When SRAM introduced its Eagle Transmission drivetrains, it marked a significant step in the evolution of mountain bike drivetrains. Shift smoothness under power and ease of setup were significantly improved, but shift speed, cost, and adding more batteries to the bike were deal breakers for some.
SRAM fills the void with its new Eagle 70 and 90 Transmission drivetrains, which deliver a more affordable mechanical version with much of the same technology that makes the electronic models great. We tested the Eagle 90 Transmission group to see how it stacks up against the rest.
Tech features:
Like SRAM’s electronic Transmission drivetrains, the Eagle 90 (and 70) is centered around a new direct-mount interface that eliminates the traditional derailleur hanger. The derailleur bolts directly to the frame’s Universal Derailleur Hanger (UDH) mount, designed to increase rigidity and shifting precision.
It is also fully rebuildable with most parts available separately in case something bad should happen to it. Replacement parts include the cage assembly, mounting bolt, and frame sleeves, cover/skid plates, B-knuckle, pulley wheel assembly, setup key/cage lock, inner and outer links, bushings, and the P-knuckle, making it the most rebuildable derailleur in SRAM’s Transmission lineup.
SRAM also offers a GX Eagle AXS Transmission upgrade kit that includes an AXS-enabled derailleur body, AXS battery, and AXS pod controller for those wanting to take the Eagle 90 to the wireless electronic GX AXS level.
Shifting is handled mechanically via an all-new textured aluminum paddle-style shifter mechanism. The Eagle 90 shift lever features stealth architecture and MMX compatibility for clean mounting with SRAM brakes. The system utilizes SRAM’s existing GX level 10–52T cassette and a flat-top chain that is specifically shaped to reduce noise and improve durability. The forged-aluminum cranks are compatible with 8-bolt T-type chainrings and are available in lengths ranging from 155mm to 175mm in 5mm increments. Its chainring is a silver stamped-steel T-type with optional bash guards.
The drivetrain is designed exclusively for use with UDH-compatible frames and operates as a complete system; mixing components from earlier Eagle generations is not supported. However, one can mix and match Transmission components to create a lighter, more affordable, or color-matched setup.
Field test results:
SRAM claims that its T-type mechanical drivetrains are the easiest to set up mechanical systems ever offered, and we have to agree with them. It’s as simple as entering your bike’s information in the online setup guide page or in the AXS app to find the derailleur’s setup key, setup cog and chain length. Then you install the components, set the derailleur’s position and adjust cable tension. There are no high or low derailleur stops to adjust or B-tension screws.
Between our test group and Eagle 90 Transmission drivetrains on various test bikes, we have logged a lot of miles on the new components. Test riders love the seamless feel of shifts even under full power, and even on eMTBs. Shift smoothness under high loads is class-leading.
They also appreciate the shift speed that it delivers compared to its sluggish electronic family members. Shift speed is way faster across both directions of the cassette. However, it comes at a slight cost in shift cleanliness. Between the mechanical human factor of a finger pushing a button or lever and the increased speed of the shifts, they are, at times, crunchier than the consistently seamless feel of the electronic versions.
Shift-lever feel is on the cheap side, but not tragically so. Still, they do not have the tight high-quality feel of Shimano’s high-end offerings or Vivo’s F3.
Like other Transmission derailleurs, the Eagle 90 withstands some pretty big hits and comes away with nothing more than a few scratches. We never damaged anything to the point of needing to rebuild the derailleur; however, we like that it’s rebuildable and you can buy parts instead of being forced to buy a whole new derailleur.
Weight-wise, the mechanical Eagle Transmission is 23 grams lighter than the GX AXS Transmission for the shifter and derailleur, but 89 grams heavier at the cranks because of the steel chainring. And, it’s a bit heavier than the previous GX-level mechanical Eagle drivetrain. Still, for most, the ease of setup, smoothness of shifting under power, and ability to rebuild and upgrade will be worth it.
HITS:
• Smooth shifts under power
• Easy setup
• Affordable
• Rebuildable
MISSES:
• Not the lightest
STAR RATING: ★★★★½
Weight: Derailleur, 389 grams; shifter, 142 grams (w/ cable and bar clamp); crank, 812 grams (165mm w/ guards); bottom bracket, 76 grams (threaded); cassette, 446 grams; chain, 284 grams
Price: $735
Contact: www.sram.com