Wil reviews the SRAM Eagle 90 Transmission

Today SRAM launches not one but two brand new mechanical Transmissions. Called Eagle 70 and Eagle 90, these drivetrains follow in the footsteps of the first AXS electronic Transmissions that arrived in 2023.

Initially offered at the XX SL, XX and X0 spec level, SRAM’s innovative Transmission made waves by removing the traditional hanger in favour of mounting the derailleur directly to the frame. As well as being a lot stronger and easier to setup, it also allows for impressive shift performance under load, an aspect that really shines through on an e-MTB.

SRAM went on to launch the cheaper GX and S1000 AXS Transmissions that brought down the price of entry, though we were still curious as to whether it would ever produce a mechanical version. As it turns out, the engineering team actually started prototyping a cable-operated T-Type derailleur no fewer than eight years ago. The decision was made to bring the electric AXS groupsets to market first (a smart move no doubt), while SRAM quietly worked away behind the scenes to bring its Transmission tech into a fully production-ready mechanical groupset.

With the arrival of the new Eagle 70 and Eagle 90 drivetrains, SRAM now has seven different Transmission options to choose from. It sees the US brand turning up the heat against its Japanese rival, which has largely dominated the mid-tier drivetrain market thanks to its SLX and XT groupsets. If Shimano wasn’t already worried before, then it should be now!

Watch our video review of the SRAM Eagle 90 Transmission:

Shift performance under load is excellent, and the cable-operated shifter gives it a nice tactile feel that will be appreciated by folks who are less enamoured by electronic buttons, smartphone apps and rechargeable batteries.

An overview of SRAM’s new Eagle 70 & 90 Transmissions

The SRAM Eagle 90 Transmission and Eagle 70 Transmission are both 12-speed drivetrains that feature cable-operated shifters and derailleurs.

Eagle 90 is essentially the mechanical version of the GX AXS Transmission. In fact, the cassette, chain and crank arms are the same. Aside from a new steel chainring, the key difference is the mechanical derailleur and shifter. According to SRAM, Eagle 90 represents the pinnacle of mechanical shifting and it features the most rebuildable derailleur ever.

Eagle 70 sits one level down. It effectively replaces NX Eagle, and is the mechanical equivalent of the S1000 Transmission. Indeed it shares the same crankset, chain and XS-1270 cassette, the latter of which mounts using the older HG freehub standard. The cable-actuated derailleur is similar to the Eagle 90 version, but the use of cheaper materials and the Drag Spring damper helps to bring the price down.

It’s the SRAM Eagle 90 Transmission that I’ve been testing alongside the new Motive Ultimate brakes, and here I’ll be taking you through all of the juicy details that make up this groupset, followed by my impressions from the past month of riding.

SRAM Eagle 90 Transmission price & weight

• Weight: 2,112g (including gear cable, no BB)
• Price: $1,150 AUD

The SRAM Eagle 90 Transmission components will be available to purchase on their own or as a complete groupset. With the exception of the BB, you’re looking at $1,150 AUD for the whole kit and caboodle. If you own an e-MTB and don’t need the crank arms, the price drops down to $1,015 AUD.

To put that figure into perspective, it is significantly cheaper than the GX AXS Transmission ($1,889 AUD). However, it is more expensive than a Shimano XT drivetrain, which you can typically purchase for less than $800 AUD.

Speaking of XT, it’s worth acknowledging that the Eagle 90 Transmission is heavier (2,112g vs 1,866g). Much of that weight difference can be attributed to the XT’s lighter crankset and derailleur.

Not everyone is going to be fussed by the extra 250g, especially if there are improvements to shift performance and durability. So, what does the Eagle 90 Transmission bring to the party?

SRAM Eagle 90 Transmission Derailleur

• Weight: 390g
• Price: $325 AUD

Like its electronic siblings, the SRAM Eagle 90 derailleur utilises a Full Mount design that sees it attaching directly to your frame with no need for a separate hanger. It’s only compatible with UDH dropouts, which means owners of older mountain bikes are sadly out of luck.

SRAM claims that Eagle 90 is its strongest and most rebuildable mechanical derailleur to date. In addition to the replaceable skid plates you’ll be able to purchase spare P-Knuckle and B-Knuckle assemblies as well as a bushing replacement kit. Jockey wheels and the derailleur’s inner cage will be available separately, or as a complete package with the entire cage and damper.

On the note of the cage, it is identical to a GX AXS Transmission derailleur with its steel outer plate and alloy inner plate. You can unthread the whole assembly and damper from the body of the derailleur without any tools required, and the modular interface means you could swap it out for a higher end version from an X0 or XX SL derailleur.

Confirmed weight for our Eagle 90 derailleur is 390g. It’s a hefty chunk of metal, but it’s still 100g lighter than the GX AXS version. For some context, here’s the confirmed weights for some SRAM and Shimano derailleurs;

• Shimano XTR Derailleur + UDH Hanger – 270g
• Shimano XT Derailleur + UDH Hanger – 306g
• SRAM GX Eagle Derailleur & UDH Hanger – 328g
• SRAM Eagle 90 Transmission Derailleur – 390g
• SRAM XX SL Transmission Derailleur – 445g
• SRAM GX AXS Transmission Derailleur – 489g

SRAM Eagle 90 Transmission Shifter

• Weight: 132g (including inner cable)
• Price: $85 AUD

Up at the cockpit is a brand new Eagle 90 trigger shifter. It features a specific cable-pull ratio to match up with the T-Type derailleur and cassette spacing, which means there’s no cross-compatibility with previous Eagle mechanical drivetrains.

The shifter is offered in a double-click version for normal mountain bikes, as well as a single-click shifter that’s purpose-built for e-MTBs. As with previous mechanical SRAM shifters you’ll find a small paddle for up-shifting, and a larger lever for down-shifting. In the case of the Eagle 90 shifter the upper paddle is plastic, while the lower paddle is made from alloy and incorporates some machined grooves for texture.

The MMX system allows the shifter to mount to your handlebar using a standalone clamp, or directly to a SRAM brake lever using the relevant adapter. Once fitted, you’ll notice the straight cable path that runs parallel to the bar to allow for a neat match with SRAM’s latest Stealth brakes.

SRAM Eagle 90 Transmission Crankset

• Lengths: 155, 160, 165, 170 & 175mm
• Chainring: 30, 32 & 34T
• Weight: 824g (including supplied 32T chainring & bash plates)
• Price: $265 AUD

The SRAM Eagle 90 crankset utilises the same alloy crank arms as GX AXS, albeit with a black finish and a steel bolt. It’s built specifically around the modern 55mm chainline standard and features a DUB Wide spindle. The arms are available in lengths from 155-175mm, and there’s even an e-MTB specific version to fit Bosch and Brose/Specialized motors.

Unlike the GX AXS crankset, the Eagle 90 version is equipped with a new steel one-piece chainring. It’s twice as heavy as an alloy chainring, but it offers approximately three times the wear life and it’s also quieter in use. Because the Eagle 90 crankset incorporates the latest 8-bolt interface, it’s easy to change to a lighter alloy chainring or even a powermeter if you feel so inclined.

SRAM will offer 30, 32 and 34T chainring sizes, and the two-piece bash plates will come fitted as standard.

SRAM GX Eagle XS-1275 Transmission Cassette

• Weight: 443g
• Price: $429 AUD

The SRAM Eagle 90 Transmission makes use of the existing XS-1275 cassette from the GX AXS drivetrain. It’s designed to fit onto a XD freehub body and is optimised for 55mm chainline spacing.

Featuring a huge 520% gear range with a 10-52T spread, the cassette utilises a pinned construction for the eight largest sprockets and a single mini-cluster for the smallest four. The largest 52T sprocket is made from alloy while the rest are steel with nickel plating for improved durability.

Of note is the narrow-wide tooth profile, which SRAM calls X-Sync. This is designed to match up with the chain to provide better retention along with specific shift gates both up and down the cassette. It’s a big part of the Transmission story, and it results in impressively reliable shifting even under hard pedalling loads.

SRAM GX Eagle Transmission Flattop Chain

• Weight: 263g
• Price: $85 AUD

As with the cassette, the GX Flattop chain is brought over to the Eagle 90 Transmission. It incorporates a Flattop design that is specific to Transmission, and it’s treated with a PVD coating to improve resistance against wear and corrosion.

Unlike higher-end SRAM chains, the GX version sticks with slightly heavier solid pins. However, it uses the same Powerlock master link that allows you to easily connect the chain during installation.

Installation

Setting up the SRAM Eagle 90 Transmission is nearly identical to the electronic version. There’s obviously no hanger to align, and you don’t have to worry about the usual limit screws and B-tension adjustment found on other cable-actuated derailleurs. Not only does this speed up installation, it removes some of the variables that can lead to poor shift performance or even failure.

The only adjustment you have to consider is the A/B setup key, which for most full suspension mountain bikes will need to be set to the B position. You can confirm this via SRAM’s online guide, which is also used to determine the exact chain length by taking into account your bike’s chainstay length and chainring size.

From here it’s a case of bolting on all the components as usual. However, there are two key differences when setting up the Eagle 90 derailleur compared to the AXS equivalent.

The obvious one is the addition of a gear cable, which you’ll attach at the end of the process. The other point of difference is accessing the setup cog when tensioning the chain. You’ll need to open the derailleur up and insert a 4 or 5mm hex key into the dedicated receiver underneath, which locks it out in the necessary position over the setup cog.

Otherwise you tension the chain and tighten the derailleur’s main bolt using the same method. Aside from dialling in the cable tension, that’s kind of it. Simple eh?

How does the SRAM Eagle 90 Transmission perform on the trail?

I’ve had no real surprises thrown at me from the SRAM Eagle 90 Transmission throughout testing so far. It performs its job as intended, with mostly smooth shift performance that is particularly reliable under load. It’s a notable improvement over previous Eagle mechanical drivetrains, with less noise and more positive engagement as the chain locks into each gear.

Chain retention and shift speed is similar to the GX AXS Transmission, which is to be expected given they share the same derailleur cage assembly, cassette and chain. As such, I haven’t found shifting to be quite as crisp as the pricier X0 and XX Transmissions, which feature a more premium construction that leads to better precision and less noise. I’d also suggest that a Shimano XT drivetrain delivers slightly quicker performance, at least when new anyway.

One thing I noticed early on with the Eagle 90 Transmission is that it can be a little lazy going into the smaller cogs if you’re soft-pedalling. Really this drivetrain wants you to shift under load, which took me some time to recalibrate compared to an AXS equivalent. I believe this is due to the tactile connection between your thumb and the movement of the derailleur, which meant I couldn’t help but ease off the torque when changing gears thanks to three decades worth of muscle memory. Within a few rides however, I became comfortable pushing the Eagle 90 derailleur forcefully through each shift. Furthermore, as all the intermeshing components have bedded in during the first 200km of riding, it’s only gotten smoother.

Lever ergonomics are excellent with a positive feel to each paddle. The action is fairly light, requiring less thumb force compared to a Shimano XT or XTR trigger shifter. It’s not quite as snappy as the mechanical XX1 shifter on my Specialized Chisel Hardtail, and the main lever doesn’t offer the same degree of adjustability. There’s also a smidge of freeplay before each click, but it wasn’t something I really thought about once riding. That being said, I do think there’s room for SRAM to introduce a higher-end version of this shifter and derailleur, especially for those like me who appreciate a nice mechanical drivetrain.

Some folks may be bothered that you can only downshift up to two gears at a time, though I’m absolutely fine with this if it means the chain remains properly engaged with the cassette and minimises the chance of damage. Indeed Transmission places a big focus on reliability and durability, and we’ll note that we’re yet to break a chain on any of the drivetrains we’ve tested, electronic or mechanical.

Upgrade options

It’s worth noting that there is a heap of inter-compatibility between all of SRAM’s T-Type Transmissions, which means you can mix and match across all seven groupsets depending on your requirements.

For example, if your bike came fitted with an Eagle 90 Transmission and you were keen to go wireless, you’d only need to purchase an electronic derailleur and controller. Conversely, owners of an existing AXS Transmission who have a desire to get away from batteries could do the opposite.

There are more nuanced possibilities too. If you wanted crisper shift performance, it’d be entirely possible to build your Eagle 90 groupset using a X0 cassette and chain. You could also drop a decent chunk of weight by upgrading to a carbon XX crankset, and there’d be further grams to save if you changed the derailleur cage assembly for the XX SL version. That would bring the Eagle 90 derailleur down to 346g, which is pretty darn light.

Speaking of weight, the new direct-mount chainring is certainly not the lightest option. However, it does run noticeably quieter than an alloy equivalent and in theory it’ll offer about three times the lifespan. Given it’s usually the chainring that needs replacing first on a Transmission drivetrain, that should end up costing you less money in the long run.

Any downsides so far?

Aside from making some adjustments to the cable tension and removing a stiff chain link, I’m yet to encounter any significant issues with the SRAM Eagle 90 Transmission.

Of course any cable-operated drivetrain will require periodic maintenance, which differs to an electronic derailleur that should maintain its shift performance over a long period of time. On the flip side, there’s no battery to remember to recharge, so each system has its pros and cons.

As mentioned earlier, shifting into the smaller cogs can sometimes lag if you’re not being assertive with the Eagle 90 Transmission. The worse you treat it the better it performs, which does take some getting used to. Given its preference for high-torque gear changes, I expect it’ll work very well on a bike with a motor.

While it hasn’t caused me any dramas, I have noticed the Eagle 90 derailleur sticks out quite a bit. When positioned in the 10T cog the outer knuckle sits 36mm away from the dropout, which is considerably wider than an AXS Transmission or Shimano XTR derailleur. Combined with the low-hanging derailleur cage, it’s potentially more vulnerable to strikes from wayward rocks and tree roots. Perhaps that explains why SRAM is offering so many spare parts for the Eagle 90 derailleur?

Skeptical conjecture aside, only time will tell as to how durable this new mechanical Transmission is once it’s out in the mass market. I’ve had great experience so far, though I’m curious to see how it fares in the longer term, especially compared to a cheaper and lighter Shimano XT drivetrain. There are a number of benefits to SRAM’s hanger-free approach, and and the way it’s optimised for modern 55mm chainlines means it never feels strained in the lower gears. The fact that the derailleur is fully rebuildable also gives it a significant advantage over its Japanese rival, and is something to be commended. Even if Eagle 90 is a bit heavier and more expensive to buy in the first place, if it’s more durable and retains its shift performance for longer that could see it edging ahead for many riders.

Flow’s Verdict

The SRAM Eagle 90 Transmission is a welcome addition to the array of modern mountain bike drivetrains. It adopts many of the features that we love about the electronic versions, including the hanger-less design and simple setup process, albeit in a much cheaper package.

Shift performance under load is excellent, and the cable-operated shifter gives it a nice tactile feel that will be appreciated by folks who are less enamoured by electronic buttons, smartphone apps and rechargeable batteries. The fact that you can fully rebuild the derailleur will also appeal to hard-hitting riders who might worry about having an expensive AXS mech hanging off the back of their bike.

While cheaper than its electronic counterpart, the Eagle 90 Transmission is still more expensive than a Shimano XT drivetrain. There are important advantages to the Full Mount derailleur however, which eliminates some of the key variables that can affect shift quality and durability. Our experience so far has been positive, and we look forward to spending more time on the SRAM Eagle 90 Transmission to see just how tough it is in the long run.

The fact that you can fully rebuild the derailleur will also appeal to hard-hitting riders who might worry about having an expensive AXS mech hanging off the back of their bike.

ABOUT THE REVIEWER - Wil Barrett

Hometown

Bendigo, Victoria

Height

175cm

Weight65kg