-end clutch derailleur—Sram’s Type 2 or Shimano’s Shadow Plus—you will virtually eliminate dropped chains, even without a chain guide. When combining the clutch-equipped X-Horizon X01 derailleur with an X-Sync chainring, chain retention devices are completely unnecessary—your chain is staying glued to the chainring. X01 chainrings provide all of the performance advantages of XX1 rings with a negligible weight penalty, while costing a little bit less, and offering the convenience of a universally applied 104mm bolt circle diameter.