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SRAM Eagle Powertrain Flies Auto-Shift & Coast-Shift | First Ride

sram eagle powertrain ebike motor srive unit complete system inside nukeproof
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After much speculation and many a spy shot, SRAM has unveiled the Powertrain, powered by Brose. To be clear, this is not just another eBike Motor. Designed to work optimally with the electronic Transmission groups as a complete system, the Powertrain is able to offer heaps more than pedal-assistance. Written into its firmware are some seriously high-tech features; the auto-shift and coast-shift functions are engineered to enrich the ride experience by handling gear changes for you.

Indeed, the Powertrain not only automatically shifts for you while you’re pedalling, it also shifts for you while you’re coasting. And you, the rider, can tailor how it does that.

nukeproof megawatt sram powertrain emtb 720wh battery 90nm torque
SRAM Powertrain has arrived. Credit: Rupert Fowler – Mountain Bike Connection Summer

The SRAM Powertrain will launch on four new e-mountain bikes over the coming months, the first of which is the Nukeproof MegaWatt seen throughout.

Happily, we had the good fortune to test ride this latest eBike tech just last week, at a Bike Connection Agency event in Andalo, Italy. Details on the MegaWatt will remain sparse, for now. Here, we turn our attention to the tech and specs of its engine room, along with our first ride review of its performance up and down the mountain.

sram eagle powertrain ebike motor system inframe

SRAM Eagle Powertrain | An Overview

From a hardware point of view, the SRAM Eagle Powertrain is a Brose motor. But, critically, from a software and firmware point of view, it is very much a SRAM creation.

With a maximum torque of 90 Nm, the Eagle Powertrain is one of the more powerful mid-drive motors on the market; that’s 5 Nm more torque than the Shimano EP801, or the Bosch Performance Line CX Systems. Its peak power output is high, too. It comes in at 680 Watts versus the 600 Watts boasted by either of the aforementioned. SRAM refrain from quoting a specific percentage for assistance.

sram eagle powertrain ebike motor
Powertrain will assist riders up to a maximum speed of 25 Km/h in Europe and 20 mph (32 Km/h) North America. Credit: SRAM.

Key Stats

  • eBike System: SRAM Eagle Powertrain
  • Ride Modes: Range, Rally, and Push
  • Extra Features: Auto-Shift and Coast-Shift, for Transmission only
  • Maximum Torque: 90 Nm
  • Peak Power Output: 680 Watts
  • Batteries: 630 Wh, 720 Wh (+ 250 Wh Range Extender)
  • Drive Unit Weight: 2.9 kg
  • Warranty Period: Two Years

Though the system is at its best when paired with Transmission, the motor is still very much compatible with mechanical groupsets, as well as the other AXS groups. Only with Transmission do you get the benefits of Auto-Shift and Coast-Shift.

Broadly speaking there are three main batteries; a 4.1 kg 720 Wh battery (175.6 Wh/kg), a 3 kg 630 Wh battery (210 Wh/kg), and a 250 Wh Range Extender. The 630 Wh is likely to find its way onto lighter eBikes, offering the more favorable capacity to weight ratio. And, smaller frame sizes of the “full fat” eBikes, of course, where there’s insufficient room for the 720 Wh battery.

sram 720 wh battery slides out from downtube
SRAM’s 720 Wh and 630 Wh batteries both have 21,700 cells. The former takes around 5 hours to charge, while the latter takes around 4.5 hours. Credit: Rupert Fowler – Mountain Bike Connection Summer

Frame manufacturers will have the option to have a main battery that slides in from underneath, pops out via a door on the downtube, or one that is not removable.

On the topic of batteries, the Powertrain system does mean the T-Type derailleur no longer needs one of its own.

sram xo transmission t-type derailluer no battery
On Powertrain x Transmission-equipped eMTBs, the T-Type derailleur loses its battery, as it is wired directly from the Powertrain system. The AXS Reverb Dropper post still requires its own separate battery. Credit: Rupert Fowler – Mountain Bike Connection, Summer.

The Central Processing Unit

At the heart of the SRAM Eagle Powertrain is the AXS Bridge Display, integrated into the bike’s top tube. It is ever so slightly raised relative to the top tube to ensure the best possible connection between the various components. This is where you turn the system on or off, and where you can see whether you’re in Range or Rally mode, as well as the charge status of the battery (or batteries).

sram eagle powertrain axs bridge display
The AXS ecosystem means Flight Attendant is compatible with Powertrain, too. On a Flight Attendant-equipped bike, the drive unit itself will function as the pedal sensor. Credit: Rupert Fowler – Mountain Bike Connection Summer

There is no additional display unit on the bar, or wires running into headtube. SRAM packs all the controls into the AXS Bridge Display and two wireless Pod Controllers on the bar, giving an impressively clutter-free cockpit. In my opinion, the SRAM Eagle Powertrain wins hands-down on aesthetics.

Data enthusiasts need not be dismayed; the option remains to pair the system with a Hammerhead, Garmin or other third party device. That way, you’ll still be able to see other stats like speed, cadence, remaining range, rider power and current gear selection.

Being the brain of the system, the AXS Bridge Display collates data from torque and cadence sensors in the motor, and a high-resolution speed-sensor on the rear wheel. As per, that data is used to make decisions on how much torque should be delivered to the rear wheel. And, when paired with Transmission, it is also used to make Auto-Shift and Coast-Shift decisions.

Powertrain Brings SRAM Bang Up To Date

Indeed, Auto-Shift and Coast-Shift aren’t particularly novel. Shimano has implemented similar features on their latest eBike system. I am yet to ride that system myself, so I will refrain from making any ill-informed comparisons between the two – however, should you want more information on how Shimano’s offering performs on the trail, you can read Cory’s in-depth review here.

These are some of the more interesting features of the Eagle Powertrain. SRAM could very well have just launched a Drive Unit alone, implementing high-end features at a later date. But, given the capability of Transmission, and the inter-connectivity of the AXS ecosystem, they’ve gone right ahead with a product set to compete with Shimano’s EP801 XT Di2 combination.

Thirteen years after Shimano first announced the E6000 STePS Unit, SRAM has finally launched its very first eBike motor. Our take? It’s very good, but I’m relieved that some of the bonus features are optional, not obligatory…

riding sram powertrain nukeproof megawatt dolomites 2023
Credit: Rupert Fowler – Mountain Bike Connection, Summer.

First Ride | SRAM Powertrain

Unlike many eBike systems, the SRAM Eagle Powertrain has just two main riding modes, aptly named Range and Rally. As you might expect, Range delivers relatively less assistance in response to the rider’s input, while Rally delivers relatively more. Both modes are tuneable via the AXS App, and there’s rather a large range of adjustment on offer.

sram powertrain range rally mode adjustment axs app interface

Rather than having a number of discrete settings for assistance, SRAM use a continuous slider so the rider can dial in exactly how much assistance they want in Rally and Range. Out of the box, Rally mode is set to 80% assistance, giving 600 Watts at maximum power, but that can be moved right up to 100% for the full unbridled 680 Watts of assist.

sram eagle powertrain first ride review technical climbing out of saddle
The longest cranks for Powertrain are 160mm; shorter options may follow in future, but nothing longer. Credit: Rupert Fowler – Mountain Bike Connection Summer

Technical Climbing

I did all of my technical climbing in Rally mode, set to 80% assist. The power was certainly not wildly unmanageable at any point. It seemed nicely measured most of the time and I was able to ride steep, bumpy sections with ease. The exception to that would be the odd occasion where the rear wheel spun out while trying to find grip on wet limestone. That stuff is the epitome of anti-grip, by the way.

For me, an eBike is never going to deliver a “natural” pedaling experience, despite what you may read in marketing material everywhere. That said, the power delivery of the SRAM system never did anything weird or unexpected. It never really felt as though it was running away from me.

There’s a gentle ramp of torque delivered between pedal strokes, so it doesn’t feel like a violent, wild horse. It’s a little smoother than the Shimano EP801 in that regard. Oh, and it’s a fair bit quieter, too. That’s true for going up and down the hill. The motor’s whir is less pronounced, and there’s no rattle while descending. Very pleasing.

When you stop pedaling, the drive unit reacts reasonably quickly to stop delivering torque to the rear wheel. There is a small amount of intentional lag, but very little compared to what you get from the “Extended Boost” feature on the Bosch Performance Line CX Race.

I’ll not pretend i’m any kind of eBike specialist, preferring to do almost 100% of my riding unassisted. But, in the context of what it is? Yeah, OK, I really liked it.

sram axs bridge disaplay rally mode cadence setting +3 battery status 43%
Credit: Rupert Fowler – Mountain Bike Connection Summer

Auto-Shift is a “Nice to Have”

On a first ride of the system, the Auto-Shift function is not quite as automatic as the name might lead you to believe. That’s because there are no fewer than seven cadence modes to choose from.

To name them: -3, -2. -1, MID, +1, +2, and +3. In the -3 mode, the system prioritizes a slow pedalling cadence, and will auto-shift to ensure cadence remains low. At the other end of the spectrum, the +3 mode will prioritize the highest cadence, and will auto-shift accordingly.

You may well wonder what the exact cadence ranges are for each setting. SRAM says there is no strictly-defined range for each mode.

Pedaling out of the yard in the -3 setting, I quickly realized the system was forcing a cadence that was significantly below what I like. The setting is easy to change on-the-fly; you simply press and hold the lower button on the right Pod Controller, after which you can use the buttons on that same controller to toggle through the auto-shift settings. Pedaling on a flat road, I toggled to the +2 setting where the system is biased toward a much higher cadence.

Actually, I found the +2 setting to be best for almost all of the afternoon’s test ride. The highest +3 setting was arguably better suited to the steepest climbs, but it would force too high a cadence on flatter sections, or more gentle fire road climbs. I found that if I just wanted to ease along without speeding up, +1 or +2 were best.

I can’t fathom who might settle for one of the slower cadence modes, but SRAM say the modes were decided based upon rider feedback.

Auto-Shift Can’t Predict the Future, But You Can

The auto-shift seemed to perform very well in most scenarios. There is a short lag experienced when the system is required to shift to an easier gear when the gradient tips up. It needs to see that your pedalling cadence has slowed in response to the gradient before it can react. At the risk of stating the obvious, the Eagle Powertrain doesn’t have eyes. It can’t predict what’s coming up, but you can.

Indeed, you can take matters into your own hands at any point in time, over-riding the system by manually initiating a shift in the usual way. Or, you can just wait (no more than) a second, and the system will auto-shift. Shifting is ultra-crisp, either way. Actually, the harder you’re pedalling, the more crisp that shift feels.

It’s quite nice not to have to think about shifting. I was surprised at how quickly my brain adapted to relying on the auto-shift function. Very quickly I forgot I was still the author of my own destiny, forgetting to shift in anticipation of steeper sections. It caught me out a few times, but I soon re-adapted.

sram gx eagle t-type transmission first ride review
Shifting of Transmission with Powertrain is executed in the very same way as the shifting of Transmission on a regular mountain bike. Credit: Finlay Anderson.

Where Powertrain X Transmission Falls Short

For me, the system is let down by its limited shift speed. This is more in relation to Transmission than it is the Eagle Powertrain and its Auto-Shift function, of course. When it shifts, the T-Type derailleur guides the chain onto the next sprocket of the cassette, ensuring it is properly engaged before initiating a second shift.

You can demand multiple shifts of course, and the system will execute on that, but it will still only shift the chain up or down the cassette one sprocket at a time. The benefit of that is a reduced risk of snapping the chain, of course, but it does mean the system is occasionally too slow to react to dramatic changes in gradient.

This resulted in too many forced dismounts for my liking. The natural trails around Andalo are littered with surprise inclines, and I simply wasn’t able to change gear in time.

sram powertrain coast shifts to select appropriate gear as speed changes
Pedaling out of a corner, I find the system has coast-shifted to an appropriate ratio so that there’s always something to push against. Credit: Mirror Media – Mountain Bike Connection, Summer.

Coast-Shift is Excellent

I found the Coast-Shift function to be excellent. As you coast into a descent and speed picks up, the system auto-shifts to a harder gear so that the gear ratio better matches your speed. That means when you do finally pedal, you have something to push against. There’s less risk of “pedalling into nothing”, and the inevitable maximum effort push-up that follows.

This is not a trap I ever fall into when riding a regular bike. But, it is a trap I fall into when riding other eBikes. I have a tendency to forget which gear I’m in, likely because gear selection seems less important when the motor is going to help you out regardless. The Coast-Shift function is the solution to that problem.

It works in the other direction, too. As you slowly come to a stop, the system shifts back up the cassette so that you’re in a more suitable gear for pedaling off again.

Coast-Shift works by rotating the chainring independently of the cranks. So, if you look down as you coast along, you’ll see the chainring rotating forwards to pull the chain through for a shift. It’s pretty cool.

sram eagle powertrain first ride review chain guide extended
Because the chainring is able to spin independently to the cranks, manufacturers have to spec an over-sized chain guide to prevent injury. Credit: Rupert Fowler – Mountain Bike Connection, Summer.

There is a noise associated with this. The first few times it happened, I thought I had a stick caught in the derailleur because of the noise. I guess there is less torque involved, so shifting sounds less crisp than it does when the chain is under more load.

The Powertrain’s high-resolution speed sensor likely has a lot to do with the efficiency of the Coast-Shift function. Instead of taking a speed measurement once per wheel revolution, it takes a measurement 6 times per revolution. That’s because there are 6 magnets on the disc rotor adapter that forms part of the speed sensor hardware.

Push Mode

The SRAM Powertrain offers a third mode that delivers assistance while you’re pushing, up to a maximum speed of 6 km/h. I ended up testing this feature quite a bit, thanks to the surprise super steep sections.

To initiate it, you have to press and hold the top left Pod Controller button. To engage it, you either start pushing the bike forward, or you can roll it back a little. The motor will engage to prevent the bike rolling back further. That’s a pretty nice safety feature, especially when you are forced to make a last minute dismount on a steep climb. You don’t need to roll the bike back far for it to engage. That’s thanks to the six magnets that are used for the speed sensor.

developing sram powertrain speed sensor 6 magnets hi-res
The system’s sensitivity is improved by a high-resolution speed sensor that takes a speed measurement 6 times per wheel revolution. Credit: SRAM.

I will say, it was pretty easy to accidentally release the Pod Controller button, disengaging Push Mode. That was a bit of a pain, as I then had to wait a bit for it to re-engage. Due to regulations, you can’t change which button is used for Push Mode. You can remove it entirely, though.

If you have the dexterity, you can actually shift while using Push Mode (we did not test this). Theoretically, you should be able to find the right gear sooner, ready for when you get back on the bike.

SRAM Eagle Powertrain | In Summary

Pros

  • Power delivery is smooth, controlled and highly adjustable
  • Cockpit is clean and clutter-free
  • Auto-Shift is impressive and reliable over terrain where gradient does not change dramatically
  • Coast-Shift ensures you’re always in a sensible gear
  • Auto-Shift can be over-ridden at any time
  • Auto-Shift and Coast-Shift are optional

Cons

  • Easy to accidentally release Pod Controller button when using Push Mode
  • Transmission isn’t able to shift fast enough when gradient tips up sharply

Availability

The SRAM Eagle Powertrain is winging its way onto the market very soon. More details to follow!

yannick pontal= wins ews-e 2022 on sram powertrain
Last but certainly not least, it’s worth mentioning that Yannick Pontal won the 2022 EWS-E season aboard an eMTB equipped with an earlier version of the SRAM Eagle Powertrain system announced today. Credit: SRAM.

sram.com

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19 Comments
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King County
King County
7 months ago

A system like this seems amazing, and for the proper demographic it can be a life changer, but to me it has no relation to how I would have defined an ‘adult’ bicycles when I started out, which is simple transportation that is easy to repair, relatively lightweight, affordable, and used 100% under my own power.
This is not a put-down. I am just pointing out how far things have come.

Evan
Evan
7 months ago

600w+ assist! This is absolutely a motorcycle and should require a license and separate trails.

There’s no “oh but I’m old and feeble but still like bicycles” argument here because no one alive needs to ride at 600w just to enjoy bicycles.

Leo
Leo
7 months ago
Reply to  Evan

680 W is peak power, the normalized power is 250 W as every assist on the market (Bosch, Shimano, Yamaha…). For comparison, the Bosch Performance CX and Shimano EP801 peak at 600 W.

Mathias
Mathias
7 months ago
Reply to  Leo

Many people take off power/ speed limits from their e-bikes and Shimano calls such practice “tampering e-bicycles” and Shimano works together with Police to track and tame such cheating.

Jose
Jose
7 months ago
Reply to  Evan

A 50cc gasoline powered motorcycle is about 20,000 watts nominal. No comparison to an eMTB motor.

kevin
kevin
7 months ago

sweet, the already were handling the pedaling, now the shifting. When AI starts clicking they can put an inflatable on the seat and I can keep my fat butt on the sofa.

KGR
KGR
7 months ago

It looks like they chose two ride modes instead of the usual three to accommodate the limitations of the AXS remote.

WhateverBikes
7 months ago

You forgot a Con: It makes what used to be a fun, affordable, light, easy and cheap to maintain, elegant machine into a convoluted, heavy, expensive mess.
Such a shame.

Gabe
Gabe
7 months ago
Reply to  WhateverBikes

It doesn’t replace the fun of your current bike. And it isn’t for everyone. Sh1t, I ride mostly single speed hardtails. I can argue that gears and full suspension take away the fun. They don’t. They offer options. This is a luxurious OPTION that many people will enjoy. Let’s go ride some bikes, people!

WhateverBikes
7 months ago
Reply to  Gabe

‘You can just keep riding a normal bike’ and ‘but it’s so nice for older people’ is what you always hear.
But that’s a bit short sighted.

In reality, nowadays, and more and more so, ebikes are ridden by every age, even kids. Because of that, what is considered a ‘normal bike’ is rapidly changing. It’s not a luxury anymore, it is quickly becoming the default option.
And that means that everything that makes bicycles so awesome, is all being thrown away, all for a bit of assist. And that hurts everybody in the end.

Normal bikes will become a niche product, development is fully focussed on ebikes (range, torque, connectivity and all that), parts will be harder to find, and so on and so on.

blahblahblah
blahblahblah
7 months ago

next

Deputy Dawg
Deputy Dawg
7 months ago

no rattle while descending”

Well, that’s a winner.

Two speeds seems one too few.

Range power level minimum setting needs to be lower, so you can actually use it on long, long days.

benito
benito
7 months ago

Doesn’t this make you wonder, why have other motorbikes not gravitated toward automatic transmissions? Even if you’re an eBike fan, I’m not sure this kind of thing actually addresses an existing need.

Dirt McGirt
Dirt McGirt
7 months ago

I’m super disappointed in this. Another Brose system. The 2nd most inarticulate, clunky and short-lived mid drive on the planet aside from Bafang.

Y A W N

paquo
paquo
7 months ago

lost me at brose motor, what a shame

Justin
7 months ago

I have a “situational awareness waiver” that I make people sign when they drop off an electric bike for repair at my shop. It basically says, “Any bike with a motor is a motorbike”.

Gav
Gav
7 months ago

E-bike haters – jeeze we get it jog on. You’re the second coming of the burned Armstrong fans ‘all roadies are dopers’. Just a tired trope. Being cool is not joining a movement of disparaging holier than thou grumps. Be happy, that’s what MTB is about.

Mathias
Mathias
7 months ago
Reply to  Gav

With lightweight rims/ tires, and with very good bearings in Your hubs coupled with “floating” chainring (TO KEEP STRAIGHT CHAINLINE ALL THE TIME) gimmicks like e-bikes are not worth the hassle. Unfortunately e-bikes generate huge service costs (frequent replacing motor bearings, motor seals, batteries) so they are welocmed by producers. Shame. We can buy expensive floating chainring cranks together with other expensive stuff but many bikers think that motor “fixes” everything.

Peter Van Puyvelde
Peter Van Puyvelde
6 months ago

If they could integrate this concept in a light wheight Scott lumen or so, would be perfect.

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