Sram is entering the market of motor and e-drive manufacturers - this rumour has regularly surfaced in recent years. In the 2023 World Cup season was the Gasgas-Sram-Racing-Team around the German racer Johannes Fischbach already travelling with prototypes of the Sram system. But what exactly is behind it has remained a secret to the public until now. Now we can reveal all the details about the Sram Eagle Powertrain.
First of all: Sram has not developed a new motor of its own, but instead uses hardware from Brose. What is new about the Eagle Powertrain is the complete system and, above all, the networking and combination with the Eagle transmission gearstick. As with Shimano's EP801 and the new Shimano XT Di2 Sram is now also coupling the motor with the gears. The result and highlight of the Sram drivetrain: automatic shifting functions. Similar features are also available with the combined motor-gear unit MGU from Pinion 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 operation
- Eagle Transmission and the automatic gearstick
- The AXS app
- The bikes with Eagle Powertrain
- In the test: Eagle Powertrain and the automatic gearshift
- Conclusion, advantages and disadvantages
- Interview: What Sram says
The motor
For the motor, Sram uses tried-and-tested hardware from Berlin motor specialist Brose. The basis is the Drive SMagwhich Sram operates with its own software. Even though this motor is already a few years old, it is still one of the most powerful and, above all, quietest classic e-MTB motors on the market. It has a large fan base, not least in the very popular Specialized Turbo Levo.
At just over three kilos, it is not one of the lightest e-drives, but is only slightly above the level of Bosch's Performance CX. What's more, at 90 Newton metres, it has more torque than the competition from Bosch, Shimano and Yamaha (85 Nm each). Another advantage over the competition: the Brose is also quiet on the downhill, with no rattling disturbing the descent.
Special feature: The Sram motor only has two support levels, which have been named "Range" and "Rally". The idea behind this is to keep the operating logic as simple as possible. So that everyone can manage with just two levels, the modes can be fine-tuned in two parameters. This is done via the app, where the two parameters maximum power and support (how hard do I have to pedal to get full power) can be adjusted for each level using a slider.
This allows you to create a power-saving mode for flat stretches or ascents and descents to the trail. And a powerful mode for steep climbs and uphill challenges. Why this minimalism? One button is enough to switch back and forth between the two modes. And a simple operating logic with a clean cockpit was particularly important to the developers - but more on that later.
The facts about the Sram Eagle Powertrain
- Complete system comprising motor, battery, controls and Srams Eagle Transmission gears
- Automatic shifting functions possible (Auto-Shift and Coast-Shift)
- Two battery options with 630 or 720 watt hours
- Option of range extender on the down tube (250 Wh)
- Motor relies on Brose Drive SMag hardware (90 Nm max. torque)
- Two support levels "Range" and "Rallye" (both adjustable via app)
- Completely wireless operation via four buttons on the handlebars for all gearshift and motor functions
The batteries of the Sram Eagle Powertrain
The Sram drive works exclusively with the specially developed batteries. There are two variants to choose from: 630 watt hours for classic and convenient folding removal, or 720 watt hours for fixed integration or as a slide-in solution. At 3.1 kilos, the smaller version is very light in terms of capacity. The large 720 weighs 4.1 kilos. Both batteries rely on modern 21700 cells.
Sram has also developed a range extender. This means that 250 watt hours can be accommodated on top in the frame triangle. However, the compact battery does not fit into a normal bottle cage, as is usual with some competitor products. A separate, robust and, according to Sram, completely rattle-free bracket is attached to the bottle cage screws. An adapter plate for a bottle cage can also be clicked in here to easily switch between water bottle and range extender operation. The additional battery is connected to the charging port of the Powertrain system via a cable.
If the additional battery is connected, there is a special feature during operation. This is because the small battery does not provide the full engine power. As soon as the drive is running in the weaker range mode, the range extender is discharged. If you switch to Rally mode, the main battery is tapped. The logic behind this: With the range extender plugged in, only the additional battery is used on the way to the trail spot or on transfer stages.
The full power and the full main battery are then available for the actual action. The remaining energy from the additional battery then bridges the way home. With this logic, you can feel the sporty racing mindset that has determined the development of the system. However, you won't have any problems with this logic on longer tours, as you are usually travelling in "energy-saving mode" enough to make use of the additional 250 Wh.
Operation: The Pod Controller
Wireless radio transmission is the big topic at Sram. It goes without saying that the shifters used to control the powertrain system also rely on AXS wireless technology. What's more, instead of developing a new remote for the motor control, the pods that Sram introduced with the launch of the Eagle Transmission are used. Two buttons on the left, two buttons on the right: this allows the entire drivetrain with shifting and motor to be controlled. In addition, it is even possible to an AXS dropper post 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 shift the gears of the cassette up and down as usual. A long press on the upper button activates or deactivates the automatic shifting. At the bottom, a longer press allows you to set the cadence to which the automatic system is orientated.
The left pod is provided at the bottom for the dropper post. Of course, this only works if an expensive Reverb AXS from Rockshox is fitted. The upper button is used to switch between the two U-stages Range and Rally. Pressing and holding it activates the walk 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 have to briefly press the top button on the display.
AXS Bridge Display
The approach to the display is similarly minimalist. In modern style, the screen is embedded in the top tube and is therefore well protected and visually slim. The AXS Bridge Display sits on the top tube, as the AXS antenna only receives signals "above ground". In contrast to the systems from Bosch (system controller) or Fazua (LED hub), Sram has implemented a stylish colour display. The look is reminiscent of to the very successful TCU Mastermind from Specialized.
The display is razor-sharp and easy to read, even if it is rather small on the AXS Bridge display. However, Sram does not offer a wide range of display options and instead refers to "second screen solutions" with GPS computers, smartwatches or smartphones. All of these devices can be connected via ANT+ and display the data from the drive system.
But back to the actual display. The display 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. You therefore have to do without classic data such as time, speed, journey time or distance. Sram deliberately decided 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 on the main button switches the system on and off. A short press during operation switches the system to off mode for riding without assistance or for service work. The AXS button is located below the screen. With a short press, you can switch back and forth between the U levels. Pressing and holding activates pairing mode to connect the system to the AXS app.
The (automatic) gearstick: Eagle Transmission
The Sram Eagle Powertrain is only complete with the new Sram Eagle Transmission gear system. The real speciality of the Sram system is the communication and networking of the gears and motor. This enables two functions that are simply impossible with conventional gears and motors: Auto-Shift and Coast-Shift.
And this is precisely where the new Eagle Transmission should make the decisive difference. This is because the newly developed system focuses on shifting under load. Thanks to defined gear changes, the shifts from one sprocket to the next are actually particularly smooth - even at maximum engine thrust. This allows the algorithm to engage the right gear at all times. Even in tough E-MTB use and in the middle of steep gradients.
Auto-Shift
Auto-Shift is a fully automatic gearstick. This means that the system changes gears completely independently. This means that the bike can theoretically be ridden completely without a gear lever. A complex algorithm constantly monitors parameters such as the speed being ridden, the gear engaged and the motor power. The automatic shifting system attempts to keep the rider's cadence within a certain range.
As preferences vary greatly here, you can adjust the cadence. Top: It works very intuitively via the pods. No app is needed and adjustment can be carried out in a relaxed manner while driving. The cadence is set to "Mid" as standard. From this average value, it can be slowed down to -3 or accelerated up to +3. There are seven levels to choose from. Sram does not specify concrete values for the corresponding cadences. This is more of a bandwidth than an exact cadence.
Auto-Shift can be activated and deactivated with a long press on the top button on the right-hand pod. Manual shifting is also possible when the automatic mode is active. The manual shift command then overrides the automatic system for a short time. This allows you to react proactively to steep gradients ahead, for example, or to manually readjust the cadence.
Coast-Shift
The second feature makes it possible to shift gears while rolling. The chainring can be driven by the motor without the cranks turning. This allows you to engage a heavier gear on the descent without having to frantically squeeze in crank revolutions on technical sections. This can also offer real added value when braking before bends.
This function is particularly helpful when Auto-Shift is activated. This is because the system then takes care of these processes all by itself. However, this has its limits. On the one hand, the system needs some time to react. And on the other hand, gear changes are only possible as long as the rear wheel is turning. The slower it turns, the longer the gear changes take. However, this is always the case with derailleur gears.
The sensors in the Sram Eagle Powertrain
The speed of the bike is a decisive factor for the algorithm behind the automatic shifting system. In order to determine this as precisely and accurately as possible, Sram uses six magnets on the brake disc instead of just one. The plate in which the signal transmitters are embedded is also particularly robust and error-resistant. However, it is not available for centre lock, but only in a 6-hole design.
The AXS app
A modern e-drive without an app is almost unthinkable. This is all the more true with the Sram Powertrain, as the AXS components can already be adjusted via the Sram app. Fortunately, many settings on the new drive system can also be made without a smartphone, but not all of them. The AXS app is required to adjust the two support levels and also the individual assignment of the pods.
Setting the speed levels is even more important with this drive than with most other e-systems. Because with only two levels, there are only a few motor strengths to choose from. Even the weaker range mode is already very powerful in the factory setting and is therefore hardly suitable for energy-saving range hunting. Two parameters can be set via the app: Maximum power and percentage of assistance, i.e. how hard the rider has to pedal for full thrust. Firmware updates are of course also possible via the app.
The bikes with Sram Eagle Powertrain
First things first: At the launch of the Sram Eagle Powertrain, no bike with the new system has yet been unveiled. Nevertheless, there are signs and information about upcoming mountain bikes that go well beyond the rumour status.
To test the system, Sram provided us with a Propain labelled "Ekano CF", which made a fairly sophisticated impression. In the press documents for the launch, we also found a bike with the bold letters TRANSITION spotted. This vehicle no longer looks like a prototype either. We know from racing that apparently Gas gas and Nukeproof have been working intensively on bikes for the Sram system for some time. All of these bikes make an absolutely downhill-orientated impression.
First test: How the automatic shifting of the Sram Eagle Powertrain works
The ergonomics of the Sram system are absolutely perfect, the operation is simple and intuitive. The buttons sit comfortably in the hand and the operating logic is quickly understood. The automatic shifting can also be intuitively switched on and off and the desired cadence fine-tuned. Even while driving, without any annoying app fiddling. This is what technical progress should look like, because not everyone wants to have to pull out their mobile phone before setting off.
After the positive first impression, we will concentrate on the exciting auto-shift function. The automatic shifting reacts more slowly in leisurely riding mode than experienced bikers would usually shift manually. This means that the cadence doesn't always hit the absolute sweet spot. Good: You can help out with a click and shift gears yourself; the automatic system also fulfils these rider wishes. However, if you get used to the new riding experience, you can manage wonderfully without your own shifting commands.
A longer test will show whether you get used to this new switching logic - or whether you are happy to be in control again. So far, we have only been able to take the system on individual test runs. The function of the algorithm off-road is impressive. Here, the Powertrain brain sometimes reacts faster than when pedalling at a leisurely pace. Even really nasty climbs are possible without even touching the gear lever.
When the going gets tough and the engine is running at full throttle, the new Eagle Transmission comes into its own: the Powertrain system shifts gears mercilessly, even when the engine and driver are at full throttle. And this happens extremely smoothly, sometimes almost unnoticed. However, the gearstick should be optimised for this, otherwise trouble is inevitable.
The automatic gearstick on the uphill
In automatic mode, you have to accept that the cadence is not always exactly the same as you would select in manual mode. This can lead to unfavourable situations, especially on steeper climbs: If you accelerate vigorously before a step, the automatic system recognises a change in speed and sometimes shifts to a harder gear. If things go badly, the heavier gear is engaged exactly when the rear wheel is hanging on the step and the momentum has fizzled out.
However, the particularly high-torque motor helps here, lifting the bike over the step even with a gear that is a little too high. During our test rides, these situations did not feel harmonious - but we never got stuck on the climbs because of this.
The system also has logical limits. Unlike the driver, it cannot look ahead. It only ever reacts to the current driving situation. If you only go downhill for a short time and then start climbing steeply again, Auto-Shift unnecessarily shifts two gears harder, only to shift four gears easier again on the climb - at a cadence that is clearly too low. Gear changes that you would never make in manual mode.
Coast Shift: Clear added value in the downhill run
The system offers significant added value when travelling downhill. Powertrain always has the right gear ratio ready via the automatic Coast-Shift. When accelerating out of bends or accelerating before jumps, you don't have to worry about the gear. This already works really well. A big plus.
Brose with Sram software: How the motor rides
Let's take another look at classic operation away from the automatic gearshift. We could not find any differences in the characteristics of the Sram motor compared to other Brose motors, for example in the Specialised Turbo Levo. Especially at low motor thrust, the drive noise is quite quiet, well below Shimano and Bosch levels. However, at full power, even the belt-driven motor becomes louder. Pleasant: Absolutely nothing can be heard downhill! Our test bike from Propain glided over root carpets as quiet as a whisper. Unthinkable with a current Bosch and Shimano drive.
We have already praised the simple operation of the drive, but the Two support levels seem too little to us. Even if we are not fans of countless levels with fancy names: Three modes at least make sense. A minimum mode that only provides a slight push on flat terrain and makes you forget about the bike's weight and fat tyres. A medium mode for noticeable thrust with tolerable power consumption. And the full throttle level for extreme climbs, uphill challenges or a relaxed shuttle feeling. In the factory setup, Sram dispenses with this lowest Eco level: Range is more like a medium trail mode here.
Those who prefer not to fine-tune via the app might prefer even more manually switchable modes. Also missing we have the option of using the pod switch to Off on the handlebars. Especially with only two gears, it can be useful on long rides to crank down flat sections without motor thrust to save power. Admittedly: In these cases, reaching for the display is not a problem. Two wishes for the future: On technical uphills, a (possibly switchable via app) Overrun help to balance the bike better over steps. We didn't find the push assist to be ideal either: holding down the upper button on the left pod requires a lot of force and the push assist itself is too hesitant, especially on steep terrain.
Auto- and Coast-Shift in the Sram Eagle Powertrain: Who is it for?
Whether you like the Auto and Coast Shift features of the new Eagle Powertrain is not least a question of riding experience, area of use and familiarisation. Anyone who has hardly any experience with derailleur gears will enjoy the carefree shifting behaviour of the Auto-Shift function. Just go for a ride on the E-MTB, dare to tackle steeper terrain and no longer have to think about shifting gears - it works really well. Even on more relaxed transfer or uphill sections, the system does a lot of the work for you and increases comfort.
In the real performance area - racing, nasty uphill challenges with stepped obstacles or sudden changes in gradient - the system is not really at home. Experienced riders who enjoy travelling on such terrain often make the better decisions here. This is because they can act with foresight. This ability, which is crucial in many driving situations, is completely lacking in the automatic gearshift. However, Coast-Shift can also bring real advantages in this sporty area of application. If you want to engage the gears manually, you have to get used to being able to change gear while rolling. Hitting the right gear here 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 here. But Sram's entry into the drivetrain market is a cracker. A special feature is the networking with the gears. And the automatic gear changes really do work brilliantly. Anyone who is overwhelmed by shifting gears in difficult situations or wants to focus more on other challenges will love Auto-Shift. In particular, the automatic shifting while rolling brings real added value on trails and descents. However, Auto-Shift has logical limits and can be annoying in some situations. Especially for experienced bikers who have learnt to shift gears a lot, this can be unfamiliar at first. The system only really comes into its own with an AXS dropper post and Eagle Transmission drivetrain - i.e. in the expensive price segment. Not everyone will like the minimalist display and only two gear steps. You don't have to be a prophet to guess that the current expansion stage of the system will not be the end of the story. - Florentin Vesenbeckh, EMTB test manager
Pro
- Simple and intuitive operation
- Impressive function of the automatic gearshift (Auto-Shift)
- (Automatic) coasting shifting brings real added value on trail descents (Coast-Shift)
- Smooth gear changes at all times
- Discreet engine sound, rattle-free downhill
Contra
- Only two support levels
- Little information on the display
- Automatic gearshift has logical limits, which provokes incorrect gearshifts in some situations (system cannot look ahead!)
- Only in the (expensive!) complete system with Eagle Transmission drivetrain and AXS post does the full charm unfold
Inquiry: What Sram says
EMTB: Who benefits from the auto-shift function?
Simon Kolmstetter: Auto Shift helps all e-mountain bikers to focus 100% on the trail, which benefits beginners and professional racers alike. You can also take command yourself at any time with just one click.
Two modes for motor support are very few compared to the competition. Why this minimalism?
We have deliberately opted for a reduced selection in order to make operation intuitive. For sporty E-MTB use, two modes are enough for us - Range for relaxed cruising, Rally for maximum riding fun off-road, whether technical uphill or intermediate sprints. The big advantage is that I can switch to the right mode with a single click without having to click through endless menus.
The display is also very minimalistic, I can't even see the speed. What's wrong with a more comprehensive display?
We are convinced that less is more and have deliberately opted for this layout in favour of ease of use. The display only shows the information that is relevant for sporty E-MTB use without being distracting. If you want more, you can connect Powertrain to your Hammerhead or other bike computer via ANT+ to display various parameters such as speed, cadence or your own power in watts.
The Drive SMag from Brose has been on the market for five years. Why was this supposedly old motor chosen?
The Powertrain project began with the development of one of the most modern e-bike test benches in the industry. We scrutinised many systems and put them through their paces. The Brose Drive SMag delivered the best package of performance, background noise and natural riding feel. It is also very stable and delivers its maximum power for a very long time.
That's right, the Brose is popular for its quiet and smooth operation. However, belt tears and poor reliability have also made negative headlines.
The defects mentioned occurred mainly with older versions of the motor and were also the result of specific software. We use the latest hardware with a revised belt and our own Sram software to avoid these errors. The robustness of the system is proven 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
