SRAM Eagle AXS Wireless Mountain Bike Group - Complete Tech Overview (2023)

During last year's XC World Cup season, the all-new SRAM Eagle AXS mountain bike group was unveiled. It's the first dedicated electronic mountain bike group with wireless shifting, and it borrows the battery from the road eTap group, but that's about it.

“We don't just put road groups on mountain bikes,” says product manager Chris Hilton. "We also don't just put a motor on the mechanical version. It's bigger, stronger, and less likely to be destroyed if you break it. Physically, the parallelogram's pivots are reinforced, and they have to Growth to make room for the motion system. And that motor and transmission are different than in the road eTap transmission."

All non-electrical parts are preserved. This means that if you already have an Eagle kit on your bike, you can add AXS shifters and derailleurs and it will work flawlessly. The chain, cassette, crank and chainring are all the same. The new XO1 and XX1 parts match the new set, but they are only cosmetic changes (black/polar for XO1, titanium nitride "rainbow" for XX1). The only real difference between the two groups is the material, which we've outlinedin this article

Well, so how are they different?

SRAM Eagle AXS Development and Prototyping

Prototyping proceeds in clockwise order, starting with the unit in the red tray.

First, it's not an Eagle eTap. The "eTap" is for the road group and basically converts the Double Tap shifting mechanism into an electronic click. Like the rest of the entire Cordless Drive line, these receive only the AXS (pronounced "access") moniker to differentiate them from the mechanical offerings. You'll still find hierarchies in AXS, starting at the XX1 and X01 levels shown here.

Now, about that derailleur. It's completely different, with some changes to the obvious electronic/wireless features, but also others to improve overall shifting and drivetrain performance. Starting with the electronics, its body had to grow to accommodate the brains and gear box, with the battery protruding from the back. Although it is never disassembled, the entire mechatronic system is a closed unit protected by a metal exoskeleton.

They started installing windows on the prototype so they could see how the gear was wearing without having to completely disassemble it.

Inside is a motor that spins at about 80,000 rpm. So the gearbox reduces the speed, converting it from speed to torque. There are a lot of gears in there, which is necessary to handle the changing load when changing gears. When you use a larger gear, the torque requirement increases as it works against the greater spring tension of the pulley carriage. So while the gearbox doesn't actually change those gears, it's designed to change the mechanical advantage ratio of the flywheel as you move it up and down.

The clutch is housed in a plastic housing, to the right of the visible springs that protect the internal gears from bump shocks.

There is a clutch between the gear set and the drive arm that allows the parallelogram to disengage safely in the event of a crash. The clutch disconnects the gear from the arm for a second, and then the derailleur automatically returns to its original position so you can continue riding. We'll be posting a video showing it in action in a separate post, so stay tuned.

The "brain" has an entire shift table inside, so it knows where it is in space and how much it needs to move to produce the shift. It's adjusted with a little trim button on the shifter, and once you've trimmed it to a gear position, it lines up perfectly with all gears because the trim moves the entire shifter.

So, technically speaking, the derailleur limit screw is unnecessary. The derailleur itself knows where it is, but they're there anyway as a safety precaution in case you damage it so it doesn't throw the cage over the spokes.

The cage clutch configuration is slightly different than previous mechanical derailleurs, but they will eventually adopt the new configuration on the mechanical unit as well. It'll be called the Type 3.1 because it's a slight reconfiguration of the Type 3, except they won't really be making changes to the clutch anymore, but will quietly put it into production as they find ways to improve it. They didn't borrow a new hydraulic clutch from the road group because this version is more powerful and better suited for mountain bikes... for now.

The derailleur geometry has changed, moving the upper pulley forward and up. The actual cage length is the same, but this change in position also has the effect of raising the lower sheave. The key is to get ground clearance (about 10mm better at the bottom) while also increasing the amount of chain wrap on the cassette. It also positions the entire derailleur mechanism further forward and under the chainstays. It's more protected here, and can actually allow slightly shorter chains in some cases.

From a performance standpoint, increased chain wrap means more precise shifting and engagement, even when you have lots of contaminants (mud, grass, etc.). It's also more precise because the upper pulley is better able to guide the chain between the bottom cogs without giving up engagement with the top of the cassette.

More wrap also means less wear, since more teeth on the flywheel can spread the load over more teeth at any given time. Therefore, each tooth is subjected to slightly less load and wears slightly less. The same goes for the chain, so you should see an overall improvement in component life.

Fun fact: the inner pulley cage plate is compatible with mechanical rear derailleur plates, so in a pinch you can steal parts from your old bike or derailleur...or just order an inexpensive replacement plate from SRAM (via local bike shop, of course).

Eagle AXS Wireless Shifter

In contrast, the transmission is relatively simple. The wireless transmission protocol was developed when the original eTap was introduced, plus ANT+ and Bluetooth, which use the same communication standards as the new AXS road eTap components. Notably, this means that all AXS-labeled parts are interchangeable. Want to add a drop bar shifter and brakes to your monster dirt bike with a mountain cassette and rear derailleur? no problem. Want a fast flat-handle bike with a road group? You can do that too. Heck, you can even replace those MTB shifters with Blip Box and Blips buttons and use them to shift your bike. You can customize how all of this works with the AXS application (check out this post to see how it all fits together).

The body houses a CR2032 button battery, transmitter and two switches. The paddle or lever is bolted to it, and the bolt doubles as the pivot point for the paddle to swing up or down. All the paddle needs to do is make contact with the switch to actuate it, which means, technically, it can take any shape they (or you or the bike brand) want. More on that later. First, development.

SRAM tested various button, lever and paddle layouts to see which worked best, but they all basically shared the same mechanism: two switch buttons, one for upshifts and one for downshifts.

They even tried a wireless GripShift-style twist shifter, which actually only requires a small amount of twist. Currently, these won't be available, but don't know what will happen in the future.

Button up, button down. button up...

They land on a smooth rocker panel that extends forward...

...which means you can position the shifter to favor pushing and pulling with the knob on the front, or rest your thumb on the rocker panel at the rear. We'll discuss some other options later in this story.

There are pairing/trim buttons at the bottom of the shifter. Use it to set up the group and pair it with the rear derailleur, then hold it while pushing the shift paddles in either direction to trim the derailleur to fine-tune shifting performance.

The result is a very clean cockpit with only the brake lines visible. So, how does it ride? Read on and we'll get there with links to our first ride review and more AXS content at the bottom of this article.

There is an AXS app that does just that...

We have a full feature story about the AXS system and this app, you can see it in action in the video of the new RED AXS road set, but here is the brief version:

The AXS app, available for iOS and Android, allows you to assign shifts or other functions to specific AXS buttons. Reverse shift mode, or send an upshift to the Reverb AXS remote, then use one of the shifter's "buttons" to put your action down. You can also toggle multishifts on and off. Or never download the app, just install groups and ride. SRAM doesn't want your enjoyment of the group to be app-dependent, but it provides additional features that allow you to customize it to suit your needs.

Another cool feature is the app's ability to display gear usage. The derailleur knows how much time is spent in each gear and syncs that data with the app. Eventually, it might provide alerts or service reminders based on mileage, but at least you can use the data to see if smaller or larger platters improve your efficiency. Other features may come in the future, but rest assured, no one can download the app and use it to control your shifting...it can't change the system, it can only change the button settings. You need to pair the parts with your app, and they can only be paired with one thing at a time... so unless they have your phone, they can't interfere with your system. Finally, you don't have to create an account if you don't care about saving any settings, so you can remain completely anonymous with SRAM if you wish.

other things you should know

The battery lasts for 20 hours and takes just 1 hour to charge. Since it's the same as all other AXS components, you can borrow batteries from your Reverb AXS or road AXS pack in a pinch. Or just take a spare, they're only 25g. You can check battery life by pressing a button on the derailleur. Green means it's ready to use, red means it's about half charged, and flashing red means it's almost dead. However, the shifter's battery should last up to two years of riding.

The kit is waterproof to IP69K standards, which means that even with the occasional pressure wash, you're less likely to harm it (as we all know we do sometimes, and professional mechanics do it a lot). So, rainy days, crossing streams, etc. are no big deal.

The XX1 group now comes in "Rainbow" colors, which are actually a similar titanium nitride finish to the original gold, just not as obnoxious.

While both this chain and the chain from the new road group are 12 speeds, they are sized differently and are not cross compatible.

The aftermarket group will go with a 32-tooth chainring for the XO1 and a 34-tooth chainring for the XX1. All the usual other sizes are still available and the crank onlySpindle with DUB dimensions, so you need a compatible bottom bracket.

SRAM Eagle AXS Hacks and Prototypes

too fast?

Not exactly, no. Throughout the launch, the SRAM team stated very publicly that they were having a hard time deciding on the final button layout for the shifter. Obviously, one of the few difficulties was actually getting all the departments to agree on the AXS name.

They also admit that they fully expect third parties, bike companies, and even regular riders to come up with alternative button arrangements to bolt on to the stock shifting. The pictures above and below were taken on an employee's bike, used as a test mule, who (unofficially, of course) prefers this button layout. Personally, after trying it too.

The rear rocker panel sits further inboard, and the front bump has a more usable paddle for a better grip with your index finger. So, do you have a 3D printer and some skills? Time to start a side hustle...

We also found this battery cover on another bike. They didn't tell us anything about it, but it's held in place very securely, and probably for extra impact protection. It snaps in using a different connection point than the battery itself, so if it does get knocked off, it doesn't seem to take the battery with it.

Want a full AXS pass?

We'll be covering the entire SRAM AXS launch in multiple parts, the rest are as follows:

  • SRAM AXS Overview
  • SRAM Red eTap AXS 12sp Road Group Technical Overview
  • SRAM Red eTap AXS 12sp First Ride Review
  • Rockshox Reverb AXS
  • unboxing! SRAM Eagle AXS Mountain Bike First Impressions

SRAM.com

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