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Shimano wasn't first to a 1x12-speed mountain bike drivetrain, a fact that is not only unsurprising nor unexpected. The famed Japanese component engineers are known more for their patience and exacting standards than being first, just as they prize overall performance and unsurpassed durability over light weight. This has been a proven road to success for the company and it's riders, though at times it can feel frustrating. Now with XTR M9100, Shimano has delivered a remarkable 12-speed drivetrain system in both 1x and 2x configurations, with the 1x offering an incredible 10-51 cassette. The efficacy and engineering of Shimano's integration system featuring shifter, crankset, chain and cassette is essential, but no component is more crucial to reliable, precise, and optimal performance than the rear derailleur, which must manage the massive difference between cogs, massive chainline angles, and ultra-precise up and down shifts at all times, under every stress-load imaginable.

The XTR RD-M9100 12-Speed Rear Derailleur was designed to meet Shimano's ultimate goal for XTR M9100 to be the most versatile groupset for XC, enduro and marathon racing. The SGS (Long Cage) version is the only M9100 model that can manage up to the 10-51 cassette, while the GS (Medium Cage) option can run the 10-45. Utilizing sealed bearings in the pulleys and eight flouric coating link bushings, the action and movement in all planes is outstanding- smooth and durable under massive stresses. This is a pure Shadow RD+ design with the slim, efficient Shadow knuckle and cage system, along with the + Clutch for chain control and better 1x retention. The main body is forged aluminum, machined to perfection for strength and weight reduction without sacrifice. The inner cage plate is made the same way, and is complemented by the CFRP composite outer plate, which adds torsional support with less weight. Shimano, known for pulley engineering, moves to 12-speed HG+ compatible 13 tooth models, to better manage the chainwrap and precision shifting required in the tight confines of the 12-speed cassette.

The RD-M9100 models have a conventional hanger mount set-up, not the knuckle-less Direct Mount. Shimano decreased rear derailleur tension at the low gear position, to prevent high chain tension at low gear, which may seem contradictory, but allows the chain to move more freely on and off the largest cassette cog with reduced engagement friction. The engineers also added a bumper at rear derailleur pulley cage to prevent harsh impact and restrict the overall movement only to the necessary range. All adjustment and fixing bolts are stainless steel for complete reliability and corrosion resistance. Finishes are painted or anodized for durability. The move from GS to SGS adds only 3 grams (237g to 240g). The cable-actuated RD-M9100 requires the use of the CN-M9100 12-speed chain and is only compatible with the cable pull of the SL-M9100-R shift levers.

Over the years many riders have professed love and loyalty to the older generations of shifting systems. After all, nothing could be better than 8-speed, right? And yet as riders have needed to upgrade or replace, it is interesting to hear them become loyal to the new products. Is there a real need for 12-speed, with either a 1x or 2x option? That is for you to decide. Technology, research and development don't stand still, and XTR drives the design and principles of Shimano's full mountain bike drivetrain line-up. Everything evolves, whether organically or through the minds and actions of humans- or it dies. If you are a mountain bike rider looking to explore the performance limits of your skill and riding imagination, equipping your current favorite frameset with XTR M9100 components provides the most reliable premium grade platform available. Just remember that the not so humble, incredibly engineered and executed RD-M9100 Rear Derailleur is allowing every pedal stroke to generate power and efficiency, making every shift an afterthought, and maintaining the continual integrity of your drivetrain every second you are riding your bike.