SRAM's 12-speed Eagle proves that a one-by drivetrain can match or better the range of a multiple-chainring transmission, which in turn, has doused any hopes that the front derailleur's smoldering embers will ever be rekindled. Eagle was a must for the Chicago-based parts maker, because its premier XX1 ensemble could not match the range of Shimano's sharp-shifting two-by drivetrains, and descriptors like "virtually," "similar to," or "nearly," are not the vocabulary of a winning team. The addition of a 50-tooth cog to its 10 by 42, eleven-speed cassette provides a 500-percent gearing spread, which exceeds Shimano XTR and XT's ranges and thus, should silence all doubters, even the staunchest two-by holdouts in Germany. That twelfth cog, however, may have consequences that reach beyond range and MSRP.
Eagle has only been released at present to a handful of media, racers and OEM customers for evaluation, but all reports have been quite positive. And, in spite of the expected pushback from potential customers who have grown weary of SRAM and Shimano's the cog-of-the-month competition, those who have time on the group have unanimously applauded SRAM for extending the lower gearing range to accommodate fitness levels that fall below professional athletes, without sacrificing top-end speed.
Less advertised, but perhaps more important, is the fact that improved frame geometry, advanced suspension and wider, grippier tires have made today's mountain bikes far more capable climbers, especially in technical situations, where the rider's legs and lungs have become the only limitations to topping ascents once deemed impossible. I am sure that Eagle will be embraced by the sport's strongest athletes when they begin to push those boundaries.
Shimano will be forced to respond, at least with a larger cassette cog, and we anticipate they will also jump to 12-speed as well. Shimano will offer a 46-tooth option and, because their present cassette design restricts their smallest cog to an 11-tooth, barring a new driver design, there is nowhere for Shimano to go except for up. Shimano fans who do not want to wait for the next iteration of XTR can jump ahead of Japan and purchase OneUp's Shark kit, which updates the cassette to a 10 by 50 to equal the range of SRAM's Eagle, and it updates the rear mech with a longer cage in order to handle the extra chain and new cog diameters.
The bottom line is that Eagle is destined for success, and in a short time, we will get used to seeing larger cassette cogs, just as we have learned to ignore wheel diameters and boost-width forks. That said, the acceptance of Eagle will also mark the time when the industry walked away from two hard fought improvements - both of which had profound effects upon the dual-suspension trail bikes we have recently come to know and love.
The first victim is the mid-cage rear derailleur. The long-cage rear derailleur was a product of the industry’s adherence to the triple crankset and the huge amount of chain take-up that it created for the rear derailleur. Riders hated them because the low-hanging cage reduced chain control and made the derailleur susceptible to damage. Switching to two-by drivetrains and later, SRAM's introduction of XX1, made it possible to reduce the length of the cage and the mid-cage derailleur finally became the industry standard. With the debut of SRAM's Eagle and Shimano's extended-range XT and XTR come some of the longest rear-derailleur jockey cages in the history of the sport.
The second loss is more difficult to explain, but it begins with a guy named Bob Girvin, a pioneer suspension designer who patented the forward pivot location of a bicycle's swingarm near the top of a 34-tooth chainring. One quarter century later, nobody has found a better location. Chain tension and the angle that the chain pulls from affects the suspension and how the suspension feels under pedaling loads. Girvin's compromise was to stabilize the drivetrain when it was in the middle option of the triple-cranksets everyone used back then. Girvin knew that shifting to the larger or smaller chainrings would adversely affect the suspension's kinematics, which is a problem that also gives present suspension designers headaches.
By accident or by design, SRAM's XX1 and its derivative one-by-eleven drivetrains stabilized the relationship between the chain and the rear suspension by fixing the size of the chainring almost exactly where Girvin placed it and the XX1 cassette encouraged the rider to keep the chain in the most neutral range of angles in relation to the rear suspension. Shimano's present close-ratio two-by cranksets also maintain that relationship. It can be argued that, in the past three or four years since the relationship between the drivetrain and the rear suspension has been stabilized, almost every long-travel bike made has been a good performer. The trend toward huge cassette cogs may unfortunately reverse that problem by exaggerating the chain angles, and could play havoc with the suspension kinematics once more. In support of Eagle, the angular chain component only occurs when it is shifted into the largest cogs, but those are also the moments when power output, control and grip are highlighted most.
It will be interesting to see how all of this ends up. Suspension designers will be able to tweak their kinematics to compensate for the changes, if needed, and rear derailleurs are pretty robust these days. I find it questionable, however, that after working so long to attain a stabilized drivetrain and instigate the mid-cage rear derailleur standard, that we would throw away both without a care just to widen the bike's transmission ratios. It’s worth considering.