Test / E-MTB drive: With the Sram Eagle Powertrain, the US component giant is now entering the area of E-MTB drives. The system relies on the well-known Drive S Mag motor from Brose, but embeds it in its own ecosystem that has numerous features. We were able to try out the drive before it was launched on the market.
It has been rumored for years as to when Sram would introduce its first drive for e-bikes - today is the day. The Sram Eagle Powertrain brings with it many things that industry experts would expect, but it also has some features that only very few people would have considered. As the name of the system suggests, Sram attaches great importance to integration into the Eagle cosmos, including switching and operation.
Old friend at the engine
What is quite surprising at first is that Sram relies on a well-known solution for the motor - after all, the heart of the drive: the Brose Drive S Mag provides propulsion within the system. Although the automotive giant's mid-engine has been on the market for several years now, it can still keep up with some of its much younger competitors and still occupies a unique position in some respects. In terms of power, on paper it is even slightly better than its competitors from Bosch, Shimano and Co, with up to 90 Nm; The maximum power we measured shows that it sits pretty much between the Bosch CX and Shimano EP8.
However, raw performance was never what allowed the Brose Drive S Mag to earn its special position on the market. Above all, it is its natural driving behavior and its unrivaled low operating noise that has earned the engine a large fan base to this day, despite its initial susceptibility to defects. These problems from the early years have now been addressed in both hardware and software. The drive belt installed inside has been reinforced, and software adjustments eliminate load peaks. SRAM also placed a lot of emphasis on the latter when developing the software in order to ensure maximum reliability. In addition, the drive has of course been given its own unique software stamp, even though no fundamental changes have been made to either the maximum performance or the basic characteristics of the engine.
Only two levels of support
Perhaps the biggest change to known drives with the Brose Drive S Mag are the support levels of the Sram Eagle Powertrain: The Americans reduce these to an absolute minimum and only offer two of them: 'Range' and 'Rally'. There are probably two main reasons for this decision. On the one hand, the aim is to make the operation of the drive as intuitive as possible, and on the other hand, the controls can be designed to be even more reduced - one button is enough to switch between the two support levels.
For operation, Sram uses its own portfolio: The AXS Pod presented with the Eagle Transmission circuits acts as a control center for the electric drive, of course also wirelessly. One of the two buttons is sufficient to change the support level, the other can be used, for example, to operate an AXS Reverb seat post.
AXS Bridge Display as a control center
Both the AXS Pod and the drive itself communicate with the system's control center in the top tube, the new AXS Bridge Display. Integrated into it is an unfortunately quite small color screen that provides information about the battery charge level, the selected support level and also the selected automatic mode. Unfortunately, the content of the display cannot be customized using the AXS app. However, the system does offer an ANT+ interface that transmits further information such as cadence or speed to compatible devices from Hammerhead, Garmin, Wahoo and Co.
Two battery sizes and range extender
When it comes to energy supply, bicycle manufacturers have the choice between two integrated batteries with 630 Wh or 720 Wh. Their integration into the frame is up to the respective manufacturer. They can be permanently installed or removed via a classic flap or as a slide-out solution in the bottom bracket area. At around 3 kg for the 630 Wh version and around 4 kg for the larger battery, the weights are in the range of what is known from the competitors - only the Bosch batteries are a few grams heavier.
In addition, the Sram Eagle Powertrain also offers the option of a range extender with an additional 250 Wh capacity. This is attached to the bottle holder via its own mounting plate - rattle-free, that's what Sram promises. The additional battery is then connected to the charging port of the bike using a cable. However, it should be noted that the range extender is only used in range mode. Specifically, this means: If you drive in the low support level, the system first only empties the range extender, then the main battery. In rally mode, only the main battery is tapped - if it is empty, the system automatically switches to range mode and switches to the range extender.
Automatic and Coast-Shift in conjunction with Eagle Transmission
However, part of the drive system in the Eagle Power Train is not just the components surrounding the engine, but also the circuitry. As the name suggests, the electric drive is part of the Eagle ecosystem and communication between all components also takes place via the AXS Bridge Display. Provided you are using one of the new Eagle Transmission gears, because mechanical gears can be combined with the Eagle Powertrain just like the “old” AXS gears, but you have to do without the automatic features.
Two functions in particular are in the spotlight here: Auto-Shift and Coast-Shift. When Auto-Shift is activated, gears are changed fully automatically depending on speed and cadence. Manual intervention is of course just as possible as completely deactivating it. In order to provide an automatic system that is also suitable for sporting use, SRAM has spent a long time fine-tuning the corresponding algorithms. As a driver you also have the option of setting the target cadence in a total of seven levels. Starting from the standard setting, this can be easily adjusted directly on the bike up to +3 or -3, depending on your preferences and terrain.
No less exciting is the Coast-Shift function, which is already known under the name Free-Shift from Shimano and the new XT Di2: This allows you to change gears even when you are not pedaling. To do this, the motor drives the chainring briefly so that the chain can move onto the corresponding sprocket on the rear wheel. As a driver, you don't notice any of this - a really cool feature, for example to select the right gear for the uphill climb during the descent. The Sram Coast-Shift function is always activated in connection with transmission shifts, even if you are not using the automatic system.
Updates and customization via AXS app
If you connect the Sram Eagle Power Train to the well-known AXS app on your smartphone, you can, among other things, individualize the support levels. Here you can set both the support factor and the maximum power for both support levels. In range mode, the power is capped at a maximum of 540 W. The buttons on the AXS Pod can also be assigned here, as can software updates for the drive.
Four models to start with Sram Eagle Powertrain
When the new drive system launches, four e-MTBs with the Sram Eagle Powertrain will be available. In addition to the Propain Ekano CF that we rode, there will be a new Transition Repeater and also E-MTBs from Gasgas and Nukeproof. Details about the individual models will only be available in the coming weeks - but what they all have in common is their basic sporty orientation and large spring travel reserves.
The Sram Eagle Powertrain in the first test
We were able to test the new Sram Eagle Powertrain on a detailed trail lap at Sram's front door in Schweinfurt. The first thing you notice is that the Brose Drive S Mag is still a really convincing engine. Above all, the pleasant background noise is a blessing: our test bike, the Propain Ekano CF, was probably one of the quietest E-MTBs that we have ever ridden in the past few months. Uphill, even high performance and high cadence elicit no more than a quiet hum from the 2,9 kg engine, while downhill the noise is limited to the full rolling of the tires - that's how it has to be!
In terms of performance, the Drive S Mag can also keep up with the competition in 2023, even if it works more gently and naturally than brutally. So if you expect enormous acceleration right from the start, you might be a little disappointed. However, the performance is there, even at low cadence. The fact that the system only offers two levels of support leaves us conflicted. On the one hand, the operation is really wonderfully intuitive and in most cases there are enough two levels - especially since you can also configure these using the AXS app. However, every now and then you get into a situation where you are slightly below the “well-being support” in one level and slightly above the “well-being support” in the other.
For most of the test lap, which lasted approximately two hours, we had Auto-Shift activated. What is immediately noticeable here is that the automatic system generally reacts rather slowly to changing requirements. However, this is by no means meant in a negative way: If the gears were to acknowledge every slight fluctuation in cadence, for example in a small dip, with gear changes - the result would be hectic and less than natural driving behavior. Instead, the system waits a long time until it moves the chain onto a suitable sprocket. This can also lead to you initially traveling for a few meters in a gear that is too difficult on a counter climb. Here you can either intervene manually or rely on the motor support for a short time.
Alternatively, the target cadence can be quickly adjusted while riding or even on the trail thanks to the individual controls. We made use of this once when the automatic transmission kept changing into a gear that was too difficult on a steep section after our manual gear changes. Overall, the automatic performance is surprisingly good, even off-road: but do sporty e-mountain bikers really use it off-road? This will be very individual. A feature that is always practical and never annoying is the excellently functioning coast shift. You get used to changing gears while descending almost shockingly quickly.