Review: 1,000 Miles on SRAM's New Eagle Transmission

XO Eagle Transmission Details

Cranks

The new aluminum crankset is likely the most eye-catching part of the new groupset, thanks to a cutout in the center of the forged arms, and a polished finish that keeps them looking fresh even after being ridden in gritty mud. The chainring mounts with 8 small bolts (yes, 8 – swapping rings isn't the quickest procedure), and there's an optional bash guard that bolts directly to the chainring in either a single- or double mounted configuration. If you choose to run half of the bashguard, just make sure it's on the bottom of the ring when the cranks are in your preferred pedaling position (left foot forward or right foot forward), since that's when most impacts would occur.

Most of the new drivetrain isn't backward compatible, due to the T-Type chain and cassette design, but the cranks and chainring will work with non-T-Type Eagle chains. Weight: 530 grams without a chainring. Price: $300.


Cassette
The cassette maintains the 10-52 tooth gear spread found on SRAM's Eagle drivetrains, but the spacing between the largest gears has been changed in order to make the jumps less drastic; the final two tooth counts goes from 44 – 52, compared to 42 – 52.

All of the cassettes in the Transmission lineup have the same architecture – the largest three cogs are pinned on, and the nine smaller cogs are machined out of one piece of steel. The 52-tooth cog is aluminum on all the casettes in order to save weight (the XX SL gets 3 aluminum cogs for even more weight savings).

Speaking of weight, the XO cassette checks in at 382 grams, and retails for $400 USD.

Chain
The XO chain has a black finish that SRAM calls 'Dark Polar', and it has a PVD (physical vapor deposition) coating to ward off corrosion and improve its lifespan. Compared to the XX chain, the XO is a little heavier due to the use of solid rather than hollow pins, and it doesn't receive the extra-long lasting 'hard chrome' finish of its more expensive sibling. The XO chain weighs 256 grams and is priced at $100 USD.


Derailleur & Shifter
The heart of the T-Type drivetrain is the new wireless electronic derailleur. It's mounted directly to the frame, occupying the spot where a Universal Derailleur Hanger (UDH) would have been in the past. It's powered by the same batteries used on SRAM's previous AXS derailleurs, although a new shifter design has been added to the mix. The previous shifters are still compatible, bringing the total number of options up to three. The $150 shifter weighs 51 grams and is powered by a CR2032 battery.

When looking at the derailleur from the back of the bike the lower cage appears to be bent. But don't go grabbing a wrench and trying to straighten things out – it's supposed to be that way. SRAM calls it the 'Inline Cage', and the design is supposed to keep the chain pointed towards the front chainring no matter what gear the derailleur is in. The derailleur (with battery) weighs 479 grams and costs $550. At that price it's a very good thing it's designed for durability.




Installation

I've had this Transmission installed on two different bikes over the course of the test period. It started out on a Specialized Stumpjumper Evo, where it was pre-installed by a SRAM technician. After a few months with the drivetrain on the Stumpjumper EVO my tinkering tendencies got the best of me, so I decided to swap it over to a Trek Fuel EX in order to see how the installation process went on my own.

The installation steps are fairly simple, but they are different than a typical derailleur. Even if you're someone who prides themselves on never reading the instructions this is one of those times when at least a cursory glance will be very helpful. SRAM's written instructions make it very straighforward, as does the installation video.


There's no B-tension or limit screws to worry about – instead, the key thing to keep an eye on is that the two marks on the knurled ring and on the full mount of the derailleur (pictured above) are lined up, and that you follow the correct order of operations when it comes to tightening everything down. Chain length is also crucial – SRAM has a list of bikes in their database that can be accessed via the AXS app, or there's a chart that displays the correct chain length depending on chainring size and chainstay length.

Overall, the installation it a quick process, and once the derailleur is in place wheel installation and removal are the same as they are on a 'regular' SRAM derailleur – the cage is extended forward and locked in place to allow wheel removal, and then once the wheel is back on the cage lock is released and the axle is tightened.


Performance

I'm going to date myself here, but I clearly remember when bike shops and magazines would publish charts that explained the ideal way to shift. Those were the days of front derailleurs and triple chainrings, back when there was an art to avoiding cross chaining while still finding the ideal gear. The advent of 1x drivetrains made things a whole lot easier, although in some cases you still needed to take care to avoid pedaling hard and shifting at the same time.

With Transmission, there's really no reason to delay a shift. Cranking up a steep hill and need to shift to an easier gear? Go for it – the chain will pop right up into that gear without any disconcerting noises. I purposely shifted as hamfistedly as possible on a number rides, and in all instances the Transmission worked exactly as claimed.

It's a similar experience to Shimano's Hyperglide+ drivetrains, which debuted in 2019 and also allows for shifting under load. The experience isn't totally identical, though, and in a head-to-head battle of Hyperglide+ vs. Transmission, I'd give the edge to Transmission due to the very quick, and very positive feel that accompanies each shift.

I hadn't realized how accustomed I'd become to the ability to shift whenever, wherever, until I hopped back onto a bike with a 'regular' cable-actuated SRAM X01 rear derailleur. It felt dated somehow, requiring more effort and patience to make shifts compared to the rapid, positive 'chunk' that occurs with the Transmission drivetrain. The shifting performance is also noticeably better than the previous Eagle AXS drivetrains, with a much more solid feel when shifting under load.

The adjusted gear ratios on the cassette are also welcome. Previously, there was a 10-tooth jump from the 42 to 52 tooth ring, which was quite the leap, and left many riders wanting something in between. Now the last four tooth counts are 32 - 38 - 44 - 52, which results in a less drastic change at end of the cassette compared to the 32 - 36 – 42 – 52 spread used previously.

Noise

One of the complaints that occasionally came up with SRAM's AXS Eagle drivetrains was that there was an undue amount of chainslap noise. The clutch wasn't that strong on some of the derailleurs, and the lack of any housing to resist the derailleur body's backwards motion during an impact exacerbated the situation further.

With Transmission that issue has been fixed – the clutch is strong (and hasn't lost any of its holding power over the last six months), and the derailleur body's fixed position helps keep chainslap to a minimum. It's on bigger impacts, ones where the cage is pulled forward and then returns to its starting position that chainslap is most noticeable, but the overall level of noise and chain control is noticeably better than on the previous AXS offerings.




Durability

I try not to smash the back end of my bike into too many rocks and roots, but those impacts do happen, especially on tighter trails where veering off line results in quite literally getting stuck between a rock and a hard place.

In one instance, my front wheel washed out on slippery root that was hidden behind a fern. I hit the ground hard with my right shoulder, and the driveside of the bike took the brunt of the impact. Despite being smashed directly into the ground and covered in dirt the derailleur didn't need any adjustments, and once I'd re-composed myself I was able to keep on riding without doing any trailside repairs.

That was the most dramatic incident, but there were plenty of other moments where it was scraped against rocks, banged against stumps, or subjected to other impacts that could have damaged it... but they didn't.

I've seen comments raising concerns about the possibility of the derailleur breaking a frame due to the lack of a sacrificial hanger, usually followed closely by the conspiracy theory that SRAM got rid of the hanger to sell more expensive derailleurs. In both cases, I'd say those worries are unfounded. The way the derailleur is mounted means the frame is well protected from an impact – it's braced on both sides, and connected to the axle system, which greatly reduces the amount of leverage the derailleur can put on the frame. The force required for the derailleur to affect the frame would be extraordinary, the type of hit that would likely rip a traditional derailleur clean off and shove it into the spokes.

In addition, the derailleur is serviceable – the parallelogram link, skid plate, and cage can all be replaced separately, allowing riders to refresh their derailleur without needing to buy a whole new one.

As for battery life, I'd typically check to see if the light on the derailleur was green or red once a week and charge accordingly. The battery life is said to be a little less than the 20-hour run time of the previous AXS drivetrain, but in practice I didn't notice a dramatic difference.


Weight & Price

As with most new technologies, the initial price of entry tends to be on the higher side before it eventually trickles down to more affordable pricepoints. The XX SL, XX, and XO groups are the three top tiers in SRAM's lineup, but as we've seen in the past a GX version will likely hit the market sooner than later.

At $1,599, the price of a complete XO group certainly isn't cheap – that's around $200 more than Shimano's XTR 12-speed group, and more than double the price of an XT groupset. I realized that comparing the price of an electronic drivetrain to a cable-actuated one is bordering on apples-to-oranges territory, but Shimano doesn't currently have a 12-speed electronic drivetrain for mountain bikes without motors.

When it comes to weight, the XO groupset is within a few grams of a Shimano XT groupset. It ends up being around 40 grams lighter if you subtract the weight of a derailleur hanger and the cable and housing that XT requires. The XO cassette is 88 grams lighter than an XT cassette; the main weight difference ends up being at the derailleur due to the XO's battery and tiny motor.

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Pinkbike's Take

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