SRAM revolutionised MTB drivetrains over ten years ago with the launch of the single-ring XX1. Now, its new XX and X0 Eagle AXS transmissions promise equally significant gains in strength, durability and set-up simplicity. That could be enough to put them firmly on the list of best MTB drivetrains and groupsets.

*Now updated after 16-months of riding.

Need to know

• Complete new transmission options at XX and X0 levels for XC, trail and e-bikes
• New ‘Full Mount’ derailleur exploits UDH hanger interface
• Mech is stronger and fully rebuildable
• Simple set-up – no adjustment screws
• New shifting ramps and evenly spread gear ratios
• Single shifter pod can be used both sides
• Designated ‘T-Type’, the new Eagle parts are not backwards compatible with old Eagle
• Runs a 55mm chainline
• For a detailed rundown of all three drivetrains, read all you need to know about the new SRAM Eagle AXS ecosystem

In all the years of mountain bike development – from triple chainsets and five speed blocks all the way through to single-rings, wide-range cassettes and wireless shifters, the mech hanger remains the weakest link in the whole system. Designed to be a sacrificial part in the event of a crash, it is also the root cause of most poor shifting problems. True, there are other options on the market – gearboxes, hub gears (such as the Classified system) and left-field alternatives such as the Lal Bikes Supre Drive – but the efficiency, weight and simplicity of a ‘traditional’ drivetrain is still hard to beat.

SRAM’s new Eagle transmission aims to transform this Achilles’s heel into something more like Zeus’s bicep, with a robust mount that uses the rear axle and UDH frame interface to give it unprecedented strength. And with the axle acting as a consistent reference point between mech and cassette, SRAM has been able to do away with all of the adjustment screws, making installation a doddle.

Furthermore, every element of the complete drivetrain system has gone through a comprehensive redesign. It’s clear why SRAM has taken this holistic approach when you put all the pieces of the puzzle together, even if that means it’s not backwards compatible, and upgrading to the new transmission is a significant investment.

XX rear derailleur £695 w/out battery

Weight: 441g w/out battery (battery 25g)

The new ‘Full Mount’ derailleur is quite literally the linchpin of the whole transmission, but it was SRAM’s Universal Derailleur Hanger (UDH), and its widespread adoption by frame manufacturers, that paved the way for its existence. The idea of a stronger derailleur is not a new one – Shimano tried to launch its own a decade ago, while Specialized developed a reinforcement bar even further back than that. So, for SRAM’s concept of a stronger, simpler, more reliable drivetrain to succeed where others have failed, it had to convince bike brands in sufficient numbers to redesign their frames. This campaign started in 2018 and now, five years later, there are thousands of mountain bikes with UDH hangers on the market, all of which are compatible with the new Eagle transmission.

You must remove the UDH to mount the new derailleur. Then press a top hat bushing into the frame. The mech then embraces the frame like a clevis suspension pivot, and the rear axle slides through the middle, held in place by a threaded end cap that keeps the derailleur at the correct angle. SRAM has christened the new design ‘Full Mount’.

Comparing the old and new mech side by side, in the same gear, the new XX derailleur sits over 5mm further inboard at its widest point. So while SRAM’s new full mount doesn’t completely solve the derailleur’s fundamental vulnerability – it’s still the lowest point of the bike after the wheels, and clearance remains limited, particularly on mullet bikes –  it is significantly less vulnerable to impacts. And being significantly more robust, it shrugs off certain impacts when you do hit something.

Visually, the new XX mech is much more angular, with crisp chamfers, tight radii, and sharp edges. Shiny polished surfaces are used for high wear areas, so they should resist scuffing and stay looking fresh for longer. In addition, ‘Skid Plates’ are bolted to the most vulnerable edges of the parallelogram, and they can be easily replaced in the event of an impact.

Gone are the upper and lower limit screws and the B-gap screw. With the mech now tethered to the axle, and precisely orientated on the frame, the relative position of the derailleur and the cassette is known and consistent. That means there’s no need to customise the mech to every individual bike. Just bolt it on and go.

Even setting the B-gap is simpler. Now it can be done in the workstand with a single tool, rather than with someone sitting on the bike and a helper fiddling around on the floor. Just run the chain over the 21t sprocket on the cassette (marked with a red ring), put the mech in a second lock position, pull back the derailleur until there’s no slack, and torque up the mech bolt to 35Nm (the original 25Nm recommended at launch has been increased). You may have to flip the cage lock insert between position A or B depending on your bike and how much chain growth it has, but an online resource gives the settings for your bike. Most full-suspension bikes are A, most hardtails are B.

The new Eagle mech is stronger and easier to set-up then, but it’s also designed to be quickly and easily repaired. The cage unscrews from the parallelogram by hand. You can remove the pulley wheels with a Torx key, and most of the parallelogram can be taken apart with a couple of Hex keys. All of the parts will be available aftermarket, so you can make repairs or refurbish your drivetrain ready for resale.

Further protection is provided by the Overload Clutch, that pulls the mech inward after an impact, such as a rock strike, and a Magic Wheel lower pulley, that lets the outer teeth continue to rotate if a stick jams in the spider. Also available is an XX SL mech with a black finish and carbon parts that save 20g for £695, and a X0 level option for £590.

For reference a non-T-Type XX1 AXS rear derailleur costs £742 and weighs 352g w/out battery, but obviously that doesn’t include the weight of a UDH hanger (26g).

XG-1297 Cassette £590

Weight: 380g Sprockets: 10, 12, 14, 16, 18, 21, 24, 28, 32, 38, 42, 52t Freehub fitting: XD

Although it’s hard to see, the new XG-1297 cassette, and its siblings, the XG-1299 and XG-1295, are significantly different to older Eagle models. The headline changes are closer ratios for the lowest gears – now 38, 44, 52 instead of 36, 42, 52 – and the introduction of X-Sync profiling for 11 out of 12 sprockets. This narrow-wide sequencing forces the chain to wrap the sprockets in a specific way. Cleverly, this means that SRAM knows exactly where every inner and outer link will be at any given time, so it can precisely position the shifting ramps to eliminate delayed or rejected shifts. The idea is that you no longer have to think about your shift position or drivetrain load – just punch the controller and go, even on a full power e-bike.

Teeth are now very slightly wider than previous cassettes (which is why the new drivetrain is not compatible with older designs), because the new mech interface has freed up just under 2mm from the dropout area. Extra width means more material, and more material should mean greater durability.

For reference the non-T-Type XG-1299 cassette costs £453 and weighs 357g.

XX Chain £135

Weight: 261g

There’s a new flat-top chain to work with the thicker teeth of the latest cassette. Narrower with thinner plates, reinforcing material is added along the top of each link to give the distinctive new side profile. There’s a hard chrome finish and hollow links, with larger diameter rollers that reduce friction and run more smoothly. A lightweight SL version is available with cutout links that saves 7g. Chains are joined with a special new T-Type PowerLock link.

For reference the non-T-Type XX1 Eagle chain costs £89.

AXS Ultimate Controller £215

Weight: 52g with MMX clamp

Older AXS controllers came in left and right specific versions, but the new version can be flipped either side, attached to the brake levers with a Matchmaker X clamp, or the bars with a new Infinity clamp that uses 22.2mm openings at either end. It can be configured in multiple ways to operate the shifting, seatpost, Flight Attendant and, if I was the betting type, potentially the power modes on SRAM’s potential new e-bike motor. The buttons snap on and off, and each press delivers a snappy click that makes it obvious that you’ve instructed it to do something.

For reference the older AXS controller costs £205 and remains compatible with the new T-Type Transmission.

Chainring £100

Weight: N/A Sizes: 34, 36t

Eagle’s new suite of chainrings uses a slightly wider tooth gauge and gets a cool new look, with machined and polished surfaces to match the rear mech. There are multiple options to fit Bosch, Brose and Shimano motors on the e-bike side.

XX Eagle E-MTB cranks £270

Weight: N/A Sizes: 165mm, 170mm, 175mm BB-type: ISIS

SRAM’s latest Eagle cranks cater for both analogue and assisted riders. The crank I’ve been running on my test bike is the XX Eagle E-MTB assembly, utilising carbon arms with a foam core. These are better integrated with the direct mount chainring as the unsightly void is filled by a new plastic ‘Gap Cap’.

There are also carbon XX and XX SL models to fit analogue bikes, but the most interesting and eye-catching crank in the new line-up is the alloy X0 unit. A stunning piece of design, with broad, flat arms, pierced by a large hexagonal aperture near the axle. Machined and polished surfaces reference the mech and give a high-end finish. With chainring and bash guards, the X0 crank costs £320. Talking of bash guards, SRAM has come up with a neat new segmented design that lets you run as much or as little chainring protection as you want.

How it rides

It’s not often you get to ride a new product well in advance of its public release, on trails you know well, without being chaperoned on a carefully choreographed press launch backed up by a fleet of mechanics. But SRAM was confident enough in its product to let me test the new XX drivetrain on a Specialized Turbo Levo e-bike since last October. In that time I’ve clocked up over 700 km and 20,000m of climbing and descending, in some truly disgusting conditions. Maintenance, if you could call it that, has consisted of nothing more than lubing the chain a few times and charging the AXS battery.

So how has it fared? Honestly, it’s been faultless. Although, anything less would be concerning considering the cost. As well as grinding through the depths of winter, I’ve crashed several times, with 22kg of e-bike slamming down on the drive side on at least two occasions. Yet, it still shifts as precisely as it did on day one, despite being battle-scarred, with visible scuff marks on the skid plates.

The shifting itself is – hand on heart – the best I’ve ever tried. Shifts are fast and accurate, even on an e-bike with 90Nm of torque, and over 700W going through the system under load, on steep climbs where you can’t back off the power. It’s particularly smooth when the chain climbs up the block, but even dropping back down under power there’s a really solid engagement. Rejected shifts have been non-existent with the new cassette mapping and X-Sync tooth profiles, and whenever I’ve wanted a different gear, I could get it. On a regular AXS mech, there are times when there’s so much force going through the drivetrain that it actually feels like the hanger twangs and flexes, but the Full Mount has ensured the new mech remains absolutely rock solid, whatever the load.

Operating the system with the new AXS controller is a mixed bag. On the one hand the mounts are more discreet, it’s easier to position them ergonomically, and they’re smaller and simpler. Those buttons also respond with a satisfyingly snappy click. But on rough ground my thumb bounces around on the rubber pads, and that’s caused me to shift two gears when I only wanted to shift one.

Durability really comes into sharp focus when a replacement chain and cassette costs over £700. So far, chain wear is barely registering on my gauge in six months of winter riding, being lubed maybe twice a month. Certainly it’s much less than 0.5%, and SRAM recommends replacing a chain when it gets to 0.8% wear. At this rate – depending on conditions – it should be possible to get 1,600km/1,000 miles out of a chain (on an e-bike) before it needs replacing.

I’ve heard complaints that the chain slaps around a lot as a result of a lack of clutch tension on the old AXS mechs. The new derailleur has a stronger, more damped action. I measured the force needed to overcome the clutch at 3.5kg on the new mech compared to 2.4kg on the old one. As a result, the drivetrain is quieter and smoother, although the extra friction does put more drain on the AXS battery. Even so, I’ve still only had to charge it three times in six months.

One thing I haven’t touched upon is the relative merits of different MTB transmission systems. Mostly because it could be the subject of a feature in itself. But if I’m going to distill my thoughts on derailleurs Vs gearboxes Vs hub gears Vs drivetrains like the Supre Drive, then I would agree that the humble derailleur has its drawbacks. Mostly that it’s vulnerable to damage, but also that it adds unsprung weight, and that the sprockets are all exposed to the elements. Equally, all of the alternatives have their own advantages and disadvantages. It’s a debate that’s been going simmering away for around 20 years now, and yet we’re still waiting for that perfect solution that makes derailleurs obsolete. I’ve ridden various gearboxes and hub systems over the years (I haven’t tried the Supre Drive), and while they did some things better, I still believe the derailleur is the best compromise between weight, friction and shifting under load. As long as mechs don’t bend or break, they’re pretty damn good.

Update after 15-months riding

Plenty has happened since I started testing the T-Type transmission in October 2022, so here’s an update on where we’re at.

Durability

1,200km further down the line, having ridden through two exceptionally wet winters, I’m still on the original chain, cassette, and chainring. Having measured the chain, it is still below 0.5% wear, which is impressive given that it’s fitted to a full power (90Nm) e-bike. With the recommended chain replacement point coming at 0.8%, there is still lots of life in the drivetrain, and there’s no visual signs of damage to any teeth either. Given that a cassette should last two chains, even being cautious and replacing the chain now would see 2,400km from the cassette. It’s entirely possible to run the chain for 1,500km and the cassette for 3,000km given the wear I’ve experienced.

Vulnerability

Midway through the winter after about 12-months riding, I caught the lower cage of the mech on a root on the inside of a rutted left turn. This caused the chain to get caught and the mech was yanked back and out, away from the bike, bending the lower cage assembly. I nursed the bike home in a couple of working gears, but the cage assembly was toast – it’s too difficult to straighten. Fitting a replacement was easy, and the paralellogram, battery, electronics, pulley wheels, and clutch were all undamaged. To replace the lower cage assembly costs a hefty £181 for XX, or you can go for the cheaper GX option and save £60, as long as you can cope with the Franken-mech looks. That’s still very expensive, particularly if you’ve invested in a hugely expensive drivetrain on the basis that it’s going to be more robust. But SRAM does now offer a basic cage assembly, without the clutch, for a much more reasonable £28.99. Since bending my mech, I’ve also seen several other T-Type lower cage assemblies that have either bent or snapped completely on impact. Most of these have been on bikes with a 27.5in rear wheel, as the mech is around 20mm closer to the ground, depending on the tyre.

Shift speed

Shifting from one end of the block to the other, or multiple gears at a time, is significantly slower with T-Type than previous AXS. This is because the mech will only shift one gear at a time, in order to ensure a smooth, precise shift, and reduce drivetrain wear. But the result is that it takes around twice as long (6-7 seconds) to go from one end of the cassette to the other. Hammer in three or four shifts at the AXS controller, and you then have to sit back and wait while the transmission runs through the shifts.