Find Your Store
Home Page

Cart, contains 0 items

When autocomplete results are available use up and down arrows to review and enter to select. Touch device users, explore by touch or with swipe gestures.
Expert Help
Earn Rewards

XT RD-M8100 Rear Derailleur

5 out of 5 stars
1 Review
Current price: $103.69 Original price: $121.99
15% off

Style & Size:


Why We Like The XT RD-M8100 Rear Derailleur

It's been a little while since we've seen an update to Shimano's coveted XT group. In fact, the last time we saw big changes was when things shifted to 11-speed, which should make it no shock at all that Shimano's new XT RD-M8100 Rear Derailleur comes along with the launch of 12-speed XT. The new derailleur packs in a new, larger 13-tooth pulley, and carries on with the proven Shadow RD+ low-profile tech that keeps things tucked out of harm's way when the trail gets loose, wily, and filled with menacing boulders hungry to take a bite out of bike components.

The new derailleur comes in two versions, the M8100 and M8120. This particular model is built for one-by drivetrains, to be paired up with Shimano's new 12-speed cassette. It's capable of running both the 10-45t and 10-51t cassette, but won't fair well if you're hoping to run a two-by crank setup. The derailleur brings a new level of silence to the drivetrain thanks to decreased tension in the lower gear positions, plus an added bumper on the pulley cage. The shifting is a bit faster than on the 8000-series derailleur thanks in part to the larger pulley.

One thing that we're thankful has stayed the same through the generations is the stabilizer switch that we saw trickling down from XTR in the previous model. When engaged, this switch helps to eliminate chain slap and dropped chains by increasing spring tension. This is a valuable option for suspension systems that require chainstays and pivots located close to the rear derailleur. The RD M8100 keeps a good thing going with some of the previous model's improvements, including the direct cable path. Your shift housing can enter the stop on the derailleur without the traditional loop of excess housing that often was the victim of contamination in yester-years.

Shimano sticks with the old-reliable aluminum components in the XT derailleur. All of the linkage plates, knuckles, and cage sides are made from it, so while it may lack the carbon-fiber-laden aesthetic of the XTR line, it's more affordable, and if you're been running XT derailleurs as long as most of us around the office have, you know you'll get plenty of mileage out of it.


  • Shimano's workhorse rear derailleur goes 12-speed
  • Shadow RD+ with stabilizer switch reduces chain slap, chain drops
  • Lofty cage length is compatible with both of Shimano's 12-speed cassettes
  • Decreased tension at low gear keeps things smooth and quiet
  • New bumper on pulley cage reduces noise
  • Fast and precise shifting performance optimized for trail riding
  • Durable aluminum construction holds up to trail abuse
  • Compatible with 1-by-12 groupset, for 2-by applications reach for the RD-M8120
  • Item #SHIU18I
(GS) 35t [SGS] 41t
Cassette Range
[GS] 10-45t, [SGS] 10-51t
1 x 12
Shimano 12-speed
Claimed Weight
10oz (287g)
Manufacturer Warranty
2 years
mountain biking

Overall Rating

5 based on 1 ratings

Review Summary

1 Stars - 0 reviews
2 Stars - 0 reviews
3 Stars - 0 reviews
4 Stars - 0 reviews
5 Stars - 1 reviews

What do you think about this product?


Selecting an option will reload the available reviews on the page
5 out of 5 stars

March 24, 2023


GS = 1x12sp with a 45t max cog in cassette SGS = 1x12s with a 51t max cog in cassette

Tyler T

Originally reviewed on