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ShimanoXT FC-M8120 1x Crank Arms


Item # SHIU18B

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  • Black, 165mm ($154.99)
  • Black, 170mm ($154.99)
  • Black, 175mm ($154.99)
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Item # SHIU18B

XT FC-M8120 1x Crank Arms

With single-ring drivetrains effectively taking over the mountain bike world, the quest for more gears quickly led us to 12-speed. Shimano entered the 12-speed realm a little late, but in typical Shimano fashion they took their time to get it right. It started with the race-ready XTR group, but for those of us who don't quite have the funds to reach for XTR, Shimano has trickled that technology down to the XT level. The XT FC-M8120 1x Crank Arms use the familiar hollowcore construction from past years, but now incorporate a user-friendly direct-mount chainring interface, along with a special tooth profile that greatly improves chain retention on these new 12-speed drivetrains.

These M8120 crank arms feature a 55mm chain line and a wider 178mm Q-factor, as opposed to the 52mm chain line and narrower 172mm Q-factor found on the M8100 crank arms. This makes them an ideal choice for burlier all-mountain and enduro bikes that require a bit of extra chainstay clearance. The M8120 cranks are optimized for bikes with 12 x 148mm Boost hub spacing, though both the M8100 and M8120 cranks work with Boost bikes.

The crank arms are constructed using Shimano's proprietary Hollowtech II technology, balancing stiffness, strength, and weight for superior power transfer. Hollowtech uses cold-forging to create a light and hollow crank arm that doesn't compromise on strength or stiffness, enabling you to charge hard into rowdy trail sections without worries of your crankset flexing under pressure or getting damaged by rock strikes. Meanwhile the low weight keeps you from getting bogged down with extra grams when you're pushing for big mile days.

Regardless of your preferred riding style and terrain, you'll appreciate the new direct-mount chainring application. The drive-side arm removes for ring placement, making chainring swaps easy to execute while your crank is still on your bike. This means you can toss on a lofty 34 or 36-tooth ring for smooth rolling singletrack, or give yourself a break with a 28-tooth when climbing is the day's main goal.

  • Workhorse crank arms for Shimano's 12-speed XT drivetrain
  • Hollowtech II construction is lightweight, stiff, and strong
  • Direct-mount chainring interface makes gearing swaps a breeze
  • Q-factor is ideal for bikes needing extra chainstay clearance
  • Chain line is optimized for bikes with 148mm Boost hub spacing
  • Cranks can be easily swapped between 1x and 2x setups
  • Special chainring tooth profile greatly improves chain retention
  • Chainring sold separately

Tech Specs
Arm Materialcold-forged aluminum
Arm Length165mm, 170mm, 175mm
Ringsdirect mount (not included)
BB Type[recommended Pressfit BB] Shimano BB-MT800-PA, [recommended threaded BB] Shimano BB-MT800
Q Factor178mm
Compatible ComponentsShimano CN-M8100 chain, Shimano XT 12-speed drivetrains
Recommended Usemountain biking
Manufacturer Warranty2 years

Actual Weight

Black, 165mm
Black, 170mm
Black, 175mm

Actual weights are measured in-house by the Competitive Cyclist team.

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