Sram's new Eagle Transmission is here. Radically different from previous generations of Eagle 12 speed drivetrain, Eagle Transmission promises better durability, reliability, and shift quality. Compatible with all Sram UDH-equipped bikes, Eagle Transmission replaces the traditional derailleur hanger entirely for a stiffer, stronger and totally rebuildable direct-mount derailleur system.
What Do I Need to Know?
Sram's Eagle Transmission is the biggest revision to the modern derailleur system in years. Doing away with the derailleur hanger, it moves that failure point elsewhere on the derailleur itself, building in safety mechanisms that should result in fewer failures while also building the derailleur on an architecture that allows for the derailleur to be fully rebuilt.
For anyone looking to upgrade their drivetrain to the new Eagle Transmission, it is important to know that it is only compatible with UDH-equipped bikes. If you're not sure whether your bike is UDH-equipped, check the list here or look up the specs of your bike on the manufacturer's website. Fortunately most major brands are now UDH-equipped. Eagle Transmission is also designed as a complete system, meaning that it is not cross-compatible with other Eagle components and should only be used with other T-Type components - so XO, XX or XX SL.
What Does It Do Differently?
The Eagle Transmission sets out to do things completely differently from the outset. Eliminating the derailleur hanger means a much stiffer derailleur that shrugs-off shift-affecting impacts with ease. Of course this force has to go somewhere, which is why Sram have designed the derailleur to pivot around the mounting bolt to move out of the way under impact. This can be easily reset simply by moving it back by hand or loosening and tightening the axle. The new derailleurs are also fully rebuildable; more on that below. Since the derailleur is centered on the rear axle without a hanger to bend, this means perfect shifting every time. The way that the derailleur mounts directly to the frame also means that it can be much lower profile and therefore should be less prone to impact in the first place, being tucked further from harm's way.
Taking the human error out of setup is another main selling-feature for Eagle Transmission. Fully electronically controlled and with no external adjustments, the new transmission indexes itself based off the geometry of the mounting bolt and the red setup cog on the cassette. Setup is achieved using the AXS app and using their chain length calculator, accounting for geometry and suspension kinematics, supplies optimal chain length and the "A" or "B" position of the Setup Key. All of this means an optimal setup with zero guesswork.
Completely redesigned chain and cassette means improved shifting. The chain resembles the flat-top road chains but should not be mistaken - the Eagle chain is different, no doubt accounting for more extreme operation conditions and chainlines. New and improved shift ramps on the cassette mean smoother shifting, especially under load; an important consideration given the large market segment that ebikes now make up. The cassettes also have revised ratios, making for more natural feeling steps between sprockets, notably the jump between the two easiest gears now being 44-52t rather than 42-52t.
We Can Rebuild
This new generation of AXS is now fully rebuildable. Older generations of AXS had a small number of spare parts available, namely the inner cage and pulley wheels. Despite the protection mechanisms built into the new derailleurs, impacts are inevitable and Sram know that it's important to be able to rebuild a derailleur when they cost around $1000 each. For this reason, many of the parts on the new derailleurs are designed to be replaced and will be readily available. The parallelogram and upper part are designed with a built-in skid plate that can be replaced for tens of dollars rather than hundreds.
The entire cage and clutch assembly is easily removed and refitted in a handful of seconds and is cross-compatible across XO, XX and XX-SL. Pulley wheels are available separately, as are the cage lock and the derailleur mount. The lower pulley wheel also features a 'magic wheel' breakaway design where the teeth can rotate around the wheel itself if a stick gets caught in there, thus preventing further damage to the cage and other components. The new chainrings feature two integrated and removable/replaceable bash guards that come preinstalled and can be configured for either foot-forward, or not at all and should ward off all but the biggest impacts.
More Ergonomic, More Better
Along with the new drivetrain comes a new shifter, designed to be simpler; because simpler is usually better. The new shifter uses a more ergonomic mount that's super-slim and enables it to be positioned almost anywhere on the handlebar. The stock mount can be flipped for the shifter to run in either direction, inside or outside of the brake and can be positioned back and forth and also allows for the shifter to be rotated, allowing perfect positioning. It can also be positioned on the other side of the bar to control an AXS Reverb dropper post. There is also a new matchmaker version of the mount available for those that want fewer mounting points on their bars, though it doesn't offer quite the same level of customisation. The new shifter itself uses a two-button arrangement that, while almost too simple looking is extremely intuitive to use.
Spec level
Spec starts at the X0 level, designed to directly replace the X01 Eagle AXS derailleur, though as a complete ecosystem with new cassette, chain, derailleur, cranks, and shifter. The X0 spec comes with an aluminum crank with a unique hollowed-out design and a machined finish that should wear well with minimal chance of heel-rub making it look untidy. The cassette is mostly steel with the largest three sprockets made of aluminum to save weight and riveted together. X0 is, as always, the workhorse groupset designed to go anywhere, do anything and provide amazing, reliable shifting.
Moving up to XX level gets a carbon crank with foam core similar in look to previous cranks but with more subtle graphics, a lighter CNC-machined chainring and bash guard. The derailleur is a little lighter with more CNC'd parts and a polished alloy cage rather than black and the cassette again has more machining with a silver finish that should wear well. The chain again has a silver finish and has hollow pins for weight saving. There is also a power meter version of the XX crank with the power meter neatly housed in the crank spindle. XX is the lightweight yet robust groupset for those that must have the best there is, designed to withstand the rigours of trail and enduro riding.
New for this generation of AXS is the flagship XX SL group that saves even more weight from the already svelte XX groupset. The crank is a hollow carbon construction with a lightweight extensively machined chainring and does not come with a bash guard. The chain features hollow pins and plates for extreme weight savings. The derailleur is similar to the XX version but this time has a carbon cage for strength and even more weight saving. The cassette features more machining and is Sram's lightest 10-52t cassette to date. Again there is a power meter and non-power meter version of this groupset. XX SL is the lightweight cross country race groupset prioritizing weight and efficiency.
All groupsets come with everything needed except bottom bracket and can also be purchased as separate items. The cranks all use the existing DUB standard and cassettes the XD standard, with the derailleur being the only part that requires any special or new in the UDH mounting standard. The only cassette option currently is 10-52t and chainrings can be had from 30-38t. Chainrings come in a direct mount pattern and there are also e-bike specific cranks for Bosch and Brose, as well as chainrings for Bosh, Brose, Shimano and 104BCD cranks. Set up requires no proprietary tools and nothing that the competent mechanic should not already have. For extensive and detailed setup guides and more check out the Sram website.
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