The Takeaway: No need to change your cadence or ease up on the pedals: Transmission offers smooth, quiet, and ultra-solid shifting up and down the cassette even under full load. But the biggest benefit is durability and longevity.

• Compatible with any UDH-equipped bikes
• Derailleur pulley cage and outer link are replaceable
• Requires T-Type chain, cassette, and chainring.
• Part of the AXS ecosystem and cross-compatible with many AXS parts
• Three tiers: XX SL, XX, and X0
• New controller pod
• New power meter options

 

Weights:

• Derailleur: 443g
• Controller pod: 48g
• Cassette: 381g
• Crank: 599g (165mm, 32t ring w/bash guards, power meter spindle)
• Chain: TK

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SRAM Transmission

The worst-kept product news in all of the cycling world is finally here. And it’s why SRAM invented the Universal Derailleur Hanger: Its long-anticipated direct-mount mountain bike rear derailleur.

Transmission is the name SRAM bestows on the latest evolution of its 1×12 AXS drivetrain. Technically, Transmission (or T-Type) is an Eagle AXS drivetrain, but in SRAM-speak, Eagle is the existing 1×12 stuff, and Transmission/T-Type is the 1×12 built around a direct mount rear derailleur.

After countless leaks, much speculation, and even a system finding its way to Craigslist, T-Type finally launches today in three flavours: XX SL (lightweight), XX (all-purpose), and X0 (the least expensive variant).

While there are numerous changes, SRAM eases the transition to Transmission by utilising many of its existing standards. Transmission still employs XD cassette mounting, is compatible with Boost 148 rear wheel pacing, the cranks still use Dub axles, they stuck with the familiar MatchMaker X brake lever/shifter mount integration, and the derailleur uses the same battery packs as Eagle AXS.

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Ride Test and Review

As I look back on my anticipation and predictions leading into my first rides on Transmission, the on-trail experiences were a slight letdown. What I wanted and expected was game-changing performance: Revelations and a revolution. Something that behaved so clearly better that I never wanted to ride anything else.

That’s not what experienced. For sure, Transmission shifts very well. It’s extremely smooth, nearly silent, and faultlessly robust. With Transmission, there’s no need to ease up on the pedals or slow your cadence; no need for “shifting technique.” You just shift: Any time, at any power, and as many cogs as you want. It is the best shifting SRAM mountain bike drivetrain ever. No derailleur drivetrain on the planet (from any brand) shifts better under load than Transmission.

Still, I was surprised that for all the new parts and the new derailleur attachment paradigm, the shifting performance is simply more polished than the existing Eagle AXS (which shifts very well), and not radically better. I also think—and my colleague Dan Chabanov agrees—that Transmission shifts a touch slower than Eagle AXS. No, I’m not calling Transmission’s shifting slow, but I’m not calling it fast either: The word that kept coming to mind as I rode was “deliberate.”

I spent most of my time testing Transmission riding in Moab. It never hesitated, never skipped, and hardly made a noise even as I intentionally ham-fisted multiple shifts under full power, up or down the cassette, while pounding my way up or down a trail with my bike’s rear suspension compressing and extending. How little you need to think about shifting when riding Transmission is a gift.

It’s also wonderful not worrying about every rock and stick lingering at derailleur-level. The T-Type rear derailleur is a freaking beast and looks and feels like it’ll survive a nuke strike. So far I’ve only dragged it on a few rocks—I’ve not laid the bike down on the derailleur in a crash or smashed anything yet (oh, but I will)—and stood on the mount for fun. I may eat my words, but I’m predicting this thing will change the game when it comes to durability and longevity. And those are the biggest benefit of Transmission—Smooth-shifting and quiet running are, to me, wonderful side benefits.

For sure, Transmission shifts very well. But the shifting performance is not so over-the-top amazing that I’d run to strip my current drivetrain—be it Shimano mechanical, SRAM Eagle mechanical, or AXS—in favour of Transmission. But when it is time for a new drivetrain—because of wear or damage—I’d absolutely switch to Transmission. Not because of shifting performance, but rather my motivation would be to gain because of the toughness, strength, and crashproof(ish)ness of the T-Type rear derailleur. Plus, it uses rebuildable parts. Seriously, gold star for SRAM for making a rear derailleur with so many replaceable parts.

While the derailleur is the highlight, it’s not the only thing new about Transmission. There are also the new Pods, which I’m not sure about. Even after many hours of riding, they still don’t feel intuitive to me, and I’m struggling to get them into a position that feels natural. I didn’t love the feedback from the buttons either, which I found somewhat vague and rubbery. But since this is AXS, I can run the rocker paddle controller. This is another point to SRAM: No other drivetrain lets the rider choose from so many shifter options.

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The Hard Questions

From the outside, it’s not hard to be annoyed that Transmission is an integrated system and not backward compatible with Eagle AXS components. Why is there a new chain, a new cassette, and a new chainring—Are they really necessary, or is SRAM just exploiting the hype to squeeze more money out of riders?

Maybe the new chain, cassette, and chainring really are necessary to unlock the bestperformance. Even so, a direct mount rear derailleur built for SRAM’s existing 1×12 parts would at least shift as well Eagle AXS—pretty damn good—and wouldn’t obsolete all the great and fully functional parts already in the field: Why not make that?

I posed these questions to SRAM’s Chris Mandell and he pushed back, “We invested a tremendous amount of work to pull off what we pulled off,” he said, stating that SRAM needed to go with full system integration to achieve their goals: Ease of setup, durability, and shifting performance under load. Based on my experience, SRAM made a drivetrain that is incredibly easy to set up (simply size the chain and tighten a few bolts), shifts fantastic under load, and appears extremely robust.

Mandell added, “We used the minimum number of viable parts we needed to make the system work,” before pointing out SRAM didn’t change the requirements for cassette mounting, hub spacing, crank axle, or derailleur battery.

I hoped Transmission would roll out with something cheaper and less complex like the AXS upgrades SRAM offered that allowed riders on Eagle to upgrade to wireless electronic shifting with just two parts: The derailleur and the controller. But, so far, that’s not what we get.

For now, upgrading to Transmission requires buying and changing out a whole-ass drivetrain. Or buying a new bike with Transmission already installed.

There are a whole lot of people out there with perfectly good SRAM 1×12 parts that aren’t compatible with Transmission. And many people with really nice cranks—Race Face NEXT/Era, Cane Creek eeWings, e*Thirteen, Praxis, etc.—with axles designed for narrower-than-55mm chain lines that won’t work optimally with Transmission, and (currently) without compatible chainrings. And that sucks.

I anticipate an aftermarket solution for cranks designed around a narrower chain line: Potentially OneUp’s Switch or Wolf Tooth’s CAMO spider system (or similar) with enough offset and a T-Type compatible ring. But there’s always the possibility of SRAM launching a wave of lawsuits against brands that try to fill what I anticipate will be healthy aftermarket demand with T-Type compatible chainrings.

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The Future

So far, Transmission is only a stand-alone integrated system and not cross-compatible with SRAM’s Eagle AXS. But we can look into the past and use that knowledge to try and imagine the future.

While Eagle AXS drops down to the GX level, there is not yet a GX-level Transmission offering. I expect Transmission to come to the GX level. Maybe, maybe, GX Transmission will be the easy upgrade to a direct-mount derailleur that is compatible with existing Eagle AXS parts. If it is, it will be a massive hit as an upgrade.

I’d count on a close ratio version for DH and park bikes. These would massively benefit from the more-durable derailleur and mounting system.

From there, I think potential next steps from SRAM might include stacking more cogs on the cassette.

As for the future of Eagle AXS: SRAM’s indicating that they plan to continue to produce and support those groups.

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Rear Derailleur

When SRAM introduced the Universal Derailleur Hanger (UDH) in 2019, it didn’t just massively simplify the replaceable rear derailleur hanger landscape. It also prepped thousands of mountain bike frames—and a few gravel frames—for a new rear derailleur mounting system.

T-Type rear derailleurs direct mount (the “hanger” is part of the derailleur) to any UDH compatible frame: Off comes the UDH and on goes the Transmission rear derailleur.

There are significant advantages to the direct mount design. Because the derailleur mounts coaxially, its position relative to the cassette is fixed. The engineers, therefore, know exactly where the derailleur is in relation to the cassette at all times and don’t have to build accommodations into the shifting system for the bike industry’s often loose interpretation of standards and tolerances.

SRAM’s T-Type also eliminates the need for high and low-limit screws and B-tension/B-gap adjustment. That reduces installation to simply bolting the derailleur in place and cutting the chain to the proper length (it’ll vary depending on chainring size and a bike’s chain stay length). In many cases, further adjustment isn’t required, but if it is, the micro-adjustment process for Transmission is the same as with Eagle AXS.

The claimed benefits of Transmission (besides easier setup) are improved shifting under load and durability. Durability, in my opinion, is Transmission’s biggest benefit to riders.

Electronic rear derailleurs cost a fortune. An unfortunate rock strike can destroy derailleurs, along with a rear wheel, and, potentially, a frame. Transmission is so robust it should dramatically cut down on catastrophic failures.

Unlike a standard rear derailleur on a hanger, the Transmission derailleur interfaces with both sides of the rear dropout and is additionally supported by the rear hub and thru axle. Additional security comes from the derailleur’s overload protection—it gives way if it takes a significant hit from the side, then resets to its original position—while a straight-on hit results in the derailleur giving way by rotating backward (riders can reset it to the proper position trail side).

It’s so robust (SRAM representatives illustrated this by standing on the mount) that there’s no need to build any bend/breakaway feature into the mount. But if the rider does smash the derailleur hard enough to cause damage, many of its parts are replaceable. The entire pulley cage spins off with surprising ease. And there’s a replaceable skid plate (XX SL models eliminate the skid plate to save weight), outer parallelogram link, and damper assembly.

A standout detail of the Transmission derailleur is its large pulley cage and lower pulley. The cage yaws as it moves up and down the cassette to keep the chain angled towards the chainring, a detail that reduces noise and improves smoothness, says SRAM. The massive lower pulley isn’t there to reduce drivetrain friction and save watts. Rather it also helps reduce drivetrain noise and vibrations. Though it’s not obvious, the lower pulley utilises a multi-piece design and hides a slipper clutch: If a stick jams into its cutouts, the teeth keep rotating.

Wrapping up the durability story, SRAM claims the T-Type chain is its strongest ever, and T-Type 1x parts are the longest-wearing it has yet made.

The T-Type derailleur uses SRAM’s existing AXS battery packs. SRAM hints that battery life with Transmission might be less than Eagle’s 20-ish hour claimed runtime. SRAM says this is due to Transmission’s increased cage-damper force.

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Chainrings, Chain, and Cassette

While the derailleur certainly is the highlight, there are more parts to the SRAM’s Transmission. There is a new chain, and a new cassette too.

The chain looks like one of SRAM’s road Flattop chains—so named because the top of the chain’s links are flat and without the undulating surface of the links’ bottom—but SRAM insists it’s a unique chain, and the brand’s three 12-speed chains are not cross-compatible.

Although the new Transmission chain (dubbed T-Type) does have the same shape and the larger roller diameter of the 12-speed road flat top chain, SRAM states it has the “Silhouette of the SRAM AXS road chains but has a unique design to achieve its performance.” T-Type chains even get their own special black quick link. There are three levels of chain: the XX SL has cut-out links and hollow pins, XX has hollow pins and solid links, and X0 has solid links and solid pins.

The Transmission T-Type cassette still mounts to an XD driver (phew) and has the familiar 10-52T range. SRAM says the Eagle cassette is not compatible with Transmission, and vice versa. Part of the reason is the T-Type cassettes are 2.5mm further outboard than an Eagle cassette.

SRAM revised cog sizes slightly from the Eagle 10-52T cassettes. Where the Eagle 520 cassette’s low-end progression is 32-36-42-52, the T-Type cassette has a smoother progression: 32-38-44-52. Visible inside the cassette is a red plastic ring. This is a visual aid for Transmission installation and setup only. Also notable are updated construction techniques that, in the XX SL version, result in the lightest 10-52T cassette from SRAM yet—345 grams (the XX and X0 cassettes weigh 380 grams, claims SRAM).

The cassette’s tooth profiles get a rework. Instead of the X-Glide profiles of Eagle, T-Type cassettes have X-Sync teeth, and “retimed shift routes.” SRAM claims the rear derailleur’s, “Firmware references a uniquely timed shift sequence to align with the releasing/receiving cogs,” resulting in continuous chain engagement, and the ability to shift up or down at full power, even going so far as to claim that shifting improves as the rider pedals harder.

As far as what the new chain means for chainrings, it gets confusing. There are new T-Type chainrings for Transmission using the eight-bolt mounting pattern SRAM originally developed for its road drivetrains. The rings come in 32 to 38 tooth and zero or plus-three millimetre offset. XX rings get bolt-on bash plates—if you ride exclusively with one foot forward, you can remove the extra plate. They are optional on the X0 chainrings and eliminated from XX SL rings to save weight.

While the T-Type rings are compatible with Eagle chains, the reverse is not. So, all those existing SRAM MTB cranks and rings that use the three-bolt mounting system are non-compatible with Transmission. And it also means you can’t just buy a T-Type ring from SRAM and mount it on your SRAM mountain cranks with three-bolt mounting.

As SRAM’s 1x road chainrings go, SRAM says that a rider can run a T-Type chain on the brands’ 1x AXS road rings. So, if you have one of the few gravel bikes out there with a UDH (more are on the way), you can run Transmission on that bike too. Like Eagle AXS, the Transmission rear derailleur can be paired with AXS drop bar shifters.

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Cranks and Power Meters

One feature of the cranks doesn’t change: They still use the Dub 28.99mm diameter axle and matching bottom brackets. But as noted above, SRAM adopted the eight-bolt mounting pattern from its road and gravel products. And that’s not the only update to the cranks.

So far, the T-Type transmission only employs a 55mm chain line. This is a point of distinction from Eagle (which comes in as many as six chainl ine options: 49.0mm, 52.0mm, 55.0mm, 56.5mm, 66.5mm, and 76.5mm.) Time will tell if SRAM adds more options. But for now, they state that the 55mm chain line is compatible with Boost 148 and Super Boost 157 rear spacing.

The 55mm chain line brings wider DUB axles (creatively named Dub Wide) and a wider Q-Factor of 174mm. If you’re Q-sensitive, SRAM offers a XX SL crank for a 55mm chain line with a 168mm Q-Factor.

One benefit to the 55mm chain line is it pushes the crank and chainring outboard, which creates more chainring and tire clearance. Basically, a bike can use standard Boost 148 spacing and get some of the best benefits of SuperBoost 157 rear spacing.

XX SL T-Type cranks employ the same hollow-core carbon construction as SRAM’s Eagle XX1 SL cranks. Likewise, the XX T-Type carbon crank’s construction is like the Eagle X01 crank—heavier and more robust than the hollow XX SL crank. X01 T-Type cranks are made of aluminium and feature a striking windowed design.

SRAM offers two power meter options for T-Type. The less expensive and simpler option employs a left arm with the power meter in the axle. This option measures left-side power only and doubles it for total power. Accuracy is +/- three percent.

The other option is a power meter spider. This one is the more expensive and more accurate (+/- 1.5 percent) because it measures left and right leg power independently. This option is particularly noteworthy because it employs a chainring that threads around the circumference of the power meter.

Removing this ring requires a unique-looking tool system from SRAM. But I find an odd tool greatly preferable to the integrated chainring and power meter unit SRAM runs on its high-end road groups. In these parts, when a chainring wears out, the whole unit—rings and power meter—gets replaced in addition to the rings. SRAM’s road team should take a hint from the new mountain product and employ a power meter with a thread-on ring system.

The bolt-on chainring bash guards are not compatible with the power meter spider.

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Pod Controller, AXS Ecosystem, and App

The final new bit of gear debuting with Transmission is the Pod controller. Instead of the Eagle AXS rocker paddle, the Pod has two push buttons stacked vertically.

The pods come in two versions. The Ultimate has replaceable buttons—they snap into place with a tab of double-sided tape offering extra security—and is offered in two shapes: One more concave, the other more convex. The standard pod has flat buttons, and they’re not replaceable. Both pods are powered by a replaceable CR2032 battery that lasts up to 12 months.

The pod controller mounts to a discreet clamp or a Matchmaker clamp which integrates with SRAM’s brake clamps. With either, riders can rotate the pod on its axis, slide it in and out, and rotate it around the bar’s axis to achieve a preferred position. Plus, the pod is ambidextrous and can be mounted on either the right or left side. If you’ve always wanted to shift with your left hand, that’s now possible.

Transmission is part of SRAM’s AXS ecosystem and can be mixed and matched with other AXS parts. The new Pods can be paired with Eagle drivetrains, Reverb AXS dropper posts, and Flight Attendant suspension systems. Likewise, the AXS rocker paddle and AXS drop bar shifters can shift a Transmission derailleur.

Transmission also pairs with SRAM’s AXS app. This allows riders to customise features and push firmware updates.

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Also New—Stealth Brakes

Also dropping today are SRAM’s new Stealth Brakes. This is primarily a hose routing change with a minor name change.

Stealth brakes reorient the master cylinder to place it in line with the handlebar, with the hoses exiting the lever angled toward the bar. These changes make routing look cleaner when paired with a handlebar with internal routing and for bikes with brake hose routing through the headset bearings.

These brakes are still compatible with traditional external routing and internal routing that starts in the down tube. Small clips are included that fit through the stem’s faceplate bolt and hold the hoses close to the bar. The result is a tidy look, with the hoses mostly hidden from the rider’s view.

There are also updated cosmetics and graphics, but functionally the brakes are the same. SRAM also updated the names of the brakes. The Guide 2/G2 name goes away and this brake is now called the Level 4P (four-piston); the existing Level carries forward but is now called Level 2P (two-piston). The other offering is SRAM’s trusty Code.

SRAM also updated the naming of its tiers: The top of the line carries the Ultimate (ULT) designation, while the second tier is named Silver (SLV). The tier names are slightly, and probably unintentionally, confusing because the Stealth Ultimate brakes debut in a silver finish while the Stealth Silver brakes are finished black.