An interesting read: Shimano’s Shifting Philosophy We were given a fresh explanation of Shimano’s drivetrain philosophy at the launch, which actually made sense. Shimano divides all available gear ratios into two groups: “Driving gears” and “Challenge gears.” Driving gears, in the case of a two-by or three-by transmission, are in the middle range of the cassette when the rider is in the big chainring. Challenge gears are for the steepest climbs, when the rider is forced to select the smaller chainrings and to use the larger three cogs of the cassette. In the case of a one-by drivetrain, Driving gears are the first eight cogs on the right-side of the cassette. Shimano professes that the smooth, 10-RPM jumps between shifts generated by its Rhythm Step, 11 by 40-tooth cassette, optimize the efficiency of the driving gears that we use most often for both climbing and pedaling on the flats. While the closer gear ratios of Shimano’s XTR cassette provide smaller steps between most of the gearing range, they cannot attain the higher top and bottom gears of SRAM’s XX1 10 by 42 cassette. To achieve a competitive spread, Shimano “strongly suggests” that XTR customers choose its two-chainring option. Before you whip out your calculators, the closest comparison that a Shimano XTR M9000 two-by drivetrain has to SRAM’s one-by is: Shimano 28 x 38-tooth chainrings, two-by drivetrain: Lowest gear 28/40 = 1.42:1 ratio. Highest gear 38/11 = 1:3.45 ratio. (22 gear selections) SRAM 30-tooth chainring, one-by drivetrain: Lowest gear 30/42 = 1.4:1 ratio. Highest gear 30/10 = 1:3 ratio. (11 gear selections) What the above chart demonstrates is how Shimano’s close-ratio two-by option provides a nearly identical gearing spread when compared to a SRAM XX1 one-by drivetrain. By switching to a 28-tooth chainring, the SRAM one-by drivetrain can also match Shimano’s 26 by 36 option, but Shimano also offers a third, 26 by 36 option for its two-by crankset that provides XTR customers a lower granny gear than SRAM can match (Shimano: Lowest gear 24/40 = 1.66:1 vs SRAM: Lowest gear 28/42 – 1.5:1). The bottom line is that Shimano’s choice for trail gearing is a two-by transmission, and it competes directly with SRAM’s one-by offerings. The customer’s choice is: “Do I want 22 shifts and a front derailleur, or do I want 11 shifts and no front derailleur?” What about Shimano’s One-By XTR Option? One-by customers can choose XTR chainrings between 30 and 36 teeth, but the narrower gearing spread of the 11 x 40, eleven-speed cassette means that riders may need to keep a couple of chainrings in their toolbox to match their gearing to the task at hand. Calculating out Shimano XTR’s lowest-available, 30-tooth-chainring option fetches a low gear of 1.33:1 and a high of 1: 2.73. Compare those figures with the options from SRAM and Shimano that we covered earlier in this segment, and they indicate that hills will be harder to climb, or you will probably be spun out on the flats. Shimano’s one-by gearing options are clearly intended for racers and stronger riders who will probably choose the biggest chainring that they can comfortably push and then suffer with whatever low gear is left when the big climbs arrive. What this says, and its from Shimano themselves, is that their "One-By XTR " option is not anywhere near what SRAM can offer. The 10 x 42 option with SRAM makes more sense vs 11 x 40 from Shimano....unless you like suffering!! this tells me that SRAM is the only option for a single chainring as their spread is better. Shimano still needs two up front or you buy extra Chain rings to swop out if the ride is challenging
