SRAM is entering the market for motor and e-drive manufacturers – this rumour has surfaced regularly in recent years. In the 2023 World Cup season was the Gasgas-Sram Racing Team centred on the German racer Johannes Fischbach Prototypes of the SRAM system are already on the road. But exactly what lies behind them has remained a secret from the public until now. We can now reveal all the details about the SRAM Eagle Powertrain.
First of all: SRAM has not developed its own motor from scratch, but is instead using hardware from Brose. What’s new about the Eagle Powertrain is the complete system and, above all, its integration and combination with the Eagle Transmission gear system. As with Shimano’s EP801 and the new Shimano XT Di2 So now SRAM is also integrating the motor with the gear system. The result and standout feature of the SRAM drivetrain: automatic gear-changing functions. Similar features are also available on the Pinion’s combined motor-gearbox unit (MGU) and Shimano’s new Di2 groupsets.
Table of Contents
- The SRAM motor
- All the facts about the Eagle Powertrain
- The SRAM batteries
- Pods and display: Powertrain controls
- Eagle Transmission and the automatic gearbox
- The AXS app
- The bikes with the Eagle Powertrain
- Review: Eagle Powertrain and the automatic gearbox
- Conclusion, pros and cons
- Interview: What Sram has to say
The engine
For the motor, SRAM uses tried-and-tested hardware from the Berlin-based motor specialist Brose. The basis is the Drive SMag, which runs the SRAM motor using its own software. Even though this motor has been around for a few years now, it is still one of the most powerful and, above all, quietest classic e-MTB motors on the market. Not least in the hugely popular Specialized Turbo Levo, it has a large fan base.
Weighing in at just over three kilos, it isn’t one of the very lightest e-drives, but it’s only slightly heavier than Bosch’s Performance CX. What’s more, at 90 Newton metres, it delivers more torque than its rivals from Bosch, Shimano and Yamaha (85 Nm each). Another advantage over the competition is that the Brose is quiet even on downhill sections; there’s no rattling to disturb your ride.
Special feature: The SRAM motor has just two assistance levels, named ‘Range’ and ‘Rally’. The idea behind this is to keep the operating logic as simple as possible. To ensure everyone can manage with just two levels, the modes can be fine-tuned using two parameters. This is done via the app, where the two parameters for each mode – maximum power and assistance (how hard do I need to pedal to get full power) – can be adjusted using a slider.
This allows you to create a power-saving mode for flat sections or when heading to and from the trail. And a high-performance mode for steep climbs and uphill challenges. Why this minimalist approach? It means a single button is all it takes to switch back and forth between the two modes. And a simple operating system with a clean cockpit layout was particularly important to the developers – but more on that later.
The facts about the SRAM Eagle powertrain
- A complete system comprising a motor, battery, controls and SRAM Eagle Transmission gears
- Automatic gear-changing functions available (Auto-Shift and Coast-Shift)
- Two battery options: 630 or 720 watt-hours
- Option for a range extender on the down tube (250 Wh)
- The motor utilises hardware from the Brose Drive SMag (90 Nm maximum torque)
- Two support levels: “Range” and “Rally” (both adjustable via the app)
- Fully wireless control via four buttons on the handlebars for all gear-change and engine functions
The batteries in the SRAM Eagle powertrain
The Sram drive system works exclusively with the company’s own specially developed batteries. There are two variants to choose from: 630 watt-hours for a classic and convenient flip-out design, or 720 watt-hours for fixed integration or as a slide-in solution. At 3.1 kilos, the smaller version is very light considering its capacity. The larger 720-wh version weighs 4.1 kilos. Both batteries utilise modern 21700 cells.
In addition, SRAM has developed a range extender. This allows an extra 250 watt-hours to be housed in the frame triangle. However, unlike some rival products, the compact battery does not fit into a standard bottle cage. A separate, robust mount – which, according to SRAM, is completely rattle-free – is attached to the bottle cage bolts. An adapter plate for a bottle cage can also be clicked into place here, allowing you to switch easily between water bottle and range extender modes. The additional battery is connected to the Powertrain system’s charging port via a cable.
If the auxiliary battery is connected, there is a particular feature to note during operation. This is because the small battery does not provide the full engine power. As soon as the drive operates in the lower-power ‘Range’ mode, the range extender is discharged. If you switch to Rally mode, the main battery is drawn upon. The logic behind this is that, with the range extender connected, only the auxiliary battery is used on the way to the trail spot or during transfer stages.
This means that full power and a fully charged main battery are available for the actual action. The remaining energy from the auxiliary battery then covers the journey home. This approach really brings out the sporty, race-inspired ethos that has shaped the system’s development. However, this approach also works well on longer rides, as you’re generally riding in ‘energy-saving mode’ for long enough to make the most of the extra 250 Wh.
How to use: The Pod Controllers
Wireless transmission is a major focus at SRAM. It goes without saying that the shifters used to control the Powertrain system also utilise AXS wireless technology. What’s more: rather than developing a new remote for motor control, SRAM is using the pods it introduced with the Eagle transmission. Two buttons on the left, two on the right: these allow the entire drivetrain – including the gears and motor – to be controlled. What’s more, they even an AXS telescopic seatpost from SRAM under control.
The functions of the buttons
As with other AXS components, the button assignments on the Eagle Powertrain can also be customised via the app. The following functions are provided as standard:
Right You change the cassette gears up and down as usual. Pressing and holding the top button activates or deactivates the automatic gear-changing function. At the bottom, you can press and hold the button to set the cadence that the automatic system uses as a reference.
The left-hand pod is intended for the telescopic seatpost at the bottom. Of course, this only works if an expensive Rockshox Reverb AXS is fitted. The upper button is used to switch between the two U-levels: Range and Rally. Holding it down activates the push assist. This is the only function that cannot be assigned to other buttons, as this is not permitted by law. Incidentally, the ‘Off’ mode – i.e. motor assistance switched off – cannot be selected via the pods. To do this, you must briefly press the top button on the display.
AXS Bridge Display
The approach to the display is similarly minimalist. In keeping with the modern style, the screen is recessed into the top tube, ensuring it is well protected and integrated in a sleek, unobtrusive manner. The AXS Bridge Display sits on top of the top tube, as the AXS antenna only receives signals ‘above ground’. Unlike the systems from Bosch (system controller) or Fazua (LED hub), SRAM features a stylish colour display. The look is reminiscent of to Specialized’s very successful TCU Mastermind.
The display is crystal clear and easy to read, even though it is rather small on the AXS Bridge. However, SRAM has opted not to include a wide range of display options, instead recommending ‘second-screen solutions’ such as GPS cycle computers, smartwatches or smartphones. All these devices can be paired via ANT+ and display data from the drivetrain system.
But back to the display itself. It shows the selected mode (Range: green; Rally: red), the Auto-Shift setting (ON: yellow; OFF: grey) and the battery level as a percentage. There are no other data fields, and the displayed data cannot be configured via the app. This means you have to do without standard data such as the time, speed, ride time or distance. SRAM has deliberately opted against multiple data pages, as this would have required an additional button to switch between them.
The display itself also has two buttons. A long (!) press of the main button switches the system on and off. If you press it briefly whilst the system is running, it switches to Off mode for riding without assistance or for servicing. The AXS button is located below the screen. A short press here allows you to switch back and forth between the U-levels. Holding it down activates pairing mode to connect the system to the AXS app.
The (automatic) gearbox: Eagle Transmission
The SRAM Eagle powertrain is only complete with the new SRAM Eagle drivetrain. After all, the real unique feature of the SRAM system is the communication and integration between the gear system and the motor. This enables two functions that are simply impossible with conventional gear systems and motors: Auto-Shift and Coast-Shift.
And this is precisely where the new Eagle Transmission is set to make all the difference. This is because the newly developed system focuses on shifting under load. Thanks to precisely defined gear changes, the transitions from one sprocket to the next are exceptionally smooth – even at maximum motor power. This allows the algorithm to select the right gear at all times, even during demanding e-MTB rides and on steep gradients.
Auto-Shift
Auto-Shift is a fully automatic gear-changing system. This means that the system handles gear changes entirely on its own. In theory, this means the bike can be ridden entirely without using the gear levers. To achieve this, a complex algorithm constantly monitors parameters such as riding speed, the current gear and motor power. The automatic gear-changing system attempts to keep the rider’s cadence within a specific range.
As preferences vary greatly in this regard, you can adjust the cadence. Top: It works very intuitively via the Pods. You don’t need an app and adjustments can be made quite easily whilst riding. By default, the cadence is set to ‘Mid’. From this mid-range setting, it can be slowed down by up to -3 or increased by up to +3. This gives you a choice of seven levels. SRAM does not specify exact values for the corresponding cadences. It is more of a range than an exact cadence.
Auto-Shift can be activated and deactivated by pressing and holding the top button on the right-hand pod. Even when the automatic mode is active, you can still change gears manually. In this case, the manual gear-change command temporarily overrides the automatic mode. This allows you, for example, to anticipate and respond to steep gradients ahead or to manually adjust your cadence.
Coast-Shift
The second feature enables gear changes whilst coasting. This is achieved by the motor driving the chainring without the cranks turning. This means you can shift into a heavier gear on a descent without having to frantically squeeze in extra crank revolutions on technical sections of the route. It can also offer real added value when braking before bends.
This function is particularly useful when Auto-Shift is activated. In that case, the system handles these processes entirely on its own. However, there are limits to this. On the one hand, the system takes a little time to respond. And secondly, gear changes are only possible whilst the rear wheel is turning. The slower it turns, the longer the gear changes take. That is, however, always the case with a derailleur system.
The sensor technology in the SRAM Eagle drivetrain
The bike’s speed is a crucial factor for the algorithm behind the automatic gear-changing system. To determine this as accurately and reliably as possible, SRAM uses not one, but six magnets on the brake disc. The plate into which the sensors are embedded is also particularly robust and fault-tolerant. However, it is not available for Centre Lock, but exclusively in the 6-hole design.
The AXS app
It’s hard to imagine a modern e-drive system without an app these days. This is all the more true of the SRAM Powertrain, as the AXS components can already be configured via the SRAM app. Fortunately, many settings on the new drivetrain can be adjusted without a smartphone, but not all of them. Adjusting the two assistance levels and customising the pod assignments require the AXS app.
Adjusting the power levels is even more important with this drive than with most other electric systems. This is because, with only two levels, there are only a few power settings to choose from. Even the weaker ‘Range’ mode already delivers very strong thrust in the factory setting and is therefore hardly suitable for energy-saving range-maximising rides. Two parameters can be adjusted via the app: maximum power and the percentage level of assistance – in other words, how hard the rider has to pedal to achieve full thrust. Of course, firmware updates can also be carried out via the app.
Bikes with the SRAM Eagle drivetrain
First things first: no bike featuring the new system has yet been unveiled to mark the launch of the SRAM Eagle Powertrain. Nevertheless, there are signs and details emerging about upcoming mountain bikes that go well beyond mere rumours.
To test the system, Sram provided us with Propain bearing the inscription “Ekano CF”, which looked quite well-developed. In the press pack for the launch, we also saw a bike with the bold lettering TRANSITION spotted. This vehicle, too, no longer looks like a prototype. From the world of motor racing, we know that apparently Gasgas and Nukeproof They’ve been tinkering intensively with bikes for the SRAM system for quite some time now. All these bikes give the impression of being entirely geared towards downhill riding.
First test: How the SRAM Eagle Powertrain’s automatic shifting system works
The ergonomics of the SRAM system are absolutely spot on; it’s simple and intuitive to use. The buttons fit comfortably in your hand and you quickly get the hang of how they work. The automatic gear-shifting function can also be switched on and off intuitively, and the desired cadence can be fine-tuned. Even whilst riding, without any fiddly app faff. This is what technological progress should look like, because not everyone wants to have to pull out their mobile before setting off.
Following that positive first impression, we turn our attention to the exciting Auto-Shift function. When riding at a leisurely pace, the automatic gear-changing system reacts more slowly than experienced cyclists would typically shift gears manually. As a result, the cadence doesn’t always hit the absolute sweet spot. On the plus side: with a single click, you can intervene and change gears yourself, and the automatic system will respect these rider preferences. However, once you get used to the new riding experience, you’ll find you can manage perfectly well without having to change gears yourself.
A longer test will show whether you get used to this new gear-changing logic – or whether you’re glad to be back in control. So far, we’ve only been able to put the system through a few test runs. The algorithm’s performance off-road is impressive. Here, the powertrain’s ‘brain’ sometimes reacts more quickly than when driving at a leisurely pace. Even really tough climbs are possible without ever touching the gear lever.
When the going gets steep and the engine is running at full throttle, that’s when the new Eagle Transmission comes into its own: the powertrain system shifts gears relentlessly, even when both the engine and the driver are at full throttle. And it does so extremely smoothly, sometimes almost imperceptibly. However, the gearbox must be optimally adjusted for this; otherwise, trouble is inevitable.
Automatic gear changes when going uphill
In automatic mode, you have to accept that the cadence won’t always be exactly what you’d select in manual mode. This can lead to awkward situations, particularly on gradated climbs: If you accelerate vigorously before a step, the automatic system detects a change in speed and sometimes shifts into a heavier gear. If things go wrong, the heavier gear is engaged just as the rear wheel catches on the step and your momentum is lost.
However, the high-torque motor comes in handy here, managing to haul the bike up the step even when in a gear that’s a bit too high. During our test rides, these situations did feel a bit awkward – but we never got stuck on an uphill climb because of them.
Furthermore, the system has logical limitations. Unlike the rider, it cannot anticipate what lies ahead. It only ever reacts to the immediate riding situation. If the road goes downhill briefly before climbing steeply again, Auto-Shift unnecessarily shifts up two gears, only to shift down four gears again on the climb – at a significantly lower cadence. These are gear changes you would never make in manual mode.
Coast Shift: Clear added value on the descent
The system offers significant added value on the descent. Thanks to the automatic Coast-Shift function, Powertrain always has the right gear ratio ready. When accelerating out of bends or building up speed before jumps, you don’t have to worry about the gear. It already works really well. A big plus.
Brose with SRAM software: Here’s what the motor feels like
Let’s take another look at conventional operation, without the automatic gear-shifting system. In terms of the SRAM motor’s performance characteristics, we could not detect any differences compared with other Brose motors, for example in the Specialized Turbo Levo, we found. Particularly at low motor output, the drive noise is quite quiet, significantly below Shimano and Bosch levels. However, at full power, even the belt-driven motor gets louder. A pleasant surprise: you can’t hear a thing going downhill! Our test bike from Propain glided silently over root-covered trails. This would be unthinkable with a current Bosch or Shimano drive system.
We have already praised the drive’s ease of use, but the Two levels of support seem to us to be too few. Even though we’re not fans of countless settings with fancy names, three modes at least make sense. A ‘Minimal’ mode that provides just a gentle nudge on the flat, making you forget the bike’s weight and its thick tyres. A ‘Medium’ mode for noticeable assistance with reasonable power consumption. And the full-throttle mode for extreme gradients, uphill challenges or a relaxed shuttle-like ride. In the factory setup, SRAM has omitted this lowest ‘Eco’ mode: ‘Range’ here is more akin to a medium trail mode.
Those who would rather not use the app for fine-tuning might even prefer modes that can be switched manually. Also missing we have the option of using the Pod to switch to ‘Off’ on the handlebars. Especially when there are only two gears, it can be useful on long rides to pedal through flat sections without motor assistance to save power. Admittedly, having to reach for the display in these situations is a minor inconvenience. Two wishes for the future: on technically challenging uphill sections, a (possibly app-activated) Trail help you manoeuvre the bike over steps more easily. We also felt that the push assist wasn’t quite up to scratch yet: holding down the top button on the left-hand pod requires quite a lot of force, and the push assist itself is a bit too tentative, especially on steep terrain.
Auto-Shift and Coast-Shift in the SRAM Eagle drivetrain: Who are they for?
Whether you like the Auto-Shift and Coast-Shift features of the new Eagle drivetrain is, not least, a question of riding experience, the type of terrain you ride on and getting used to them. Those who have had little experience with derailleurs so far will particularly appreciate the hassle-free shifting offered by the Auto-Shift function. Simply setting off on your e-MTB, venturing onto steeper terrain and not having to think about changing gears anymore – it works really well. Even on more relaxed transfer sections or uphill stretches, the system takes a lot of the work off your hands and enhances your comfort.
When it comes to genuine performance scenarios – racing, gruelling uphill challenges with stepped obstacles or sudden changes in gradient – the system is not really in its element. Experienced riders who enjoy tackling such terrain often make better decisions here, as they are able to anticipate what lies ahead. This ability – which is crucial in many riding situations – is completely lacking in the automatic gear-shift system. However, Coast-Shift can still offer real advantages even in this sportier context. Anyone wishing to change gears manually will need to get used to being able to shift whilst coasting. Selecting the right gear in this situation is harder than you might think. The automatic mode works really well here and almost always has a suitable gear ready.
CONCLUSION on the SRAM Eagle Powertrain
Motor, battery, display – the SRAM Eagle Powertrain doesn’t bring any innovation in these areas. But SRAM’s entry into the drivetrain market is a real game-changer. Its standout feature is the integration with the gear system. And the automatic gear changes really do work superbly. Anyone who finds shifting too much of a struggle in tricky situations, or who wants to focus more on other challenges, will love Auto-Shift. In particular, automatic shifting whilst coasting offers real added value on trails and descents. However, Auto-Shift has its logical limits and can therefore be a bit of a nuisance in some situations. It feels rather unfamiliar at first, particularly for experienced riders who are used to shifting gears frequently. The system only really comes into its own with the AXS dropper post and Eagle drivetrain – in other words, in the higher price bracket. Not everyone will be keen on the mere two gear ranges and the minimalist display. You don’t need to be a prophet to guess that the system won’t stop at its current stage of development. – Florentin Vesenbeckh, EMTB Test Manager
Pro
- Simple and intuitive operation
- The impressive Auto-Shift function
- (Automatic) gear changes whilst coasting offer real added value on trail descents (Coast-Shift)
- Smooth gear changes at all times
- Engine noise is subtle; no rattling when going downhill
Cons
- Just two levels of support
- Not much information on the display
- Automatic gear-changing has its logical limits, which can lead to incorrect gear changes in some situations (the system cannot predict what will happen!)
- It is only in the (expensive!) complete system, featuring Eagle Transmission and an AXS seatpost, that its full charm really comes into its own
We asked: Here’s what Sram says
EMTB: Who benefits from the Auto-Shift function?
Simon Kolmstetter: Auto Shift helps all e-mountain bikers to focus 100 per cent on the trail; this benefits beginners just as much as professional racers. What’s more, you can take control yourself at any time with just one click.
Two modes for motor assistance is very few compared with the competition. Why this minimalism?
We deliberately opted for a limited selection to make the controls intuitive. For sporty e-MTB riding, two modes are enough for us – ‘Range’ for relaxed cruising, and ‘Rally’ for maximum riding enjoyment off-road, whether on technical uphill sections or during sprints. The big advantage is that, without having to click my way through endless menus, I can switch to the right mode with just one click.
The display is also very minimalist; I can’t even get it to show my speed. What are the arguments against a more comprehensive display?
We firmly believe that, in this case, less is more, and have deliberately chosen this layout to prioritise ease of use. The display shows only the information relevant to sporty e-MTB riding, without causing any distraction. If you want more, you can pair Powertrain with your Hammerhead or other bike computers via ANT+ to view various parameters, such as speed, cadence or your power output in watts.
Brose’s Drive SMag has been on the market for five years now. Why was this supposedly outdated motor chosen?
The Powertrain project began with the development of one of the industry’s most advanced e-bike test benches. We scrutinised and put many systems through their paces. The Brose Drive SMag delivered the best combination of performance, noise levels and a natural riding experience. It is also very stable and can sustain its maximum power output for very long periods.
That’s true; the Brose is popular for its quiet and smooth operation. However, belt breaks and its mediocre reliability have also led to some negative press.
The faults mentioned occurred mainly in older versions of the motor and were also the result of specific software. We use the latest hardware with a redesigned belt and our own Sram software to prevent these faults. The system’s robustness is demonstrated not only by numerous practical and laboratory tests, but also by Yannick Pontal’s victory in last year’s EWS-E series.
Florentin Vesenbeckh
Editor CvD
