I don’t like SRAM AXS. The only “problem” it solved was to eliminate a cable, and in doing so it added a battery that needs to be charged and electrical bits that I can’t fix.

It doesn’t shift better, it’s not much easier to set up, and it’s not more durable. It’s also way more expensive. Some will disagree, but I don’t feel that it brought a single performance benefit to the table.

One of the first things I learned about SRAM’s new drivetrain, Transmission, is that it’s only electronic, and I’ve got to admit, that immediately turned me off. But then SRAM sent us their new X0 groupset, and I started to realize that this isn’t just another meaningless update to get us to spend more money.

Yes, it’s still a derailleur, but there are actual performance improvements this time. And now that I’ve spent time on it, the indisputable fact of the matter is that SRAM Transmission is the best derailleur that I’ve ever used.

SRAM’s new Transmission X0 drivetrain.

More precise shifting through stiffness

Transmission brings with it a cosmic shift in how derailleurs operate, the omission of a part that has been integral to bicycle drivetrains since aluminum frames became popular in the 80’s.

You know what I’m talking about, it’s that dangly little bit of aluminum that hangs off the back of your bike: the replaceable derailleur hanger. Like Shimano did way back in 2003, SRAM has introduced a derailleur that mounts directly to the frame.

The direct mount drivetrain that Shimano released in 2003.

Unlike Shimano, SRAM has primed the entire industry to be ready to work with this derailleur, counting upwards of 600 mountain bikes at this point. How did they do this? Well, the ever-dubious Pinkbike commenters were right—the Universal Derailleur Hanger, or UDH, an open source, license free standard that SRAM launched in 2019, a product meant to make it easy for us to find a cheap, $15 hanger no matter where we were, was actually paving the way for Transmission.

SRAM’s Universal Derailleur Hanger

But that’s okay! Standardizing hangers was long overdue, and SRAM made it happen. And along with that, they addressed the question of whether it “still even needs to be there.” The answer, it seems, is no.

Those early aluminum bikes I mentioned couldn’t just be bent back into shape like their steel predecessors, so the solution was to make the part a replaceable weak point, saving that brittle aluminum frame in the event of a crash. But making a thin, flexible member in a system that needs to move a chain up and down a series of gears in tiny, precise increments . . . well, it was never ideal, and it’s gotten worse as we’ve shoved more and more gears into roughly the same amount of space. 

If you’ve used a 12 speed drivetrain, you know how easily they get out of whack. Sometimes everything seems lined up perfectly, but play in the system throws your shifting off. No matter how sturdy you make your derailleur, it’s still attached to the bike by a thin little hanger.

SRAM has used the now-standardized rear end to create a monumentally stronger, stiffer derailleur, which brings me to the biggest positive of the new Transmission: it shifts like the purported dream that their marketing team has described it as.

Does it actually stand up to abuse better? Well, we’re going to try and answer that question, but first let's check out what else they’ve changed.

The X0 model direct mount Transmission derailleur is fully wireless (and hangerless)!

Finally, fully rebuildable

A lot of you are wondering, without that sacrificial piece, what is gonna break? The truth of the matter is that most of the time you hit your derailleur hard enough to bend or break the hanger, the derailleur is toast too. Especially with 12 speed stuff, these components don’t tolerate even the slightest bend in your derailleur, turning it into expensive trash.

But now, like the new Charger 3 damper, Transmission is entirely rebuildable. It can be broken down into 6 different parts, from the pulley cage to the bash plates, all of which are replaceable. That means that if you do mangle something, you’re only replacing one part instead of the entire assembly. And, now you don’t have to go out and track down a hard-to-find hanger along with it. This is huge. It’s always frustrated me to no end how many components are essentially throwaway parts, and SRAM is clearly working to change that, at least on their high end components.

The Transmission derailleur breaks down into different parts that can be purchased individually.

Electric = simpler?

Like I mentioned earlier, this system is electronic. That actually brings with it some benefits besides a cleaner cockpit. It rids us of the need for limit screws, since the range of movement is limited by the gearbox and servo-motor in the derailleur. In fact, the current AXS models don’t need to have their limit screws, but SRAM felt it would be too drastic a change to remove them so soon.

The Set-Up Key replaces the B-tension screw on a normal derailleur. Note the lack of limit screws as well.

With the design of Transmission there’s no B-tension screw to adjust either. There’s simply two positions on this “set-up key” that dictates the gap between the chain and cassette. You can find which one your bike needs on the AXS app or on SRAM’s website.

A different take on a shifter

On the handlebar end, SRAM has gone completely back to the drawing board. With AXS, they tried to keep the form of a mechanical shifter, but in my opinion they somehow managed to make it worse. They’re calling the new, ambidextrous remote a “pod,” because of its looks. Honestly, I think they’ve done a great job with it.

The new Pod controller is wildly different than any shifter that has come before it.

Using their “infinity clamp,” also named after its shape, you can position this thing in a huge number of different orientations.There is also an aftermarket “Matchmaker” compatible clamp available, so you can mount it to your SRAM brake clamp. I could never get the old AXS remote somewhere it didn’t occasionally rub against my thumb, but with this, that’s not a problem. The buttons themselves are large, grippy, easy to press, and can be set up with either convex or concave rubber pads, depending on your preference. If you aren’t into this new pod for some reason, the old AXS remote is the only part of this whole system that is forwards compatible, so you could opt to run that without issue.

Cassette/Chain/Crank

SRAM has made a big deal about shifting under load with Transmission, and they are not exaggerating their claims. This is largely due to the new cassettes, which sit 2.5mm further outboard than the old ones (and are not compatible with regular Eagle drivetrains), are significantly different from Eagle cassettes.

They still use an XD driver, and go from 10 to 52 teeth, but that’s about the only similarity. The new cassettes address a complaint a lot of people had about the gear spread. The jumps in the four easiest gears are now more even, going from 32 teeth to 38 and then 44 teeth before jumping up to the last 52 tooth cog, instead of the old 32 to 36 to 42 to 52 teeth jumps.

Note the greater number of shift ramps on the new X0 cassette (right) versus a typical Eagle cassette (left).

The construction of the cassettes also differs. Instead of gears 2-12 being machined from the same piece of steel, the new cassettes use that X-Dome manufacturing process for the smallest eight gears, then have two stamped steel cogs, and a final aluminum 1st cog. Why did they completely change the construction? I imagine it had something to do with all the new ramps they’ve added to the cogs, and the manufacturing processes required to make them. From the narrow/wide teeth they’ve added to the smallest cog, to dramatically more (and much more intricate) ramps they’ve added to every single cog, there is a whole lot going on.

You can see the narrow/wide teeth of the 12th (smallest) cog, a new addition to the Transmission cassette.

The way these ramps interact with the new chain is the secret to how this system shifts under load so well. Speaking of the chain, that’s new as well, and now has the distinctive “flat top” look. SRAM alleges that it’s the strongest chain they’ve ever made, although they also specify that the new quick-links are definitely not supposed to be re-used due to a concern over the pins shearing off.

The cranks we received are the gorgeous aluminum X0 model, which now use 8 bolts to mount the chainring. That’s what SRAM uses for their Quark power meters, which is at least part of the reason they’ve made the switch. I suspect those extra points of attachment help strengthen things for these new integrated bash guards as well. All in all, a pretty slick setup.

The new aluminum alloy cranks on the X0 drivetrain are a thing of beauty.

Tiers - X0, XX, and XXsl

These components are available in three tiers, including the X0 model I’ve been using, and XX model that features carbon cranks and a few more aluminum bits in the derailleur versus steel parts on the X0 model. That chain also has hollow pins. There’s a new XX SL groupo that has even more weight saving features, like cutouts on the outer links of the chain and a carbon plate on the pulley cage. It also has a fancy lower pulley that can spin even with a stick in it, something that might fall under the category of fixing a problem that doesn’t exist. That said, if you’re racing cross country, those seconds lost from removing a stick could be the difference between a win and a loss.

From top to bottom: The SRAM Transmission X0, XX, and XX SL group sets.

An important distinction between these tiers and normal SRAM Eagle is that X0 and XX are no longer aimed at specific styles of biking, as they used to be. Now they simply hit different price points, with more money giving you lower weights. The exception to this is the SL (Super Light) XX groupo, which is designed specifically to be as light as possible and specifically used in cross-country applications. If you’re riding harder and want weight savings, the carbon fiber and aluminum parts on the XX model are a better choice than the XX SL option.

Shifting: How does it compare?

What really makes Transmission shine is how you can just keep putting down power as you move through the gears, a feature that comes about because of all the new ramps that SRAM’s engineers have added to the cassette, and how they interact with the chain. They call this technology “cassette mapping,” and it’s a series of points around each cog where the chain encounters a little ridge that help bump it up or down the cassette. The additional stiffness of the direct mount system is a necessity to allow you to maintain your power output to move through your gears. All that extra torque being put through this drivetrain wouldn’t fly with the amount of flex that is inevitable with a hanger.

SRAM Transmission shifts like an absolute dream.

There’s no doubt that e-bikes and the significant torque their motor puts down was part of SRAM’s consideration in the development of this design, but it benefits all of us. You literally do not have to make any considerations about when you’re shifting or how hard you’re pedaling anymore—you just shift. You can even dump a bunch of gears at once and keep on spinning; the chain waits until it hits the appropriate ramps on the next cog above or below before moving. 

One of the things I did not like about AXS was that it lacks the feedback a mechanical shifter has, and as a result I found that my shifting performance actually decreased. I could no longer feel, through my thumb, when the chain was catching on the next cog up and before pushing it all the way. I experienced clunkier, louder shifts, and I wouldn’t be surprised if it negatively affected the lifespan of my chain and cassette. With Transmission, that’s simply not an issue. You click the button, and off it goes.

Ergonomics: How does it compare?

Maybe because it’s what I’ve used for 25 years, but I still like the feel of SRAM’s mechanical shifter the best. The feel of the internal mechanism ratcheting, the physical connection to the derailleur; it’s what I like. With AXS, I think SRAM made a misstep when trying to recreate those ergonomics with the remote. There was no reason for it to look the same as a normal shifter, since the design constraints were entirely different. And as far as my hands are concerned, I simply couldn’t get it in a good spot. It was either extremely far away, or so close that my thumb would rub on it when I was descending. I ended up using a left-hand Matchmaker piece to move it slightly further left than otherwise possible, which made it tolerable.

The new Pod controller gives you plenty of opportunity to locate it exactly where you want it.

With Transmission, SRAM has revisited the drawing board entirely. The new remote, called a “pod,” looks entirely different than anything else out there. The “Infinity clamp” that it comes with gives you a good amount of leeway when deciding where to place it, and if you run SRAM brakes, you can get even more with the aftermarket Matchmaker clamp. I actually found the ergonomics of the pod to be much more intuitive than the AXS remote; it comes set up operate the same way a mechanical shifter would, with the lower button moving the chain to easier gears, and the upper button moving it to harder ones. If you want to run it the other way, you can set it to do so on SRAM’s app. And, because SRAM’s electronic remotes are backwards and forwards compatible, you can still run the AXS remote if you decide you like it better.

Durability

A big concern we’ve heard about Transmission is that without a sacrificial derailleur hanger, it seems that either the derailleur itself or even the frame it is now mounted to will be the parts to break. My rebuttal to that is that with SRAM and Shimano 12 speed drivetrains, a significant portion of impacts that would bend your hanger would also bend your derailleur’s pulley cage, rendering the derailleur itself a $400 plus piece of trash (at least in the case of AXS derailleurs). With Transmission, SRAM has not only strengthened the derailleur and tucked it further out of the way of harm —it sits more inline to the bike and doesn’t jut out as far—but they’ve also made the individual parts that make up the derailleur, of which there’s six, replaceable. As we found in the video below, what ends up happening under a severe impact is that a small, easily replaceable part of the derailleur will break. 

Dan’s Take

As I see it, a system that functions significantly better and is repairable is far more preferable than one whose performance is inherently limited by a piece of vestigial technology (the hanger) and that, once broken, is trash. Although I have qualms about putting a battery on something that doesn’t need it, with Transmission’s application it comes with real benefits: the elimination of the b-tension and limit screws, and the set-up that they necessitate. This drivetrain brings with it real, tangible performance benefits; much more so than AXS did. It shifts better while you pedal, something that significantly benefits e-mountain bikers, but also mountain bikers working under their own efforts.

Along with the very slick new cassette, chain, and cranks that compose this drivetrain, I think Transmission is a truly impressive piece of technology, and one that advances the quality of the mountain biking experience. With everything so good these days, there aren’t many product releases I say that about. If your bike is UDH compatible, and if you choose to upgrade to Transmission, I have a high degree of confidence that you’ll be happy with the decision.

Find yours here:
- X0 groupset
- XX groupset
- XX SL groupset