SRAM Eagle & Eagle Transmission MTB Reference: XX1 · X01 · GX · NX · T-Type

/ 01

Eagle vs Eagle Transmission — what's the difference?

/ 02

Eagle tiers — from XX1 to SX

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Eagle Transmission tiers — XX SL to GX T-Type

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Cassettes — XD vs HG vs splined

Eagle XD cassettes (XX1/X01/GX) thread onto an XD driver freehub — one-piece machined steel, light and stiff. The 10-52T range delivers 520% across all current tiers; the 10T start sprocket is the defining Eagle trait.

NX and SX Eagle cassettes use a standard HG spline freehub (the one that's been on mountain bikes since the 90s). This is deliberate: NX lets you bolt a 12-speed drivetrain onto old wheels without changing the freehub. The trade-off is the 11T top sprocket (not 10T) and roughly 200 g heavier than GX.

T-Type cassettes use a new splined interface: the cassette slides onto a splined freehub body and is secured by a single lockring — no threading, no cassette tool for removal. The alignment is more precise and the system is stronger under the high shift loads Transmission generates.

/ 05

Chains — FLATTOP engineering

All Eagle 12-speed chains use SRAM's FLATTOP profile (the top plate is flat — no traditional roller). This gives the chain a harder surface for the cassette's shifting ramps and reduces noise. Eagle chains are NOT cross-compatible with Shimano 12-speed (which uses HYPERGLIDE+ with a different roller profile).

The T-Type chain (CN-TTYP-XX1, ≈240 g) has been redesigned with a stiffer outer plate for the harder shift loads under power. T-Type chains work on Eagle cassettes; Eagle chains do NOT work on T-Type cassettes — the inner width is different. T-Type chains are available in XX SL (lightest, hollow pins), XX, X0, and GX grades.

Chain wear tool: use a 12-speed-specific checker (SRAM's TL-CHCK12 or Park CC-4). Replace at 0.5% elongation. A worn chain on an XG-1299 cassette is an expensive mistake — the cassette costs more than 6 chains.

/ 06

UDH — the frame interface that makes T-Type possible

The Universal Derailleur Hanger (UDH) is SRAM's open-standard frame interface, launched in 2019 and now adopted by nearly every major MTB frame brand (Specialized, Trek, Giant, Santa Cruz, Yeti, etc.). A UDH frame has a standardized threaded insert at the dropout — if you hit a rock and break the hanger, any shop has a replacement for ≈$15.

Transmission takes UDH further: the derailleur bolts directly into the UDH mount, eliminating the separate hanger entirely. This is why T-Type has no B-gap adjustment or limit screws — the derailleur's position relative to the cassette is fixed by the frame geometry, and the setup app (AXS app) handles the rest. You literally bolt it on, pair it, and ride.

Frame check: if your frame has a replaceable derailleur hanger held by a single bolt through the dropout, it's probably UDH. Look for two M3×0.5 threaded holes flanking the dropout bolt — those are the UDH mounting points. Non-UDH frames cannot run T-Type.

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AXS setup — app-based, no cables

All Eagle AXS and T-Type derailleurs are set up via the SRAM AXS app (iOS/Android). The app guides you through pairing shifters, setting the chain length, and micro-adjusting the indexing in 0.25 mm increments. For T-Type, the app also runs a 'setup key' calibration that confirms the derailleur is in the correct UDH position.

AXS batteries (same across road and MTB) last ≈20 hours of ride time and swap between derailleur and shifter in seconds. One spare battery covers both — if your RD battery dies, borrow the shifter battery to get home (the shifter battery lasts months).

The AXS Pod shifter (MMX clamp, two-button 'rocker') is the standard shifter for both Eagle AXS and T-Type. The Pod Ultimate adds a textured thumb pad; the Pod (base model) is the same internals in a simpler housing. Both are fully wireless and pair via the AXS app.

/ 08

Eagle mechanical — cable-actuated, still relevant

For builds where battery management isn't wanted or budget is the priority, mechanical Eagle (GX, NX, SX) still works well. The GX mechanical shifter (GX Eagle, MMX clamp) has a positive, clunky detent that's become the reference for MTB shift feel. Cable routing is standard — full housing from shifter to derailleur, no housing stops.

Mechanical Eagle derailleurs use SRAM's Cage Lock: push the cage forward and press a button to lock it open for wheel removal — no fighting the clutch spring. The NX derailleur (≈325 g) is the workhorse; the SX derailleur (≈345 g) is heavier but costs half as much. Both have the same clutch and pulley design as GX.

/ 09

Which Eagle / Transmission to pick

GX Eagle (AXS or mechanical): the value reference point. GX AXS gives you wireless electronic shifting for roughly 2/3 the cost of X01 AXS with the same shift quality. GX mechanical is the standard for OEM builds at the $3,000–5,000 price point.

X01 Eagle / X0 Transmission: the enthusiast's pick. Lighter cassettes, carbon cranks, and (on T-Type) the Setup Key calibration and stronger shift motor. If you race enduro or ride 100+ days a year, the weight savings and durability justify the premium.

NX Eagle: the upgrade path for an older bike with HG wheels. NX gives you 12-speed range without swapping wheels, and the derailleur is the same design as GX. The PG-1230 cassette is heavy but durable. Best value upgrade for a 2018–2021 bike.

GX Transmission: the entry point to T-Type. The derailleur is heavier than X0 but shifts identically — same motor, same shift speed, same setup. The GX T-Type cassette (GX-1275-T1) is the same 10-52T range as XX SL but at roughly 1/3 the price. For most riders, this is the T-Type to buy.

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Shimano Hyperglide+ comparison — the Eagle competitor

Shimano's Deore XT M8100 and XTR M9100 (12-speed, HYPERGLIDE+) are the direct competitors to Eagle. The key difference: Shimano cassettes use MICRO SPLINE freehubs (not XD or HG), and Shimano's shift ramps prioritize smooth downshifts under power (RAPIDFIRE PLUS). SRAM's shift feel is more positive and mechanical; Shimano's is lighter and smoother — a preference choice.

Shimano has no direct answer to T-Type: XTR Di2 (M9150) is wireless but still uses a derailleur hanger and B-gap adjustment. T-Type's UHD direct-mount advantage is unique to SRAM for now. Shimano's expected Di2 MTB update (rumored for 2025–26) will likely adopt a similar direct-mount approach.

Freehub compatibility table (what fits on which wheel): XD driver → Eagle XX1/X01/GX cassettes only. MICRO SPLINE → Shimano 12-speed cassettes only. HG spline → Eagle NX/SX, older Shimano 11-speed, and any 8/9/10-speed cassette.