The gear ratios might not make sense, particularly to a roadie, but those last cogs on either end are big jumps. The cogs are the same sizes as on the 10-speed 11 X 36 cogset with the 11T replaced by a 10T and a 42T stuck on the back. The jump from the 12 to the 10 cog on the high end and from the 36 to the 42 on the low end are 20-percent jumps; that’s a lot higher than cogsets have traditionally had. That makes no sense in road use or smooth dirt climbing, but on technical riding, that overdrive on one end or the other is often what we’re grabbing for.
The single front chainring without a guard or front derailleur on it looks so naked out there; why doesn’t the chain fall off of it? Close inspection of the chainring teeth reveals not only that the teeth are much taller than standard chainring teeth, which are low to allow shifting, but also that every other one is a lot thicker than its neighbor to either side. Think about the chain; half of its links are “inner links” with a small (3/32-inch) space between them, but the other half are “outer links” whose space between them is much wider—that same 3/32-inch plus the thickness of two chain plates. So the XX1 front chainring has fat, super-tall teeth every other one (obviously, the chainrings will only be available in even-number sizes) for only the outer links to drop over.
The derailleur jockey wheels also have the same thing — even tooth counts with every other tooth being fat, so the chain obviously will only go on one way. It won’t go onto the chainring or through the rear derailleur without the outer links lined up over the fat teeth.
Despite the tooth thickness and height, the chain obviously is not immune from falling off without a chain guard. But XC racers will always run without a guard because the friction of the chain being pulled up underneath by one, not to mention, the added weight, will be a turn-off for them. Gravity riders will probably make other choices.
SRAM’s mountain-bike product manager Chris Hilton says, “chain guards are like contraception; every person has to decide the level of protection they need for what they’re doing.”
A cross-country racer would probably want to have a few front chainring options for different courses, but in most cases going up or down a couple of teeth will not require a different chain length.
XX1-equipped bikes were all over at Interbike’s Outdoor Demo (as well as a couple of weeks ago at Eurobike), albeit not many rideable ones, since they tended to be the bikes of superstars who had won significant championships on them. But perhaps now you can understand why those riders chose to race with XX1 and why you may find yourself with only a single front chainring sometime down the trail.
Will The One Ring truly rule them all?