Sram Eagle Transmission: All information on the new Sram AXS electronic MTB drivetrain
Stefan Loibl
· 21.03.2023
Table of contents
After many rumours about the UDH derailleur hanger and the Prototypes at the 2022 Mountain Bike World Championships in Les Gets Sram lets the cat out of the bag: With its new Eagle Transmission Sram heralds a radical new generation of MTB gears on. Although without a 13th sprocket on the cassette and only as electronic AXS shifting groupsets, but with a fundamentally simplified adjustment process and particularly robust components.
With the largely new Sram AXS generation developed in Schweinfurt the US-Americans are once again putting pressure on market leader Shimano. Because while Shimano more in the direction of e-bike innovations Sram has had a lasting impact on the mountain bike gear shifting market in recent years: After the burial of the front derailleur by 1x11 gears in 2012, Sram pushed ahead with its 1x12 Eagle drives a little later, he was once again in the lead.
With the electronic, wireless Sram AXS drivetrainswhich have been spreading rapidly on high-quality mountain bikes since 2019, the next side blow was aimed at the Japanese. A response from Shimano - in the form of a new generation of Shimano Di2, for example - has been years in coming.
But Sram continues to push ahead and is even going one better for 2023 in the arms race on the MTB drivetrain market: With the three new Sram Eagle Transmission drivetrains, the component giant is talking about the "first gearstick made especially for MTB". Sram product manager Andreas Kölsch, who has been involved in the project for the past five years, calls the next Sram AXS generation the "The most robust MTB gear system ever seen".
Starting signal for new Sram derailleurs as early as 2018 with UDH derailleur hanger
Back in 2018, Sram started its secret gear development programme, which was known internally as the "Top Gun Project". The aim was to eliminate the weak points of the current Eagle drivetrains - such as defective derailleur hangers or incorrectly adjusted and therefore only smoothly functioning gears.
The first thing we tackled was the classic derailleur hanger. These special parts, usually made of aluminium, on the rear, right-hand dropout of the frame are the suspension for the rear derailleur and also serve as a predetermined breaking point to protect the expensive frame and rear derailleur. But it is also a fact that bent derailleur hangers are very often the cause of jittery gearsticks are.
This is why Sram launched its own derailleur hanger (UDH for short) on the market in 2019. Sram did not charge bike manufacturers any licence fees to install the UDH derailleur hanger. This also brought advantages for end customers: A replacement derailleur hanger costs only 10-15 euros and it is easier to get than most derailleur hanger special solutions from bike manufacturers. As a result, the majority of new mountain bike developments since 2019 have relied on UDH as the interface between the frame and rear derailleur.
All too long after its introduction, Sram also picked up the bike developers in 2019 and explained to the manufacturers that the UDH derailleur hanger also embodies the installation standard for the next Sram AXS generation. Over 300 MTB models on the market are now equipped with UDH, meaning that the new Eagle Transmission drivetrains can be used or retrofitted on these bikes.
XX SL, XX and X0: The 3 Sram Eagle Transmission groupsets at a glance
Sram is launching three quality levels and versions of its Eagle Transmission drivetrains for mountain bikers and e-bikers. The XX SL is the most expensive and lightest MTB drivetrain for use on race bikes and light trail bikes. The XX follows in the footsteps of the XX1 Eagle AXS and is also the top groupset for e-mountainbikes.
The new X0 uses a new aluminium crank instead of carbon as the material and is slightly heavier than the XX components, but also cheaper. It is roughly on the same price level as the mechanical XX1 Eagle. All components of these three Sram groupsets can be mixed and matched.
However, it is not compatible with the classic Sram Eagle generation. This is due to the newly introduced T-Type tooth profile, which the chain, chainring, cassette and rear derailleur of the Eagle Transmission have. In addition, the Eagle Transmission requires special wide cranks with a 55 mm chainline.
Comparison of weights and prices of the new Sram Eagle Transmission
We have already weighed all the new Sram Eagle Transmission components. Here are the weights of XX SL, XX and X compared to a Shimano XTR. The prices of the new Sram MTB drivetrains top everything that has gone before. The Sram Eagle Transmisstion is the most expensive groupset in the world.
In terms of weight, however, only the XX SL version is ahead of the much cheaper Shimano XTR. One of the new Sram rear derailleurs alone costs 660-700 euros. For an additional Powermeter crank, which Sram offers with the XX SL and XX, another 300-600 euros are added on top.
It may be some time before the new gear generation is also available at more favourable prices - for example in a GX version. Whether the Eagle Transmission technologies will ever be used on mechanical Sram drivetrains remains to be seen, but is rather unlikely.
Sram XX SL Eagle Transmission
With the lightweight top wireless groupset, Sram saves weight compared to the XX thanks to a carbon derailleur cage, carbon cranks and the omission of the crank bashguards. Hollow rivets in the new SL chain in flattop design save a few grams of weight.
Sram XX Eagle Transmission
In future, the XX and XO will be more clearly separated in terms of price and components. The XX version of the Eagle Transmission remains the top groupset for all types of mountain bikes and e-MTBs. With a total weight of 1726 grams, it is roughly on a par with the Shimano Deore XT.
Sram X0 Eagle Transmission
The X0 version (no longer X01 as in the past) of the Eagle Transmission will be the new Sram groupset that you see most often, as it has the best price-performance ratio. The new aluminium crank of the X0 is an eye-catcher and distinguishing feature. Shaft and crank consist of one part and are milled from an aluminium block. This also makes the MTB crank developed in the USA easy to recycle. The distinctive hole has no influence on the stiffness and reduces the weight. Including the detachable bash guards, the new X0 aluminium crank weighs 684 grams. Individually, it costs 360 euros without the bottom bracket.
Sram Eagle Transmission - the rear derailleur
Sram calls the mounting on both sides of the dropout without a derailleur hanger "Full Mount". This eliminates tolerances between the XD freehub, cassette, rear derailleur and rear wheel axle. In addition, the new derailleur hanger attachment creates a much stronger connection, as it grips on both sides of the frame and the rear derailleur is supported by the axle and frame.
Many people will ask themselves: What about the predetermined breaking point function of the classic derailleur hanger? Is the frame broken if I crash with Eagle Transmission? No, because the new Sram AXS rear derailleur is connected to the axle system and designed to be extremely robust. According to Sram, total derailleur damage or breakage should be a thing of the past.
Set-up instructions via app instead of adjusting by feel using screws
Another innovation that you won't find on the new Sram Eagle Transmission rear derailleur is the adjustment screws. The two limit screws are superfluous, as the rear derailleur located under the cassette is always positioned to match the sprocket set anyway. To ensure even easier gear adjustment for every mountain biker, Sram has also removed the adjustment screw for chain gap adjustment (B gap screw). With current Sram derailleurs, this requires the Chain Gap Tool and had to find the correct B-gap setting for fullys in the SAG - which required two people. With the new Eagle Transmission, on the other hand, there are only two positions (A or B) on the rear derailleur. Via the so-called "Setup Key" or the AXS app, Sram provides specific chain gap recommendations for each bike model and frame size as to whether the screw should be set to A or B. Sram also specifies the appropriate chain length via the app with the exact number of links, so there is no need to cut the chain to length by eye. All in all, Sram significantly simplifies the adjustment process for the Eagle Transmission in order to eliminate potential sources of error. But hobby mechanics beware: the assembly and adjustment process is fundamentally different to that of current Shimano or Sram derailleurs.
Further features of the Sram transmission rear derailleurs
- 8-10 millimetres slimmer than Eagle AXS and is therefore even closer to the wheel
- Larger friction damper with more tensioning force for the chain
- Overload clutch as protection in the event of rock contact or falls (overload clutch)
- Lower shifting wheel continues to rotate when a stick gets stuck (Magic Wheel)
- 14 instead of 25 levels for fine adjustment (Micro Adjust)
- Replaceable covers on the rear derailleur in the event of damage/scratches (skid plates)
- Cage and rear derailleur body can be separated without tools
- Cage can be retrofitted individually
Eagle Transmission - the cassette
Sram has made improvements to the gradation of the sprockets in the jumps of the large sprockets. The Eagle Transmission cassettes with 10-52 teeth have a gear range of 520%, continue to rely on the proven XD freehub and offer an improved gear gradation with 38 and 44 teeth in the mountain gear range (compared to the 10-52 cassette of the classic Eagle drivetrain). This should make the jumps more homogeneous when riding uphill. With the new cassette, Sram comes very close to the gradation of Shimano, whereby Shimano "only" goes up to a maximum of 51 teeth. Sram has also worked intensively on the shifting lanes (climbing aids) and the design of the teeth (Sram calls it X-Sync) for the new cassettes. The result: shifting under full load in both directions is now possible! During our test rides, we were amazed ourselves that you can really operate the shift lever at any time without hesitation and that the chain unerringly finds its way to the next sprocket. In some cases, shifting is not performed immediately after pressing the thumb, which is why it feels a little delayed in some situations. On the other hand, you can shift gears without hesitation even when pedalling out of the saddle and at high torque.
What is the red plastic ring in the cassette for?
To save weight, the second and third sprockets are now made of aluminium and pinned to the cassette body. The red plastic ring on all Eagle Transmission cassettes marks the seventh gear, which is also the adjustment sprocket for the setup. Sram chooses a centre sprocket, as this means that the chain gap setting fits better across the entire cassette. Sram is setting new standards in terms of price: the cassettes cost between 480 and 720 euros individually as retrofit components.
Eagle Transmission - the chain
For the chains, Sram has adopted the flattop design already familiar from the US company's road and gravel drivetrains. However, the same chains are not used in the MTB drivetrains as on the road, they only have the eponymous design with a flat top in common. Recesses on the outer plates reduce the weight so that an XX SL chain of the Eagle Transmission (126 links) weighs only 265 grams including chain lock. Thanks to the new T-Type design, the chains can only be used with the Transmission drivetrains. The lightest XX SL version may not be used on e-bikes, whereas the XO and XX chains are also approved for e-MTBs. The new Sram chains are priced between 120 and 180 euros, which is a real house number for the number one wear part on a mountain bike.
Eagle Transmission - the AXS controller
With its new MTB drivetrains, Sram is also launching new AXS controllers - wireless shifters for the electronic AXS groupsets. The new AXS pods are smaller and lighter than all previous AXS controllers for MTB. The Ultimate AXS Pod, including the new Infinity handlebar clamp, weighs just 46 grams. Sram has also improved the ergonomics: you now get clearer, haptic feedback when you press the shift button. The AXS pods can also be adjusted much more flexibly depending on the fittings and handlebar shape. Thanks to the new Infinity handlebar clamp, they can be infinitely adjusted and used with one and the same clamp on both sides. The AXS Pod is powered by a CR2032 button cell and is dust and waterproof. The Ultimate version of the new AXS Pods can also be customised with convex and concave buttons. The new Sram AXS shifters can be customised in the same way as the previous AXS controllers and can also be retrofitted to old AXS shifters. Price: 180-240 euros depending on the version.
Eagle Transmission - the cranks
The XX SL and the new XX use the same hollow-core carbon cranks as the previous Sram Eagle groupsets. Only the aluminium crank of the X0 is a completely new development. The chainrings with the new T-Type tooth profile are new and ensure that the crank cannot be mixed with old Sram Eagle 12-speed drivetrains. There are also special cranks for E-MTBs from the XX and X0 Eagle Transmission. The eye-catchers of the new Sram cranks are the two removable and replaceable bashguards. The XX SL crank does without this additional weight. All three new MTB cranks can be retrofitted with a power meter.
Interview with Sram engineer Frank Schmidt
BIKE: Why can mountain bikes do without a derailleur hanger in the future?
Frank Schmidt: Well, because there are now derailleurs that are attached directly to the frame. This eliminates all the tolerances that are currently on the market in the frame and derailleur hanger. The rear derailleur is positioned directly in relation to the cassette, which has many advantages.
BIKE: You're not talking about a new standard, which isn't the case either. But nevertheless, with UDH you are presenting something new that is needed to ride the Eagle Transmission. Are you open about this frame interface? Are you open to other gear manufacturers perhaps being able to use this connection in the future?
In principle, we are open up to a certain point. We have of course secured our technology in terms of patents. We don't want it to be copied immediately. But other solutions that utilise this standard are definitely possible. And it is still possible to fit a UDH derailleur hanger in order to use traditional systems.
BIKE: So the development of the last few years has been: 2x10, 1x11 and then 1x12. But now the Eagle Transmission is not moving towards 1x13, but more towards robustness. Does this mean that the 1x13 drivetrain has been written off or has it just been postponed and can come in a next step at some point?
We decided against implementing a 1x13 system. 13 gears would have made everything wider again, would have made the gaps thinner and would probably have made adjustability more critical. A 13-speed MTB drivetrain would therefore have meant many compromises. And we didn't see the benefit of where this one gear could actually have been placed. You could have made an even bigger sprocket, but our data shows that nobody actually needs that. The spread that is available is sufficient for 99% of riders. In this respect, we decided to focus on robustness and make the system simpler and easier to adjust.
BIKE: On the subject of robustness: Despite all the robustness, a chain and a cassette are still wearing parts, which doesn't change anything. Are the new Eagle Transmission drivetrains more durable than what we've seen so far?
In terms of wear, the new Eagle Transmission is on a similar level to the previous Eagle drivetrains, which are already very durable. In some areas, it is even slightly more durable, but this depends heavily on the individual area of use and maintenance.
BIKE: You have partially eliminated or massively simplified the adjustment process for the Eagle Transmission. Was that really something you found to be a problem, why gears don't work outside?
Definitely! With previous systems, the chain gap, i.e. the wrap, should be set in the SAG. This is difficult for many to implement and therefore a major source of error. There are also often misunderstandings, with many bikers believing that the screw is used to adjust the chain tension or something similar. As a developer, you are constantly surrounded by experts, but you can't expect that in practice later on.
BIKE: In the past, you could mix and match shifting components on an MTB. For example, with 2x10, 3x10 or 11-speed drivetrains, bikers could sometimes combine components from different gear manufacturers or third-party suppliers. Are the days of the Eagle Transmission finally over?
We have consistently developed the Eagle Transmission as a complete system. It is quite possible that other manufacturers will develop compatible cranks or chains in the future, but the new drives are not compatible with existing parts. For maximum system performance, the individual components must be developed together and harmonised with each other.
BIKE: The Eagle Transmission will certainly be found in large numbers as a groupset on new bikes in the near future. But what about retrofitting? Does it even work? If so, what does my bike need so that I can retrofit it?
Essentially just the UDH. Unscrew the old groupset and fit the new system. You don't need a new hub, even if the cassette moves slightly outwards. The Eagle Transmission can be fitted to all mountain bikes with Boost and UDH.
BIKE: Recycling and reparability. How important was this in the development process and in which parts was it specifically incorporated?
This topic is becoming increasingly important to our development team. For example, the X0 crank is now made of aluminium instead of carbon. The crank and axle also consist of one part, which means that it can be recycled separately. In practice, this is usually still a challenge, but we are working on it. Some parts of the rear derailleur, such as the outer links, can now be replaced if they have been scratched or otherwise damaged in crashes. We have so-called skid plates that provide additional protection for the main components. These can be easily replaced and recycled. And finally, the rear derailleur can also be completely dismantled in the event of a total loss to enable relatively pure recycling.
BIKE: And what's more, only the cage of the Eagle Transmission rear derailleur can be replaced, right?
Exactly, that is also an innovation. The main derailleur with the parallelogram is definitely extremely robust. What you can't completely rule out is the possibility of the cage being bent by sticks in the spokes or falls. If this happens, the entire cage unit can be replaced very easily and even without tools.
BIKE: It's amazing how much expertise and detail has gone into the cassette. How much development has gone into it and is the cassette ultimately the part of the Eagle Transmission that is decisive for its function?
The Eagle Transmission rear derailleur is certainly the eye-catcher of the whole system and attracts the most attention. But ultimately, the rear derailleur simply moves to a new position. How well it shifts essentially depends on the design of the cassette and the interaction with the chain. A great deal of effort has been put into this and a lot of detailed work has gone into it. That's why the cassette is extremely important for shifting performance.
