Less than four months after releasing the all-new XX and X0 Eagle Transmission drivetrain systems, SRAM GX Eagle Transmission makes its debut. The wireless, 12-speed mountain bike drivetrain group brings Transmission tech to a lower price point by $500 with a few design and construction differences. I’ve been testing GX Eagle Transmission on a Yeti SB135 trail bike over the past few weeks and have a lot to share.
- Price: $1,099
- Buy from Jenson USA or Worldwide Cyclery.
SRAM GX Eagle Transmission specs and weights
There are plenty of visual differences between the SRAM X0 Eagle Transmission and GX Eagle Transmission groups, and also some key design and performance differences. Starting at the derailleur, the GX Transmission mech (or should we call it an elec? just kidding, horrible idea) is slightly bulkier than the X0 model with matte gray highlights. SRAM has completely reconfigured the battery position on the GX derailleur, and has made a big improvement in my opinion. Instead of hanging off a cliff, the battery sits on a shelf that appears to be much more secure.
Perhaps related to the battery reconfiguration, the AXS button is moved outboard and the LED indicator is much more prominent and easy to view from any angle. According to my scale, the GX version of the Transmission derailleur doesn’t suffer much of a weight penalty, adding less than 20g to the weight of the X0.
When it comes to the crankset, there’s not much of a weight penalty either, though the look is very different. The GX crank arms feature a wishbone design without a cutout, and a matte gray finish. At launch the cranks will be available in 165, 170, and 175mm lengths.
My test unit came with bash bits pre-installed on the 32T chainring (81.3g for the hardware, not included in the chart below). The bits can be easily removed, and are fitted using little bolt-on bits that look like guitar picks. SRAM smartly covers just the parts of the chainring that are exposed and not protected by the arms.
Most of the weight difference between GX and X0 Transmission groups comes from the cassette. The GX cassette features the same 10-52T range and tooth profile. However, it’s constructed using a split design with gears 9-12 utilizing a “single piece MINI-cluster.” Not only that, the GX cassette comes with a nickel plating that’s said to improve durability, though it clearly comes with a weight penalty too.
| X0 | GX | |
| Cassette | 378.3g | 443g |
| Chain | 262.5g | 262.1g |
| Derailleur | 471.4g | 489.1g |
| Crank (drive side)* | 304.2g | 328.7g |
| Crank (non-drive) | 319.7g | 323.8g |
| Controller | 48.8g | 51.1g |
| TOTAL | 1784.9g | 1897.8g |
There’s no discernible difference in the weight of GX and X0 T-type chains, though they are easy to distinguish — black for X0, silver for GX. SRAM says the GX chain features a nickel coating like the cassette. And the GX shifting pod is very similar to the X0 version as well, though SRAM notes the GX controller is the “standard” and not Ultimate model.
It’s been said that Eagle Transmission derailleurs appear big and bulky, and that was certainly the reaction from most friends the first time they saw the GX version in person. According to SRAM, that’s very much by design, with the look of Transmission components meant to communicate robustness and strength.
Installing GX Eagle Transmission
If you own a bike with a SRAM drivetrain manufactured sometime over the past 10+ years, you likely already have all the tools you need to install the GX Eagle Transmission drivetrain. The latest and greatest goes together with an XD cassette tool, and I had no issues using a standard chain whip and chain breaker to complete the process.
It’s clear that SRAM is preparing for a future when consumers might not have access to a local bike shop for installing parts and making repairs. For some, that future may be today, and I found the Eagle Transmission installation process to feel very “appy” and consumer-friendly despite not having access to guidance from the official SRAM app. (The app was not set up to recognize the pre-release GX group I tested.)
Certainly part of the appi-ness is due to the fact that this is an electronic shifting system whose operation is just as much dictated by software as it is hardware. There are no adjustment screws (thank goodness!) and the whole system, literally from the bike frame up, has been designed to eliminate any sort of ambiguity or tolerance mismatches. It’s a very consumer-forward approach that not surprisingly rubs some DIY purists, used to endless tinkering, the wrong way. But I suspect most consumers will appreciate how much guesswork Transmission takes out of the process.
It’s not just the online documentation, or the app, or the fact that little motors just make everything work; setup is built into the product. There’s a red spacer on the cassette SRAM calls the setup cog that helps during installation, and then it just sits there… forever, I suppose. I felt self conscious about it initially, sure that at any moment someone would call out the dork riding around with his setup ring showing. It certainly looks odd, and makes cleaning that part of the cassette slightly more tedious.
I needed to de-install the X0 Eagle Transmission group on my Yeti SB135 test bike before installing GX, and I was shocked by how difficult it was to remove the cassette, cranks, and derailleur. What I assumed was the work of an overly strong and ambitious assembly tech turned out to be a requirement for SRAM Transmission: high torque values pretty much everywhere.
Comparing GX to X0 Transmission
- Price: $500 lower than X0.
- Weight: 112.9g more than X0.
- Nickel-plated chain and cassette
- Battery compartment rotated 90° for better security
- Standard controller but can be upgraded to Ultimate
The amount of torque required for the direct-mount derailleur was particularly surprising, and honestly I was worried I would damage the carbon frame. I dutifully went through the assembly instructions and torqued the derailleur an amount that felt “tight enough” without crunching the carbon dropout. But I quickly found the system was losing chain tension between shifts due to the derailleur rotating slightly relative to the frame. SRAM notes in a FAQ document that they increased the torque recommendation for the mounting bolt from 25Nm to 35Nm for this very reason.
Similarly, it seems to be important to have the proper amount of torque on the bike’s thru axle as well. That’s because the thru axle actually threads into the derailleur bolt, rather than the bike’s frame itself.
While troubleshooting my chain tension issue, I also tried making micro adjustments to the derailleur using the wireless controller, and it’s a breeze. Again, there are zero screws to adjust, and the fact that it all works feels a little like magic.
On the trail with GX Eagle Transmission
Mountain bike derailleurs seem to have improved a lot over the years. Or, maybe I’ve just gotten better at babying them on the trail. Rule #1: avoid shifting under load.
One of the selling points for Eagle Transmission is that it shifts well under load. In fact, SRAM notes in their FAQ and installation docs that the system actually shifts better under load than it does, say, hanging in a repair stand. I’ve certainly found that to be true, and during my tests GX bailed me out of some late shifts on more than one occasion. There’s no sickening cracking or grinding noise shifting halfway up the hill, just a nice continuous shift that’s surprisingly smooth.
Just don’t wait too long to shift. Like the other Eagle Transmission systems, GX Eagle Transmission can only shift up or down one gear at a time; one click, one shift. Reading the documentation, it seems SRAM is prioritizing shifting under load over faster shifts, with the cassette tooth profile dictating its one-gear-at-a-time operation. Still, I think it might be interesting to have a long press shift two gears in succession, even if it’s not instant and the derailleur and cassette have to cycle through the gears one at a time. At the very least it would allow the rider to get their thumb back on the bars more quickly.
Upon further reflection, allowing just one shift at a time, is in a way, ensuring that riders go easy on the derailleur. With a mechanical system riders can press their luck and jump a bunch of gears at once, but there’s always a risk that things could get jammed up catastrophically. Single shifts are certainly less risky and less likely to cause a major malfunction.
Aside from the whirring shift sounds, the GX Transmission drivetrain is whisper quiet and smooth when pedaling and even while descending chunky trails. Clutched derailleurs, along with padded chainstays, have gone a long way toward eliminating most of the sound from MTB drivetrains, but now I realize that there was probably a little bit of sound and/or feedback coming from the jiggly derailleur hanging off the back end of my bike. With the derailleur solidly locked to the frame everything is even smoother.
Strength and durability
OK, back to my rules for avoiding drivetrain disasters. Rule #2: stay to the left side of the trail. Riding in the backcountry and on minimally maintained trails risks snagging a derailleur on a vine or bashing it against a rock. Over my lifetime I’ve easily run into related issues a dozen times or more. GX Eagle Transmission promises a much stronger system, and in my limited testing it’s proven to be extremely robust. I’ve tried kicking it from the side with my foot, and riding through tall grass that would normally choke a cassette, all without causing any problems.
As much as I hate replacing a bent derailleur hanger, I have to admit hangers have saved me on many occasions. SRAM says that according to their research, 50% of bicycle shifting problems are due to the derailleur hanger. Hangers suck because they’re finicky, and weak (by design), and finding the right one for your frame can be a real hassle. Like a lot of riders, I’ve wondered why no one designed a super strong, rigid hanger that wouldn’t bend or break, and what might happen if one did such a thing. Well in a way, we’re all about to find out. So far, it seems the world hasn’t ended, and both derailleur and frame remain in tact.
I decided to do a few bench tests to see how the GX Transmission derailleur would handle some of my usual trail foes: sticks and thick vines. For the stick test, I started with toothpick size and worked my way up to cigar size. The GX Transmission cassette and chain chewed through the smaller sticks with ease and the derailleur didn’t miss a beat.
On the cigar-sized sticks, I managed to get the drivetrain properly jammed up, though again the derailleur didn’t move an inch. Since this was a bench test I wasn’t able to put the full force of a weighted pedal stroke into the drivetrain — just an arm’s worth — so I can’t say for sure what might happen in a real world scenario. In two of the tests the chain actually skipped down past the smallest cog, as shown in the video above, and simply spun which presumably would have saved the derailleur (though it did leave some scratches).
The vine test had a similar result, with a clog of vegetation ejecting the chain outboard and allowing it to spin freely of the cogs and derailleur. I get sticks and vines sucked into my drivetrain a lot, and I don’t ever recall the chain simply re-routing itself in this way. It’s hard to say what’s going on here but my early hypothesis is it’s the cassette ramping, along with the rigid derailleur connection, that makes this work.
Controller
I really like the Transmission controller pod compared to the AXS version, though Matt disagrees so take my opinion with a grain of salt. I still get confused by the AXS controller, I suspect in part because it feels so shifter-like and my brain expects a shifter to work a certain way. With the controller pod, Transmission sorta blows up the old model and provides a controller that’s based around electronic shifting from the start.
The two separate, large buttons are easy to find with a thumb, and the pads are a nice generous size. Whereas AXS uses a hard plastic rocker to shift up and down, the GX Transmission controller features thick, physical rubber buttons that click down with enough tactile feedback to let you know you’ve pressed them. The pod looks strange for sure, and while I’m personally not sold on the looks, it works great in my opinion.
I mostly stopped running bash guards when I made the transition to a single chainring many years ago, though the SRAM Transmission take on a bash guard has grown on me. The guard integrates nicely and as a way to protect your chain ring investment, it’s an easy choice. The composite material rolls nicely over logs and otherwise stays out of the way.
Battery
In a recent survey about electronic drivetrain adoption, a couple commenters noted they don’t like the idea of worrying about charging a battery. After rolling out for a ride and finding my GX Transmission derailleur battery completely deadzo, I have to concur. (Fortunately I had a charged spare sitting on the shelf.)
Like SRAM’s other electronic derailleurs, the GX Transmission derailleur has an LED bulb that glows green every time you shift. The light is said to turn yellow when your battery is low, and red when it’s dead or unable to shift for another reason. It seems the solution to the battery problem is to keep an eye on your derailleur, which IMO isn’t great. Personally I’ll just have to update my ABC ride checklist (air, brakes, chain) to include D for derailleur (battery).
Pros and cons of SRAM GX Eagle Transmission drivetrain
Pros
- Rock solid and consistent shifting
- Easy to install and configure
- Robust design promises long-term durability
- Priced $500 less than X0, and just slightly higher than GX AXS
Cons
- Still much pricier than a mechanical GX drivetrain group
- Requires learning new installation process and remembering to charge a battery
- Non-zero risk of frame damage if the derailleur is impacted. Then again, you’re much more likely to damage your frame by hitting it directly
- Setup ring is ugly and useless after installation
Bottom line
It’s clear that SRAM is staking a lot on the Eagle Transmission drivetrain, and with the launch of a GX-level group they’re clearly targeting wide adoption. In some ways, GX Eagle Transmission outshines the more expensive X0 group, making it an excellent choice for most mountain bikers across a wide range of disciplines. I’m convinced wireless shifting is the future for mid- to high-end bikes, and Transmission sets the bar for what a reliable, easy-to-use modern drivetrain should look like.
- Price: $1,099
- Buy from Jenson USA or Worldwide Cyclery.
