The Wireless Workhorse: SRAM GX Eagle Transmission Tested 14

At the end of March of this year, SRAM dropped its all-new Eagle Transmission platform. Based on wireless AXS technology, Transmission marked another major new milestone in the history of the bicycle drivetrain: the hangerless derailleur interface. SRAM also made wholesale changes to the dimensions of the chain which meant replacing your whole groupset if you wanted to jump aboard the Transmission train – and that did not come cheap. X0 MSRP was set at $1599 USD and XX at a whopping $2049 USD, leaving piggybanks across the world fearing for the lives as early adopters stretched their budgets to lay their hands on the new tech. Today, SRAM introduces GX Eagle Transmission, and while we still wouldn’t exactly call it affordable, the trickle-down has only taken three months and $1099 USD for the full group is pretty good, especially considering how well it works. Keep reading to learn more!

SRAM GX Eagle Transmission Highlights

• T-Type chain compatibility
• Revised derailleur battery position, reconfigured gearbox, replaceable skid plates and outer link, tool-free cage and clutch
• Install and pair via standard AXS set-up and pairing procedure (backwards compatible with AXS controllers, NOT compatible with regular AXS components like chain and chainrings)
• Hangerless Interface, Full Mount attachment method
• Forged aluminum crank (165, 170, and 175 mm length) with an all-new shape and two independently removable composite bashguards (“DUB Wide” spindle = 174 mm Q-factor)
• E-Bike ISIS crank arms available (160, 165, and 170 mm length)
• 30T, 32T, and 34T chain ring options, with 3mm offset for 55mm chainline
• X-SYNC cassette with 520% range and optimized gear steps on low end, 55mm chainline compatibility, “PinDome” design for gears 1-8 and a single piece MINI-CLUSTER for gears 9-12
• Flattop T-Type chain with solid pins
• MSRP (as tested) - GX T-Type Eagle Transmission AXS Groupset (RD w/Battery/Charger/Cord, EC POD, FC GX Q174 DUB MTB Wide 170 Dark Polar w/DM 32t CR w/2 Guards, CN126l, CS XS-1275 10-52t) : $1099 USD
• GX Transmission individual component pricing: Derailleur (excl. battery) $400 USD, Crankset (incl. chainring, excl. BB) $200 USD, 10-52 Cassette $250 USD, Chain $50 USD, Chainring $42 USD, AXS Pod Controller $150/$200 USD, GX Crank Arms for ISIS e-bike $140 USD

Weights

Here's a quick comparison of component weights across the Eagle Transmission line:

Initial Impressions

When Eagle Transmission launched earlier this spring, we produced an in-depth article describing the new architecture and technologies in detail – you can brush up on all that HERE. To summarize, Transmission does away with the traditional derailleur hanger in favor of a direct mount standard that attaches the derailleur directly to the frame at the end of the rear triangle. This is possible because of the relatively widespread adoption of SRAM’s Universal Derailleur Hanger (UDH) standard, introduced a few years ago to help the industry standardize this component to make it easier for users to find replacement hangers when out and about (and ultimately yes, to accept these new direct mount derailleurs). Mounting the derailleur directly to the frame in this way allows SRAM to do away with traditional derailleur limit screws – with the cassette always sitting at exactly the same distance from the derailleur, the system already knows where the cassette begins and ends. Additionally, the direct mount is much stronger than any derailleur hanger could ever be – you’ve probably already seen the pictures and videos of people standing on their Transmission derailleurs to demonstrate just how strong the mount is.

The changes weren’t limited to the hangerless direct mount interface. Transmission also introduced a whole new chain called the T-Type. Easily distinguished by the flat top of one side of the chain, T-Type is slightly different in its dimensions which means that traditional Eagle chains won’t work with Transmission components. The new derailleurs will however work with the previous generation of AXS controllers, which can make upgrading slightly less costly if you have already invested in Eagle AXS.

So what’s new with the GX level Transmission group then? Let’s start with the price tag: we wouldn’t call $1099 USD for the group cheap, but it is a whole lot more affordable than X0 or of course XX (the full mechanical GX Eagle group goes for $587 USD at MSRP, for comparison). Looking at the new GX derailleur, the most visible change is that the battery has moved into the derailleur body, placing it in a much more protected position. The derailleur itself looks a lot sturdier, with bigger “skid plates” and all-around beefier proportions. The derailleur cage is made out of steel, in keeping with the robustness objectives for this new group, but much like on the more expensive X0 and XX groups, the cage and clutch assembly can be swapped out individually to replace a bent cage for example, or to upgrade to a lighter assembly. Other parts of the GX Transmission derailleur can be individually replaced too - it’s nice to see this aspect of the architecture trickle down to the lower price point.

The alloy GX crank looks a lot like the X0 crank, just with less material machined away. It comes with two bash guard plates mounted to the chain ring, and your choice of a 30, 32, or 34 teeth chain ring. The tooth profile is new, with very elaborate shapes meant to mesh perfectly with the new T-Type chain (as previous stated, T-Type components are not backwards compatible with traditional Eagle parts, so moving up to Transmission does require you to swap out most of your existing drivetrain). A change introduced by Transmission that has flown a bit under the radar perhaps is the move to a 55 mm chainline (up from the classic 52). SRAM states that this improves shifting performance and longevity of the cassette. To make room for the new chainline, the crank spindle is now 6 millimeters longer and called “DUB Wide”, which also means that the overall Q-factor moves up from 168 to 174 millimeters. This move also makes room around the BB area of the frame, which could be beneficial to frame manufacturers as they try to fit in their chosen linkage design elements while maintaining shorter chainstays on 29-inch bikes, for example.

Moving onto the cassette, we find the same revised sprocket sizing introduced on XX and X0 Transmission, with more evenly spaced out steps between the top three climbing gears (now 52, 44, 38 compared to 52, 42, 36 on mechanical Eagle). Also featured is SRAM’s “cassette mapping” which is basically an elaborate set of shifting ramps and all kinds of intermingled tooth profiles that dictate where the chain can shift and where it should not. The GX Transmission cassette is built using heavier materials and utilizes a simplified construction with a “mini-cluster” for gears 9-12, which has also allowed SRAM to drop the price significantly. An X0 Transmission cassette will set you back a whopping $400 USD (not to mention the $550 XX version…), but the GX cassette sits at a much more affordable $250 USD. We predict quite a few X0 and XX Transmission owners happily replacing their cassettes with the GX version when that time comes, the weight difference is not all that significant and we have not been able to identify any performance differences in the real world. At just $50 USD the GX T-Type chain is also refreshingly affordable.

Installation

Installing Transmission is easy and in many ways much simpler than installing a classic mechanical drivetrain. To state the obvious, not having to deal with cable routing is wonderful, but that’s not the only difference. The new direct mount interface takes all the guesswork and tedious micro-adjustments out of the process, but you do have to do the steps in order and follow the instructions precisely to get it right. Start by looking up your bike model in the “Chain and Setup Key guide”, which will tell you how many links to remove from the chain, as well as the position required for the “Setup Key” and which setup cog to use. The setup key holds the derailleur cage half-open, in a position that will translate to the correct derailleur position and chain tension later in the process. For our Transition Smuggler, we cut the chain to 116 links and placed the setup key in position B.

After installing the components on the bike (but without fully tightening either the derailleur bolt or the rear axle), you then lock the cage open in the setup position and shift the chain to the prescribed setup cog (the 21t, in the case of our Smuggler). At this point you pull the derailleur backwards until the chain is under tension, and then you lock down the main derailleur bolt and torque it to spec. There are a couple of little markings that need to be aligned at this point – if they are not, repeat the process. Then tighten the rear axle, release the cage lock, and voila – you’re done! We were stoked to nail it on the first try and seeing the system shift flawlessly out of the box was cool. The new “pod” controller integrated nicely with the SRAM brakes on our test bike, and we were able to find a good position for it fairly easily (there is also a version of this controller with a discrete clamp that mounts directly to the handlebar of course).

On The Trail

When we first tested a Transmission drivetrain, we were blown away by how smooth and precise the shifting is. Good news, we feel the same about the new GX version. The “cassette mapping” shifting ramps make sure that the chain only shifts in pre-determined spots, which can take a little getting used to, especially if you’re the kind of rider who likes to “force-feed” your gears with a mechanical derailleur. With Transmission, the derailleur moves when you tell it to, but the chain will only shift to the new cog when it hits the shifting ramp on the cassette. You can shift in rapid succession, but if you click more than two times the system will queue the remaining shifts until the first two have actually shifted. It takes a little getting used to, but it becomes natural enough pretty soon. The real party trick here is that you can shift under load. Realized you’re in the wrong gear in the middle of a steep climb? No problem, just keep pedaling and shift into the desired gear. The shift stays smooth, and the cassette was built to be able to take the power even when the chain is moving between cogs. If you miss being able to shift multiple gears with a single press of the lever like on a mechanical drivetrain, you can configure Multi Shift to shift 2 or 3 gears at a time when holding down the shift button (requires connecting to the SRAM AXS app).

As the trail turned downhill, we noted that GX Transmission runs very quiet - more or less the same level of quiet as the XX Transmission (which some of our testers feel is a fair bit quieter than "regular" AXS derailleurs). We’ve had the system installed on our main test bike for about 3 weeks now (as well as on a second test bike under another tester), and the shifting has remained smooth and precise throughout, regardless of what the trail might have thrown at it. Chain retention has been flawless so far, and we can’t remember any missed or noisy shifts in any situation. At this point, the slight disconnect between the derailleur movement and the actual shifting moment feels for the most part natural, and we don’t really find ourselves thinking about it or having to make any adjustments to how we ride – on the contrary, it’s all pretty intuitive and it’s really a bonus to be able to shift under power. We’re also getting along well with the new “pod” shifter, which in the opinion of all of our testers provides a better ergonomic experience than the original AXS “rocker” shifter.

3 weeks is of course not enough time to draw any conclusions regarding longevity and durability, but GX Transmission feels very sturdy in terms of build quality and we have not identified any potential weaknesses so far – on the contrary, this really seems like a workhorse group, ready to take quite some abuse and keep coming back for more. The hangerless interface is very strong, and the clutch release mechanism that protects the servo motor functions well. As stated early on in this article, we applaud SRAM for making the new Transmission derailleurs modular, allowing riders to swap out individual parts when they get damaged. The only issue we’ve encountered so far is some bug preventing us from connecting the rear derailleur to the SRAM AXS app (we have two GX Transmission drivetrains running right now, and they both exhibit the same issue). Hopefully something that SRAM will resolve for us soon.

What’s The Bottom Line?

$1099 USD isn't chump change and we're not going to suggest that SRAM's new GX Eagle Transmission should be on every mountain biker's radar from here on out. It is however a lot more affordable than either X0 or XX Transmission, and it has kept very nearly all of the features of its higher-end brethren which makes it a great deal in our books. Trickle-down at its best, the new GX group has performed flawlessly in our testing so far, and it is certainly fair to say that it upgrades the user experience compared to a mechanical groupset or even first-gen AXS wireless. Shifting is crisp and clean, and the ability to shift gears under power is a real advantage. Durability has been a key focus area during the design of the new group, and with individually replaceable components the derailleur is a lot more futureproof than we've been used to historically. If you have a UDH-compatible frame and you want to dip your toes in the wireless shifting pool, you should certainly consider GX Eagle Transmission first. X0 and XX have the bling factor and the weight advantage, but in terms of performance, there's nothing in it.

More information at: www.sram.com.

About The Reviewer

Johan Hjord - Age: 50 // Years Riding MTB: 18 // Weight: 190-pounds (87-kg) // Height: 6'0" (1.84m)

Johan loves bikes, which strangely doesn’t make him any better at riding them. After many years spent practicing falling off cliffs with his snowboard, he took up mountain biking in 2005. Ever since, he’s mostly been riding bikes with too much suspension travel to cover up his many flaws as a rider. His 200-pound body weight coupled with unique skill for poor line choice and clumsy landings make him an expert on durability - if parts survive Johan, they’re pretty much okay for anybody. Johan rides flat pedals with a riding style that he describes as "none" (when in actuality he rips!). Having found most trail features to be not to his liking, Johan uses much of his spare time building his own. Johan’s other accomplishments include surviving this far and helping keep the Vital Media Machine’s stoke dial firmly on 11.

Photos by Johan Hjord