After months of leaks, spottings, and speculation, SRAM unveiled their newest wireless mountain groupset, Eagle Transmission, along with a collection of Stealth Brakes. This hefty product launch encompasses derailleurs, cranksets, cassettes, shift controllers, and more across XX SL Eagle, XX Eagle, and XO Eagle levels along with power meter and e-bike-specific components. SRAM also released an all-new Stealth lever body for their Level and Code brake lineup. As such there’s a lot to unpack here, which we expect to dive deeper into during the next few months of Transmission-equipped bike reviews. Today, however, let’s take a look at product highlights and some initial thoughts about these new components after a few rides on a Santa Cruz Megatower test bike that SRAM sent us a couple of weeks ago.
With SRAM’s adoption of the Universal Derailleur Hanger a few years ago, we knew something new was coming. Well, Eagle Transmission is that something. This isn’t just a few tweaks to the existing Eagle AXS, rather, it is an entirely new system with all new parts in—as SRAM describes—a rethinking of “the entire interface between frame, wheel, and drivetrain.” With no derailleur hanger or adjustment screws, the aim of this system is to allow “flawless shifting under maximum power.” That’s right: no separate hanger and no limit screws. Instead, the derailleur is attached directly to the bike frame and tensioned through a straightforward setup method as seen in this video and/or with the assistance of SRAM’s new mobile app which bases tension on a number of factors including bike model, chainstay length, chainring size, etc. To maximize and optimize the capabilities of Transmission, you must outfit your bike with the complete component suite—an ecosystem, if you will—consisting of derailleur, crankset, chainring, chain, and controllers. Should you choose to use just a few parts on their own – like just adding a Transmission derailleur to your existing Eagle AXS drivetrain – SRAM claims that Transmission will not function properly for reasons described below.
These new XX SL, XX, and XO derailleurs are “engineered as integrated, interdependent Transmission components [where] the T-Type [Transmission Type] derailleur mounts around the wheel axle itself, contacting the cassette directly with a first-of-its-kind Hangerless Interface.” This, as SRAM point out, creates a far stronger connection as the mech mounts directly to both sides of the bike frame and the axle.
All three levels feature an integrated overload clutch, which essentially decouples the motorized internals in an impact to prevent damage. There’s also a replaceable B-knuckle cover and outer link. Yes, we’re talking about a partially rebuildable derailleur. This is SRAM’s answer to those of us who may fear that Transmission eliminates the derailleur hanger’s capacity to save the derailleur by “breaking away.” Most modern thru-axle hangers are too strong to break away before the derailleur is damaged anyway, so this may be a way to give the $XXX Transmission derailleur a second or third life. We won’t know how effective it is until we bash our test derailleur hard enough to take advantage of it.
Giving the derailleur such wide purchase on both sides of the dropout helps add durability, but SRAM had no way to quantify exactly how much. What they did have, though, is Nino Schurter. At a World Cup XCO race in August of last year, Schurter slid out in a right-hand turn, and appears to have ground the derailleur into the dirt for a good three feet. It was the sort of crash that wouldn’t necessarily rip off a derailleur, but would likely bump it out of alignment. The rest of the race appeared to be problem-free, since he ended up securing his 10th World Cup title that day.
Additionally, XX SL and XX versions incorporate a two-piece lower pulley called Magic Wheel, which allows the pulley teeth to rotate independently of the pulley “spokes” if an object becomes lodged within them. Without the uncertainty introduced by a potentially misaligned derailleur hanger, Transmission cassettes and derailleurs make direct contact with each other “ensuring perfect alignment on every bike.” The derailleurs also incorporate what SRAM is calling an “Inline Cage,” where the pulley cage doesn’t just stay parallel to the cassette cogs, but instead remains continually oriented to point towards the chainring. So they could be sure they knew exactly where that chairing would be relative to the derailleur, SRAM is also introducing a dedicated Transmission crank.
In a departure from SRAM’s 3-bolt direct-mount crank and chainring system, the new Transmission cranksets feature an 8-bolt interface aligned with “T-Type” compatibility throughout the system. SRAM touts the hollow core carbon fiber XX SL to still be the lightest on the market and the XX crankset features foam core carbon arms with a removable bash guard. SRAM refer to the XO crankset, with a balanced stiffness-to-weight ratio, as “the most advanced aluminum crankset we’ve ever made”; it, too, includes a removable bash guard. New 8-bolt direct mount chainrings are available in four sizes from 32-38T and two offset variants (0 and +3).
Cassettes and Chains
The harder you pedal, the better it shifts. SRAM boasts that Transmission’s design enables riders to shift more efficiently (seamlessly, even) under high pedaling load. A major part of this enhanced rideability comes from T-Type cassette/derailleur interface. Without interference from a traditional derailleur hanger, Transmission cassettes and derailleurs make direct contact with each other “ensuring perfect alignment on every bike.” The new cassettes retain a 520% gear range but have an improved progression ramp with 44 and 38T cogs in the low end as compared to the 42-36T steps in 10-52T Eagle cassettes.
The Transmission cassette sits 2.5mm closer to the dropout than a traditional Eagle cassette in order to work better with the growing number of frames built with wider 55mm chainlines. These nudge the chainring 3mm further outboard than the 52mm chainline normally paired with Boost 148mm hub spacing. That’s just one of a few reasons why Transmission and non-Transmission components can not be mixed and matched. Also, SRAM totally remapped the shift ramps and tooth profiles on the Transmission cassette, aiding both in durability and shifting precision.
T-type cassettes all have a dedicated setup cog for chain placement when configuring the system. As is often the case, material spec and distribution dictate pricing and advertised durability with the lightest weight being the spendiest. Flattop T-Type chains are designed to optimize Transmission performance, offering “shift when you want performance” and are the strongest chains SRAM have ever made.
AXS Shift Pod Controllers
The new AXS Shift Pods are the only component released with Transmission that is backward compatible with Eagle AXS groups. That also means that, if you like the previous styles of AXS shifters, they’ll work fine with a Transmission derailleur. Feature highlights include a two-button “click and fire” design, button command personalization, interchangeable right/left mounting, and lots of adjustability. The deluxe version includes replaceable concave/convex buttons. They are also lighter weight than the previous generation controls.
Designed to appear aesthetically consistent with the new Transmission groupsets, SRAM have also brought the brake hoses closer to handlebars on their 2 and 4-piston Code and Level brake levers. Lever and caliper internals remain the same, with only levers changing in appearance. Like it or not, this design change was probably made with thru-headset cable routing in mind, so we’re likely to see more mountain bikes using it in the future.
Initial Ride Impressions
As I said in the introductory paragraph above, there is a lot to unpack with this Transmission release. SRAM is asking us to reimagine what we know a bicycle drivetrain to be. Are we ready?
On one side of the coin, it’s super exciting. New tech and innovation, more broadly, usually are. Did you watch the install setup video? It looks SO easy, right? After a few rides on the test bike SRAM sent me, a Transmission XO-equipped Megatower, I have to say I’m pretty blown away with how well the system performs over my Eagle AXS drivetrain. Shifting is very precise and super smooth, even while pedaling hard up super steep inclines the chain glides between gears rather than jumps. The ghost shifting and chain slop that occurs so often on first-gen Eagle AXS? It seems to have been nearly eliminated. And the controllers. Wow. I was equally impressed by their comfortable tactile feel and the uber-ergonomic customization options.
Simplifying the system by removing the derailleur hanger and limit screws seems great in theory. But this is one area where we need to spend more time on the trail to see how Transmission performs over many months of hard use. While most of my apprehensions of using a wireless drivetrain on long remote rides have largely been assuaged by the reliability of Eagle AXS, the idea of not having replaceable items in my repair kit (like an extra shift cable and derailleur hanger) still makes me a little uncomfortable.
While SRAM says the brake internals are the same as found in previous generations of Codes and Levels, the Stealth Codes on the Megatower demo felt better than any other SRAM brake I’ve used. Admittedly, I’m a fan of Paul, Hope, and Shimano and have stayed away from SRAM brakes after a few not-so-great rides with subpar modulation/lever return/piston functionality, but my opinion of them has changed after such a positive experience with this Stealth setup. Now, this was only after a few rides, so the verdict is still out on how these would fare over many months/years of use. Additionally, while I think the lever redesign will cater most to internally routed cockpits, it incidentally looks great for attaching handlebar bags.
But, on the other side of the coin, my initial reaction to all of this innovation has been a bit curmudgeonly. Just last week, in his Bicycle Sentences, Grant Peterson of Rivendell captured my sentiments with this line:
“The goal of bicycle technology is to replace levers with buttons, mechanical movements with electronics, tire air with foam and to introduce ‘revolutionary’ technology every few years so you’ll buy new rather than maintain what you’ve got.”
Do bikes even need to be this good? Sure, I was a late adopter of electronic shifting in the first place. I’m only using it because I purchased a pre-owned bike that already had it. But, once I rode it I was hooked. AXS could be improved, but to make it better all SRAM needed to do was update with a better clutch mech and call it good, IMO. But an entirely new proprietary ecosystem already? Transmission seems to be on a completely different level of technological advancement just a few years after the first-gen AXS was released. And Stealth Brakes? Be honest – who is asking for internally routed MTB brake hoses?
To their credit, a representative from SRAM told me they will continue to manufacture/warranty mechanical drivetrains and first-gen Eagle AXS for the foreseeable future. But do we need these completely new systems to come out every few years? Personally, I don’t think so. I’d rather maintain the components I already have and repair/replace single items as needed. Plus, I often prefer to purchase gear piecemeal as I can afford it. While I suspect we’ll initially see Transmission kits on new complete bikes, I like pairing bespoke cranksets with my builds, which isn’t possible with Transmission. And chainrings too, as SRAM’s smallest ring is a 32T, and I rarely run anything bigger than a 28 or 30T. At least until third-party manufacturers adopt the new 8-bolt direct mount standard. Again, context is everything and this is only my opinion – a guy that just built a bike up with 25-year-old XTR 952 and is scrounging for friction shifters.
All retro-grouching aside, I do look forward to seeing our contributing reviewers, including myself, further evaluate Transmission on test bikes in the coming months. It’s an exciting achievement regardless of other philosophical ramifications.
Shoutout to Jeff Olsen for modeling in the action photos!
Transmission groupset pricing is $2199 for XX SL, $2049 for XX, and $1599 for XO. There are additional groupset variations available that incorporate power meters and e-bike-specific components. Parts can also be purchased individually. Head over to SRAM for further details.