SRAM has revealed their new wireless 12-speed mountain bike drivetrain called Transmission. We'll take an in-depth look at price, different models, weight, features, the installation process, and how the SRAM Transmission performs on the track.
If you've ever wondered why SRAM built their own universal derailleur hanger, we've got the answer. While the SRAM UDH interface was arguably one of the best industry-wide accepted standards in recent years, it's now clear that it was just a Trojan horse for the real plan behind its design. SRAM's new derailleur features a direct-mount derailleur, a new crankset and a cassette with SRAM's T-chain.
SRAM Transfer Highlights
- Direct mount derailleur interface
- Completely redesigned cassette
- T-chain interface
- Redesigned modular shift bay
- New crankset with optional crash plate
- Individually replaceable parts
- E-Bike Compatible Crankset Options
- New invisible brake lever
- Recommended retail price as tested
- XX Model T Eagle Transmission Dynamometer AXS Kit - $2299.00
- XX rear derailleur - $650
- AXS POD Ultimate 2 Button - $200
- XX crankset with Quarq power meter - $950
- Cassette Tape XS-1297 T-Type Eagle - $550
- XX T Hollow Pin Chain - $125
Mountain bikes with a UDH interface are required to run a transmission, so if your frame and derailleur hanger are not UDH ready, the transmission will not work with your bike. With the exception of pod controllers and derailleur batteries, Transmission is not backwards compatible with existing SRAM Eagle drivetrains, AXS or cable drive systems.
The gearbox runs on a T-chain interface that has a flat top similar to their road group. The drivetrain requires a T-chain, as previous non-T Eagle chains would not work with the gearbox. However, T-chains can be used with previous Eagle components.
At the time of writing, the new crank and chainring interface uses 8 bolts, compared to 3 bolts on the previous Eagle. This means that until SRAM or an aftermarket brand make a compatible chainring, you have to run a SRAM crank with a gearbox.
The AXS Pod Controller works with previous Eagle AXS derailleurs or dropper posts. Previous Eagle AXS controllers will also work with Transmission.
Do not do this. SRAM non-T Eagle chain on the transmission drivetrain. The chain doesn't hold onto the links securely.
SRAM transfer price
SRAM gearboxes come in 3 groupsets: X0, XX and XX SL. We were sent XX group to test. Components at the 3-group level differ in structure, material, or function, which affects weight, price, and performance.
All prices are in USD
Transmission derailleur only, battery not included
- Transmission X0, $550
- Gearbox XX, $650
- Transmission XX SL, $650
Transmission box price
- X0 XG-1295 Model T - $400
- XX XS-1297 Model T - $550
- XX SL XS-1299 Model T - $600
- AXS Pod - $150
- AXS Pod Ultimate - $200
SRAM T-Chain Prices
- X0 - $100
- XX - $125
- XX SL - $150
Transmission Dub Crankset Prices (with chainrings)
- X0 is Q174 alloy, includes double guards and 32t chainring - $300
- XX - Carbon, Q174 w/dual guards & 32t chainring - $500
- XX SL - Carbon, Q168 w/o guard & 34t chainring - $550
Chainring or spindle dynamometer options available.
SRAM Transmission Kit Prices
Transmission kit including derailleur battery and charger
- X0 $1,599
- The XX, like the one we tested, starts at $2,049
- XX SL groups start at $2,199
We weighed the Transmission XX parts we received, as well as the previous Eagle AXS X01 and Cable Drive X01 parts, to compare approximate new and old weights.
- Gearbox XX with battery - 465 grams on our scale
- SRAM's claimed weight for gearboxes XX SL, XX and X0 - 440g, 465, 475g
- Since Transmission does not require a transmission hanger, we added UDH hanger weights to previous models
- Original AXS Eagle X01 with battery - 390g (without UDH), 417g (with UDH)
- Cable Eagle X01 - 287 grams (without UDH), 314 grams (with UDH)
- SRAM Transmission XX 10-52t XS 1297 T-Type - Ours weighed 379g
- SRAM's claimed weight for gearboxes XX SL, XX and X0 - 345, 380g and 380g
- Eagle X01 10-52t XG 1295 - 375g
- Transmission AXS Pod with Discrete Infinity Clamp - 47g
- Original AXS with discrete clamp - 86g
- Eagle X01 with cable, 124g, without clips (discrete clips + 11g) or housing, should be factored into system weight
We put them in boxes to keep things clean. The XX case weighs 42 grams.
- SRAM XX Eagle T, 126 links - 352 grams on our scale. 247g, SRAM claims (possibly 108 links? SRAM weighs 33g more than our scale, without case)
- SRAM X01 Eagle, 126 links - Our scale weighs 296g
SRAM Eagle Transmission XX crankset weight, 175mm length, with dual impact guards
- 553 grams for our weight
SRAM currently does not have crankset weights available, nor do we have any previous Eagle cranksets to weigh.
SRAM wanted a transmission with foolproof setup, easy maintenance and unmatched durability, all while being able to shift under heavy loads. The derailleur fits around the bike's rear axle, with contact points on either side of the frame. This ensures perfect alignment between the derailleur and cassette on any bike. It is claimed to have a breakaway force of 600 lbs. Vital Tech editor Jonny Simonetti, who is 6-foot-4 and 220 pounds, walked on the derailleur countless times to emphasize its durability. Like the AXS before it, there's a breakaway clutch so the derailleur can move inward on impact.
The new derailleur cage design takes some precautions in the form of a longer lower guard to keep curb objects from being sucked into the lower sheave. If an object gets into the lower pulley, the "magic pulley" on the XX and XX SL models allows for freedom of movement by using a metal inner wheel and a plastic outer ring that slides along an inner track. While continuing to take precautions, SRAM researched which parts of the derailleur are in contact with the road most often and reinforced them with bumpers to prevent damage to critical components. Plus, these parts are all individually replaceable, so consumers don't have to pay for new derailleurs in the event of a breakdown. Best of all, it allows X0 derailleurs to be upgraded to XX or XX SL cages to add Magic Pulley or reduce weight. The cage can be disassembled without the use of tools. The cage is attached with coarse threads to lock into place, and the clutch tension seems to be able to handle more force than previous generation AXS derailleurs.
The all-new shifter features intuitive buttons that will be familiar to those who have used the previous-generation AXS system. The difference is a more defined click and less lean. The previous generation controller is forward compatible with the transmission, and if the user prefers the old style, the new Pod will run the previous generation AXS drivetrain. Pod Ultimate on XX and XX SL offers two sets of concave or convex buttons. The Pod is universally programmable, which means riders can customize the buttons for different functions. On top of these buttons, the shift pod itself is symmetrical, meaning the left and right units are identical, for a total of four buttons available. They can be used with RockShox Reverb AXS and Flight attendant, but also allow for eTap-style road shifting setups (i.e. downshifting on the left, upshifting on the right) or any combination the user prefers.
T-Type Eagle Cassette Tape
The new 12-speed T-cassette offers higher shifting performance than previous generations of cassettes thanks to tighter tolerances between the frame and cassette and the fit of narrow, wide X-synchro gears throughout. The gear ratios are smoother too, with the largest 52t cog now down to 44t and 38t cogs. Inside the 5th highest gear of the cassette there is a red plastic inner ring that sets the B tension and simplifies the setting process. The XX SL cassette uses aluminum on the 52t, 44t and 38t rings, the XX uses aluminum on the 52t ring, and the X0 is nickel-plated steel for e-MTB use.
The new range of cranks includes XX, XX SL and X0 models. The 8-bolt chainring interface integration is the same as in SRAM's road bike range. This means that previous SRAM chainrings cannot be used with cranks. The XX SL comes with a new power meter integration that is said to improve data accuracy. The X0 cranks have been completely redesigned with some very striking aluminum design elements and weigh less than Shimano XTR cranksets. The XX and XX SL feature carbon fiber arms. All chainrings are compatible with two metal impact guards mounted 180° apart.
In addition to the gearbox, there are all-new invisible brake lever bodies, which came in the form of Code Ultimate on our test bike. Performance-wise, the brakes themselves are unchanged, with the same chromed calipers as the current generation. They used a carbon stem blade that wasn't previously on the Code model. The purpose of the Stealth lever is purely aesthetics and part of SRAM's quest to create what they believe is the cleanest cockpit by eliminating cables and hoses from sight, while mirroring the design cues of the transmission components.
Starting with the XD driver, SRAM defines the position of the cartridge edges and end caps. Strapping the end cap directly to the derailleur creates the tightest possible tolerance between the cassette and the derailleur, eliminating the need for upper and lower limit adjustments. During setup, the B limit key on the hanger sets the B tension position when the derailleur is twisted onto the frame. Cage lock button can now be flipped to A or B position. The derailleur will use the A setting, while the B setting is for bikes with higher levels of chain growth. The updated AXS app now has chainstay length data for nearly every UDH-compatible bike on the market to determine proper chain length. Just enter bike info and chainring size. The B tension lock position and cassette setting gear will be determined by the app. Chain length can also be determined by measuring the chainstay length and pairing it with the chainring size on the chain length chart provided by SRAM. Installation of the new derailleur is very simple and only takes a few minutes after hanging the parts, mating and securing the parts. SRAM describes the setup process as three steps: cutting the chain to length, hanging the parts on the bike, and screwing everything down.
The first few shifts of the new drivetrain had us wondering if a gear had been shifted, and that's somewhat to be expected for a close-ratio 12-speed drivetrain. The addition of a more closely spaced second gear on the new cassette is very welcome and makes for a very useful climbing gear. Where we really started to scratch our heads was over load, and on the throttle, shift changes remained seamless despite our best efforts to create problems. When SRAM's Chris Mandell put our test bike on its side, stood on the derailleur, and demonstrated how the new drivetrain continued to shift seamlessly after doing so, we found ourselves with our hands above our heads, laughing to death . Since then, we've trampled on it countless times to impress others. In short, the new installation interface is legitimate.
on the way
Our introduction to Transmission began in January with us in Bellingham, WA, where we spent three days spinning some steep climbs in the saddle and rushing down even steeper climbs between Lookout Mountain and Galbraith downhill. Conditions were wet and messy. It was a great introduction to the gearbox, and it was able to let us ride it all day and push the bike to the highest limits we were comfortable with while getting familiar with the new interface. Making a more direct comparison to what we ride every day from Bellingham back to Phoenix, noticed an immediate improvement in shifting under load on the technical climbs of the South Mountain. From Phoenix, we visited Northern California with steeper descents and sustained climbs. We then headed to Southern California for a higher speed descent combined with a sustained/technical climb. Back home, we raced an underground enduro to see how it fared in the less expected race scenario.
DH/tech performance/fun factor
When descending, the most obvious difference between the transmission and the previous generation SRAM AXS drivetrain is how quiet it is. A common complaint from many AXS users is the noticeably louder chain slam from the derailleur compared to cable drive models. For the transmission, the clutch spring tension is said to be similar to the previous model, but the chain retention has been improved for a quieter ride. We were pleased with how quiet the test bike was and felt confident pushing the bike as hard as we could without worrying about losing the chain.
Shifting under load is where the transmission shines, most noticeably when changing gears on hill climbs. Since the system only shifts at precise flywheel ramp positions, individual shifts are seamless, with zero break-in cadence, or the need to plan shifts. The real thing to watch out for is the quick transition from descent to climb and vice versa. Compared to previous-generation AXS components, where each press of the remote caused the derailleur to shift instantly, the new transmission shift pattern took some getting used to and required us to keep track of the number of clicks during quick shifts. Since the system only allows the derailleur to shift on precise shift ramps, the system will queue up shifts while waiting for said ramp, which can cause delays in some cases. In our experience, when trying to get through the flywheel as fast as possible, this often results in more shifts in line than expected, and once all shifts are done, we end up in a higher or lower gear than expected. While it's a nuance, it's worth noting that the system's shifts were smooth during our testing, especially when a gear or two was required on hill climbs. Programming multiple gears does also increase shift speeds slightly.
The entire transmission system is undeniably unique, and nearly every part of our XX class packs cool features. The derailleur mount interface is the biggest talking point, and being able to stand on it without any impact is pretty shocking. The built-in protection features that keep things running smoothly are appreciated. From a rider’s perspective, the first thing we noticed was the new modular shifter, which has a different feel to the previous generation paddles and the ability to swap buttons. The jagged lines on each mounting interface of the shifting pods are very useful and will make it easier to set up the pods between different bikes.
room for improvement
With so much improvement over the past six years, it's hard to imagine any room for improvement, and at Transmission's level, that's really nitpicking. As technophiles, we've certainly discovered some things we can change. First and foremost, the multi-shift option is one thing we've gotten used to. This has to do with the systematic approach and complexity of the system, which allows shifting only at precise shift ramp locations on the flywheel. While this is undoubtedly the main reason the transition is so perfect, it makes timing it rather difficult when so many of us are used to transitions happening in an instant. It's worth noting that pedaling harder does help shift gears faster.
price? Well, that's a moot point for a product of this range. We can only hope that the GX version comes out soon.
We see long-term durability as the transmission's strong suit and don't expect any major issues for many years to come. In addition to the unrivaled strength of the rear derailleur, the crash guard mounted on the replaceable chainring should keep the chainring from breaking for an extended period of time and has two mounts that can be adjusted depending on which foot the user is with Replace the front derailleur together or leave one alone. The only potential wear part that needs to be replaced after a season or two of use is probably the shift button. We opted for the concave buttons and found that the grip pattern softened slightly over time, as with any pair of grips. We see this pattern fade over time. That being said, even if the graphics are completely worn out, the shifter will still be 100% functional, and these items are fairly inexpensive to replace.
What's the bottom line?
Throughout the test period, the system maintained incredibly smooth shifts in every situation we handled. If we were to choose a drivetrain for our next bike, it would undoubtedly be the gearbox. Actually, affordability might be another thing, but from a longevity standpoint, it might even end up saving you money in the long run. With features like Magic Pulley, built-in skid plates, and tool-less cage removal, it's great that SRAM is focusing not only on its racers, but on the average consumer as well. Being able to replace individual derailleur parts as needed constitutes a huge advantage, and with the mounting interface providing unrivaled durability, you can see the derailleur starting to outlast the frame. Our complaints about correct shift times require longer settling times to develop better muscle memory, but we can only describe shift performance as class-leading for how smooth the shifts were in every situation we tested.
For more information, clickSRAM.commore details.
Jonny started mountain biking in 2003 and on a trip to Northstar he showed him that he could do a lot more riding on 26" wheels than on a BMX bike. He started racing downhill in 2004 and raced for 12 years before deciding that having fun on the bike was more important than race results. After working as a mechanic in the industry for a few years and gaining a better understanding of bikes inside and out, he was able to combine his riding prowess with bike analysis and break down why a bike worked so well. He spends most of his time between off-road riding and skate park training, with the occasional downhill bike.
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