Sram Eagle Transmission on an E-MTB: Carefree e-biking with the new Sram gear system?

With the Eagle Transmission, Sram has not simply made some further developments to its popular 1x12 drivetrains. The new design of the rear derailleur in particular is much more than just a small update. The big promise: This derailleur is more robust and durable than any before. What's more, it is designed to function particularly smoothly and with lasting precision. Of particular interest to e-mountain bikers: the shifting performance under full load is said to have improved significantly. Whether in boost or turbo mode, pressing the buttons on the shifters is explicitly permitted at all times and in all riding situations.

The facts about the Sram Eagle Transmission

• New rear derailleur with direct mounting on the frame (full mount), the derailleur hanger is omitted
• Exclusively electronic and wireless (AXS technology)
• New cassette, chain and shifter
• Switching under full load possible
• 1x12 gears
• 520 % bandwidth
• Compatible with all frames designed for UDH
• Simpler setup, permanently accurate function

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Sram Eagle Transmission - the rear derailleur

The biggest innovation is the missing derailleur hanger. Sram calls the mounting on both sides of the dropout "Full Mount". Instead of the often narrow and unstable derailleur hanger, the rear derailleur grips the frame and axle directly with two solid wings. This eliminates tolerances between the XD freewheel, cassette, rear derailleur and rear wheel axle. In addition, the new mounting 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 fall 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. The advantages: shifting inaccuracies due to bent derailleur hangers should be a thing of the past. In addition, adjusting the system has become much simpler. This is because the rear derailleur and cassette are at a precisely standardised distance from each other with the system. This completely eliminates the need for many adjustments to the derailleur. This should completely eliminate malfunctions or inaccurate shifting due to incorrect or misadjusted settings.

Further features of the transmission gearboxes

• 8-10 millimetres slimmer than Eagle AXS and is therefore even closer to the wheel
• Larger friction damper: 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 - Cassette and chain

The cassette is at least as important as the rear derailleur when it comes to shifting performance on an e-bike. Sram has worked intensively on the shifting lanes (climbing aids) and the design of the teeth (Sram calls it X-Sync) for the new transmission cassettes. The result: shifting under full load, even with a massive boost from the e-bike motor, is now possible. We describe in detail below how this is noticeable in riding practice. Also new: Sram has made improvements to the gradation of the sprockets with regard to 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.

For the chains, Sram has adopted the flattop design that is already familiar from the US company's road and gravel drivetrains. However, the same chains are not used for the MTB and e-bike drivetrains as on the road, they only have the eponymous design with the flat top in common. The XO and XX chains are intended for e-mountain bikes. The lightest XX SL version is explicitly not approved for e-bikes. The two E-MTB chains are priced at 120 and 150 euros respectively, which is a real house number for the number one wear part on mountain bikes and e-bikes. Sram has also dispensed with a more robust chain and cassette design for E-MTBs. According to its own statements, pure wear is at a comparable level to its predecessor. With intensive e-bike use, this can be expensive fun. However, it should be mentioned that the high-quality chains and cassettes from Sram performed very well in our last wear test. A different approach Shimano with the robust Linkglide wear parts, which rely on 11 instead of 12 gearsto minimise wear with a wider, heavier and therefore particularly robust design.

Eagle Transmission - the gear lever

The term "shift lever" no longer exists in the transmission universe. Sram calls its new AXS controllers, the wireless shifters for the electronic AXS groupsets, "pods". 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 for e-bikes

Sram offers two different crank versions for Bosch and Brose motors. One carbon (XX: 165, 170 or 175 mm) and one aluminium (XO: 160, 170 or 180 mm). Matching chainrings with a 104 mm bolt circle diameter are available with 34, 36 or 38 teeth. There are also suitable direct mount solutions for Bosch, Shimano and Brose drivetrains, but only with 36 or 38 teeth.

Sram Eagle Transmission in tough e-bike use

Almost six months before the launch, Sram provided us with a Trek Rail with the new Eagle Transmission. Over the past winter, we were able to gain extensive practical experience with the new transmission and see how the system copes with mud and slush.

The very first impression of the new gearstick makes you want more. The ergonomics and operation of the new pods are pleasant and intuitive. Anyone who is used to mechanical shift levers from Shimano or Sram will find their way around straight away. The buttons for changing gears are exactly where you would expect them to be. That was the case with the AXS predecessors from Sram is not always the case. The feedback when pressing the button is also much clearer with the transmission pods. Even when wearing gloves, you can always feel directly whether the switching command has been sent.

Does switching under load also work now?

But what about the gear changes? Of course, you can't expect miracles from a new shifting group. After all, shifting has been absolutely precise and fast for years with all high-quality gearsticks from Shimano and Sram. The Eagle Transmission is no exception. You only notice a difference when shifting under load. This is often the case on e-mountainbikes in particular and is unavoidable on difficult uphills.

With the new Eagle Transmission, you can really press the shift lever in any situation without hesitation. With conventional gears, you literally wince from time to time when the chain hits the next sprocket with a resounding bang. That sounds anything but healthy. These moments no longer occur with the Eagle Transmission. Even with turbo mode engaged and full pedal power, gear changes are relatively smooth. You get the feeling that the chain is being gently placed on the sprocket instead of simply being pushed.

In rare cases, the rider will feel that the gear changes do not take place immediately after pressing the shift lever, but with minimal delay. This is due to the defined shifting lanes of the cassette, which make shifting so smooth. However, this minimal delay was not a disadvantage in any situation in our riding experience. In a very similar way, we have Shimano's new Linkglide technology, which also relies on clearly defined shifting lanes on the cassette sprockets.

Also worth mentioning: In all the months that we rode the Eagle Transmission, we didn't have to make a single small adjustment to the gears. Even at the end of the test period, there was not a hint of chain rattling or jumping gears. In adverse conditions, we found the oversized openings in the lower derailleur pulley to be suboptimal. This is because small botanical debris such as long grasses or small branches occasionally collected here during our test rides.

CONCLUSION from EMTB test manager Florentin Vesenbeckh

Derailleur hangers have always been a nuisance for me, because sooner or later they are easily bent and the shifting can no longer be adjusted perfectly. The approach of the new Sram Eagle Transmission is promising and seems more than logical. I'm curious to see how robust and precise the rear derailleur proves to be in tough continuous use and after harder rock contacts. The smooth shifting performance of the Eagle Transmission under load is particularly exciting for e-mountain bikers. This is next level! However, the new Sram drivetrain is not really the answer to the wear and tear concerns of frequent e-bike riders. The chain and cassette will remain really expensive wearing parts. - EMTB test boss Florentin Vesenbeckh