Gobs of power, stacks of range, wireless control, and integrated Auto Shift – there's a lot to like about SRAM's long-awaited entry into the motor market
SRAM’s entry into the e-bike arena marries motor and transmission for a match made in heaven. It’s no secret that SRAM has had an e-bike motor cooking for quite some time. Spotted racing with a prototype at the EWS-E last year was Nukeproof athlete Elliot Heap. Then SRAM acquired Amprio, a German motor brand. So while the product itself is no surprise the component giant is aiming to be among the best e-bike motors on the market, it’s what’s lurking beneath the covers that’s intriguing, and potentially divisive.
Need to know
- Integrates the e-bike motor with AXS wireless shifting system
- Wireless motor and transmission control with Auto Shift function
- Brose-built drive unit with 680W peak power and 90Nm of torque
- 630Wh and 720Wh battery options
- Only two power modes: Range and Rally
In recent years, SRAM has increasingly funnelled its components down the path of system-integration. By optimising individual parts to work together in a structured way, variables can be eliminated and performance can be enhanced. Except that mountain bikers notoriously hate being beholden to a specific brand, or system, when it comes time to replace worn or broken parts. But that’s a debate for a different day. The point is, Eagle Powertrain takes this strategy to new levels, which, depending on your viewpoint, is either extremely exciting or hugely frustrating.
SRAM’s new e-bike powertrain is designed to work exclusively with its new T-Type AXS transmission. To enjoy Eagle Powertain’s advantages, you have to go – if you’ll excuse the phrase – balls deep. Those advantages are two-fold: full wireless control of power modes, gear changes, and dropper post; and the potential to let the system shift for you, using Auto Shift and Coast Shift. Of course that’s not the full story, but these are the headlines that set SRAM’s offering apart from Shimano’s EP801, Bosch’s Performance CX, and Specialized’s similar Brose unit. With that in mind, let’s dive straight into the details.
Motor and battery
If you’ve owned or ridden a Specialized Turbo Levo (our current best E-Bike of the Year) then the SRAM motor will feel pretty familiar. It’s the same, physically chunky, 2.9kg, Brose motor used by Specialized, albeit running SRAM’s firmware. Four and six-bolt mounting options are available, and brands can make their own custom motor covers, but frame integration is a bit of a mixed bag depending on the bike brand. Of the models that will be available at launch, Nukeproof’s clocked design looks sleek, but Transition’s solution on the Repeater is definitely less elegant.
Top line stats on the motor are an impressive claimed peak power of 680w – far in excess of the 565w delivered in the Turbo Levo. And much higher than Shimano’s EP801 and Bosch’s Performance CX. At 90Nm, claimed torque also exceeds its two main rivals, even if it’s by just 5Nm.
To power the motor, brands can choose from two different capacity batteries. A smaller, lighter (3.1kg) 630Wh, or a larger 720Wh option (4.1kg). There’s also an optional 250Wh range extender with Fidlock mount.
SRAM steers clear of providing any estimates on range, but to give an idea, here’s what I achieved over two rides at Golfie in dry conditions on the Propain Ekano 2 29er shod with MaxxGrip Double Down tyres and fitted with the 630Wh battery. The first day was 1,451m of climbing and descending using both power modes. Day 2 was 1,567m in a mix of modes, completely emptying the tank in the process. On both days we rode some very steep climbs, which obviously puts more load on the motor and battery. In my experience, considering the gradients involved and the heavy-duty, slow-rolling, tyres fitted, that’s a very good result.
In another nod to the Turbo Levo, SRAM’s AXS Bridge display unit is integrated into the top tube and uses a small colour screen, protected by Gorilla Glass, to keep you informed of battery levels and current power mode. It has two buttons, one to turn the bike on, and the other to switch power modes. Compared to Specialized’s unit, the quantity of information it can display is more basic. At present you get to see the power mode, Auto Shift status, and battery percentage, both as an icon and a numerical figure. The font is quite small, so it’s not the easiest to read at a glance, and I’d prefer if the layout was customisable like the Turbo Levo display, maybe with the addition of a clock function just so you can see whether squeezing in one last lap is going to get you in trouble back home.
Utilising the current AXS pods, SRAM does away with the need for a custom motor controller. Being wireless, this keeps handlebars remarkably clutter-free, particularly in conjunction with SRAM’s Stealth brake levers. And the best thing is, such a clean cockpit can be achieved without brands having to resort to infuriating headset-routed internal cables.
If you’re familiar with AXS T-Type transmission and AXS Reverb droppers, then those basic functions are unchanged with Eagle Powertrain. Where the new system differs is control over power modes and the Auto Shift function. On the left side, the lower button controls your AXS dropper post. The top button toggles between Range and Rally modes, or hold it down to activate Push (walk) mode. Being the same size means it’s quite easy to hit the wrong button to activate the dropper post. I’d like to see SRAM offer a button with a larger surface area here, so you don’t kill the power when you want to drop your saddle.
On the right you can shift normally using the top and bottom buttons, or if you hold down the top button you can turn Auto Shift on and off. Holding down the lower button lets you change the calibration of Auto Shift.
Auto Shift and Coast Shift
While Shimano got there first with robotised shifting on its new EP801, SRAM goes one better by controlling it wirelessly. Well, I say wirelessly, but most e-bikes will come built with the rear mech tethered to, and powered by, the main battery via the Hot Shoe attachment.
Once operational, Auto Shift has seven different modes to choose from. From 0 you can go to +1, +2, or +3, for a bias towards higher cadences. In other words, it will let you spin the cranks at higher revs before deciding to shift to a harder gear. Go the other way, to -1, -2, or -3 and the system will shift into a harder gear earlier. The former is perhaps better for more technical terrain and more experienced riders, while the latter is aimed more at smoother, easier trails, and riders who prefer to let the motor do more of the work.
Complementary to Auto Shift is Coast Shift. In this instance the system can shift gears without you having to pedal, say, as you drop into a descent, or slow down into a corner. Theoretically, the system should ensure you’re in an optimal gear while simultaneously reducing the chance of pedal strikes.
App and Customisation
The final price of the puzzle is the AXS app. It’s here you can customise your settings and check battery status, among other things. It’s also the only thing we didn’t get to try during our time with Eagle Powertrain, since the app was still in Beta mode.
How it rides
Having spent a lot of time on Bosch motors recently, the most obvious aspect of Eagle Powertrain, from a motor perspective, was how smooth and quiet it is on rough descents. That muffled belt-drive and lack of clutch rattle is an absolute treat. And from a power perspective, the Brose/SRAM drive unit feels genuinely punchy. Before learning the claimed figures, I was seriously impressed by both the power and torque on tap. It’s a strong system, no doubt, and yet the range, even with the smaller battery and slow tyres, is impressive.
While the Bosch Performance CX can be tuned for a hair-trigger response, almost trembling in anticipation of a pedal input, the SRAM motor is calmer and less on-edge. It doesn’t fire out of the gates quite as quickly, but it picks up well enough at a wide range of cadences, and, once you’re moving, the power is very controllable on steep, technical climbs. Nor is there as much overrun as the Bosch, which may or may not be music to your ears. At Golfie I didn’t find it an issue, but on trails with less gradient and more obstacles it might be missed. Overall, I think SRAM has done a good job with its calibration, and my guess is that further opportunities for tuning will become possible in the future.
Now onto Auto Shift, and this is the controversial one. Plenty of people welcome the development of machine learning and the automation of previously manual tasks. Many others, quite rightly, dislike giving up control, or feeling like they’re being made redundant, or that big corporations are forcing them down a path they are not comfortable with. So let’s get one thing clear from the outset; Auto Shift is an option within the Powertrain system, not an obligation. You can use it or ignore it; it’s entirely up to you.
After two big rides on Auto Shift, I have a foot in both camps. And that may sound like a cop out, but I think it’s one of those systems that needs a little more time to evolve, and iron out the glitches. Let me give you a scenario. If you’re on a climb, and you’re approaching a kick in gradient, or a crux move over some rocks, chances are you’ll want to accelerate to generate more momentum to carry you up and over. So your cadence will increase, but you want to stay in a lower gear so you don’t get bogged down. Left to its own devices (dependent slightly on the setting) Auto Shift will detect the increased speed and higher cadence and shift up to a higher gear, and you’ll lose precious speed trying to turn that gear over before the system realises and shifts down again. By this stage you’ve had to put a foot down.
There are ways to override this happening, but the whole point of Auto Shift is to let you forget about shifting and focus all that extra mental and physical capacity at riding more smoothly. If you’ve got to change modes, manually change gears, or cancel shifts, that kind of defeats the purpose.
Of course the system can only respond to information it receives. It can’t look ahead down the trail. So this limits how it can react, and that’s where the hiccups occur. But, additional sensors within the motor (that are not used currently) may hold the key to unlocking a much more foolproof system.
Having said that, for the most part I was surprised by how effective Auto Shift was. Being able to forget about reaching for a shift button on a technical trail was truly liberating. And even when cruising up a fireroad climb or liaison trail, it was nice to completely relax. Coast Shift was equally welcome. Dropping into a tight trail, littered with stumps, and hearing the chain shuffle down the block was really cool. As was braking into a corner and not stalling on exit with the bike stuck in the 12t.
Finally, having spent a lot of time on AXS T-Type transmission, it was no surprise that shifting – whether automatically or manually – was smooth and precise whatever the load and gradient involved.
With a clatter-free motor, clutter-free cockpit, and clever functionality, SRAM’s Eagle Powertrain system is a welcome addition to the e-bike market. It offers some unique advantages, impressive performance, and will likely only get better as the firmware evolves.