SRAM S100 Eagle B1 12-Speed Long Cage 50t Max Black Rear Derailleur

The SRAM S100 Eagle B1 is a cable-actuated 12-speed Eagle derailleur for 11-50t and 10-50t cassettes, built for high-torque use including e-bikes and everyday trail riding. SRAM based it on ten years of Eagle development and revised the bushing fit for long-term precision.

It mounts to a traditional derailleur hanger, or to a UDH with SRAM's Half Mount plate for extra security (UDH and plate sold separately). It is backward compatible with the Eagle SX, NX, GX, X01 and XX1 ecosystem, but not with Eagle 70, Eagle 90 or Eagle Transmission.

Who It's For

• Riders replacing an SX or NX Eagle derailleur on a 50t cassette.
• Bike builders who want a durable 12-speed derailleur that can be Half Mounted on a UDH frame.
• Consider a different derailleur for 52t cassettes or T-Type Transmission drivetrains.

What to Look For

• Ecosystem: Works with Eagle (non-T-Type) shifters, cassettes and chains. Not compatible with Eagle 70/90 or Transmission.
• Cassette: 11-50t or 10-50t; 50t maximum cog, 40t capacity.
• Mount: Traditional hanger, or UDH plus Half Mount plate (sold separately).

Key Features

Drag Spring cage damper. A friction spring damper that holds chain tension for chain retention on rough terrain.

Half Mount ready. The mounting bolt accepts SRAM's Half Mount plate when used with a UDH, which SRAM says increases hanger security.

Improved bushings. A revised bushing fitment process aimed at long-term durability and shifting precision.

500% range. Long cage sized for a 50t cassette.

Rider Intent Summary

• Biggest strengths: Durable 12-speed Eagle shifting with a Half Mount option.
• Tradeoffs: 50t max; not Transmission-compatible.
• What makes it different: A modernized entry Eagle derailleur that can borrow some UDH security without a T-Type frame setup.

Victory's Take

We like the S100 as a tough replacement derailleur for e-bikes and entry trail bikes. Victory Bicycle Studio can tell you whether Half Mount suits your frame.

Specifications

• Brand: SRAM
• Model: S100 Eagle (B1)
• Drivetrain speeds: 12
• Largest cog: 50t
• Chain wrap capacity: 40t
• Cage length: Long
• Mount: Traditional hanger or UDH with Half Mount plate (sold separately)
• Shifter compatibility: SRAM X-Actuation (Eagle)
• Damper: Drag Spring
• Not compatible with: Eagle 70, Eagle 90, Eagle Transmission
• Color: Black
• Part number: 00.7518.205.000