The Perfect EMTB Gearshift?
Sram Eagle Transmission Review

With the SRAM GX Eagle Transmission, the cutting-edge X-Type technology trickles down to more affordable price points. We delve into what the new SRAM GX Eagle Transmission can do and compare it to the traditional AXS and the mechanical GX Eagle variant. Is the upgrade worth it?

With the introduction of the SRAM 12-speed Eagle groupsets, SRAM has taken technical supremacy in the market. Even though Shimano, the largest supplier in the bicycle industry, countered with a 12-speed offensive, the innovations in the mountain bike drivetrain sector are currently coming out of Schweinfurt. Period.

The latest unveiling of the SRAM XO and XX Eagle Transmission showcases once again that Shimano currently has little to offer against SRAM when it comes to mountain bike innovations.

The team at Sram, after laying the front derailleur to rest, have now also done away with the derailleur hanger. The new T-Type drivetrains are robust, offer modular repair options and eliminate the tedious fine-tuning.

Despite these advancements on multiple fronts, there was notable criticism at launch. Sram was accused of digging too deep into consumers’ pockets for these innovations. The Transmission drivetrains, which bolt directly onto the frame without a hanger, were seen as too expensive by riders everywhere.

However, with the GX Eagle Transmission, there is now a more affordable version that retains nearly all features of its higher-end siblings. Will this derailleur quell the critics in the scene?

Before you balk at the price of SRAM Transmission drivetrains, it’s crucial to understand what you’re actually paying for. SRAM’s replacement of the derailleur hanger, the traditional link between the rear mech and the frame, is not without purpose. The goal is clear: the engineers from Schweinfurt are on a mission to improve shifting performance. For eMTBs, achieving better shifting under full load was a key development target.

To upgrade the already stellar performance of the Eagle drivetrains, SRAM targeted the crux of the matter – the derailleur hanger. When SRAM rolled out the UDH (Universal Derailleur Hanger) with considerable force, it was evident that the ambitions went beyond just creating a global standard for spare parts.

This UDH hanger standard is ultimately the prerequisite for mounting the new SRAM Transmission derailleurs on your bike. Unlike traditional (non-UDH) hangers, the UDH doesn’t just connect the frame and the rear mech.

It also includes the threading for the rear wheel’s thru-axle. With this innovation, the position between the rear axle (including the cassette) and the rear mech is permanently and precisely determined.

Once it’s clear where the derailleur sits in relation to the cassette, all stops and gaps can be precisely adjusted right from the factory. Manually adjusting the high or low limit screw on the new Transmission drivetrains is so redundant, there are no longer any adjustments for this.

The same goes for the gap between the upper jockey wheel and the cog, which had to be adjusted using a somewhat fiddly plastic gauge on all Eagle drivetrains up until now. To put it another way: SRAM’s Eagle Transmission derailleurs are perfectly tuned right out of the box. Thanks to the defined connection between the thru-axle and the derailleur, all variables are eliminated, along with a lot of work for mechanics.

SRAM improves shifting quality with a flawless factory setting. Combined with the electronic drivetrain, which precisely defines the parallelogram movement of the derailleur and pivots it from cog to cog, there’s simply no such thing as a misaligned shift anymore. That’s because there’s no longer any variance in the tension of a mechanical cable.

T-Type drivetrains have simply eliminated any pitfalls one might encounter during installation or adjustment. The Transmission drivetrains remove complexity from the equation of shifting for the end user. For this, we must thank SRAM. The complete installation of the groupset is manageable even for the less talented wrench in under 30 minutes. The only new feature, compared to traditional Eagle drivetrains, is that the chain can no longer be sized live. The exact chain length must be determined via an app or online calculator. No app is necessary to pair the shifter and derailleur.

For many, the derailleur hanger was not a nuisance over the decades, but a deliberate designed breaking point between the frame and derailleur. If a branch gets caught in the drivetrain and bends or snaps off the hanger, as a rider you can buy a new derailleur hanger for 10 – 20 euros and repair the entire bike.

Frames and derailleurs often survive such encounters on the trail without damage if the energy is dissipated by the derailleur hanger. Of course, the question remains: Where does the energy go in such cases if there is no derailleur hanger?

So let’s say a virtual stick gets caught in the derailleur. What happens?

Scenario 1: Holding the derailleur in your hand, its robust construction is immediately evident. There’s none of that flimsy back-and-forth wobble that you might remember from old 9-speed derailleurs. Instead of thin plates, the parallelogram is made of substantial, confidence-inspiring arms. Looking at this derailleur, the answer to the previously posed question springs to mind: The stick is more likely to break.

Scenario 2: If the stick or obstacle doesn’t break, of course, the derailleur also features the “Danger Function” just like its AXS predecessors. In this case, the derailleur senses an external impact and recognizes it as such. The mechanism receives a signal to momentarily yield in the direction of the spokes to prevent any damage. Afterwards, the derailleur repositions itself correctly.

Scenario 3: If the first two scenarios fail, could it be conceivable that the frame gets damaged? This is unlikely, as the derailleur is primarily mounted to the thru-axle, not the frame itself. And a 12-millimeter thru-axle usually doesn’t bend, even under significant forces.

It’s more probable that the derailleur itself would be the part to break. Transmission derailleurs are not indestructible after all, but they are (for the first time in the history of derailleurs) highly modular and repairable even without specialized know-how.

The derailleur cage with its two jockey wheels can be swapped out without any tools. Of course, you can also replace the jockey wheels individually. Additionally, the outer arm of the parallelogram can be replaced by a non-expert using just two 2.5mm Allen screws.

The drivetrain is protected by a plastic cover, which can also be replaced with a single screw. With five additional screws, the part of the derailleur that attaches the mechanism to the frame can be exchanged.

SRAM’s factory service is even capable of replacing the rear arm of the parallelogram or the mount for the derailleur cage’s clutch. Essentially, the derailleur has been engineered like a partially replaceable cage around the gearing system. The prices for spare parts are currently still high; however, in the future, it’s conceivable that third-party providers could enter the market to offer repairs at lower costs.

One installs the groupset. One hops on the bike. One expects greatness, but the wow factor is missing. Because the derailleur shifts. It does what it was designed to do. Between “pressing the shifter” and “changing gears”, there’s a minimal delay.

But that’s now par for the course with all electronic shifters. What’s new, however, is the significantly improved tactile feedback of the POD controller (this is the name for the T-Type shifter) when compared to the old AXS controller or Rocker Paddle. Thanks to the pronounced tactile response, you’re not accidentally shifting one gear too many or too few. After some initial gentle experimenting, as a test rider for the new groupset, you start to really give it some welly.

Can the newcomer handle a shift under full load? Easy! For decades, I’ve trained myself to ease off the pedal for a quarter or half a revolution immediately after pressing the shifter. That’s actually unnecessary with the new extremely stiff setup. This is especially true for the use of the groupset on an E-MTB, as the motor applies multiples of human power.

The engineers seem to have taken into account the increased use of e-bikes as well. Of course, with the app, you can customize various preferences: button function assignments, shifting multiple gears with just one button press. Neat features. But we were quite happy with the factory setup. After about 30 hours of ride time, the battery indicated that it needed recharging. However, the battery was not completely depleted during our testing.

Even though the battery life is really good, there’s something about a mechanical cable that feels more independent. Can’t help but get a bit nostalgic. Otherwise, the real advantage of electronic shifting becomes apparent when conventional systems start to become a hassle. That mandatory tension adjustment of the shift cable on a new bike is no longer necessary.

And besides, there should be no need for any kind of readjustment anymore. (There are no mechanical screws for readjusting anything. Fine-tuning of the derailleur position can still be done electronically in increments of a tenth of a millimeter, but it wasn’t necessary for us).

We’ve taken the time to weigh each component listed in the table below ourselves. As expected, the more budget-friendly GX Eagle drivetrain is approximately 350g to 150g heavier than its pricier counterparts, the XX1 Eagle and X01 Eagle groupsets. Surprisingly, there’s a significant weight gain of 201g when compared to the mechanical SRAM GX Eagle groupset.

This is primarily due to the crankset with integrated bashguards. If you remove these, you save exactly 80g. When you add the weight of a full-length shift cable housing and derailleur hanger, and consider the bashguard, the GX Eagle drivetrain is exactly 40g heavier than its mechanical equivalent.

The extra weight is within an acceptable range. For those looking to shave off grams, you’ll have to dig deeper into your wallet for the XX1, X01, or the XX1-SL versions of the drivetrain components.

To establish a comparable baseline for this article, we’ll refer to the MSRP offered by SRAM or Shimano. Of course, we know that prices will already be about 15-20% lower in popular online shops just a few days after their launch. It’s always the case. Thanks to the free market economy for this effect.

The GX drivetrain isn’t cheap, but it’s significantly more affordable than its big siblings (the XO and XX drivetrains). The complete groupset will soon be available for under 1000 €. It’s no bargain, but for a brand new, revolutionary, and durable technology, it’s still OK. The price for the wear bundle, including chain, cassette, and chainring, is also acceptable. With a nickel-coated chain and cassette, the durability of the GX Eagle T-Type components is expected to be similar to that of the legendary XO Eagle groups.

Time will tell. We cannot make any statements on this yet. What is noticeable: The bare aluminum spots, like those on the XO Transmission, are not present on the GX version. Scratches or wear on the crank arm will be much more visible. However, the silver finish of the cassette masks signs of wear significantly better than the old GX Eagle cassettes.

At the functional level, it’s only worth mentioning the absence of the Magic Wheel in the GX Transmission compared to the XX or XO versions. The jockey wheel doesn’t continue to spin when you stick a branch into its openings. However, you can retrofit this feature.

We mentioned it at the outset: SRAM currently undoubtedly holds the technological lead in E-MTB drivetrains. This won’t shake Shimano’s market dominance as the world’s largest component manufacturer, but it will certainly unsettle the Japanese in Osaka.

In the medium term, they’ll have to counter Schweinfurt’s innovation and development pace with something. But what? Bike manufacturers have agreed on the UDH standard for derailleur hangers. It will be embarrassing if Shimano starts adopting it, but it seems inevitable. Shimano also has yet to demonstrate anything in the realm of wireless shifting with decentralized batteries.

To pull off a stunt, they would need to either introduce a 13-tooth cog on the cassette (which is somewhat redundant for performance riders) or unveil an electronic shifting system sans batteries. There are patent drawings of electronic shifting systems that draw their energy from a dynamo in the jockey wheel.

However, these drawings are still very abstract. It is more likely that Shimano will soon present a well-repairable direct-mount derailleur hanger at a significantly lower price point than SRAM. That’s how they’ve played it recently. They let SRAM do the pioneering work and later reclaim their market share through attractive pricing.

Beyond the market leaders in mountain bike drivetrains, there are also alternatives from smaller providers. TRP and MicroShift strive to emulate the gear-shifting systems of the big brands as closely as possible.

Lal Bikes from Canada is entering the race with a significantly more innovative approach. Stemming from the idea that a derailleur shouldn’t be so prominently positioned on the frame, they’ve reimagined the chain shifting system entirely.

The derailleur cage, which ultimately maintains chain tension, has been separated from the derailleur and installed as a separate component near the crankset. The derailleur parallelogram is well-protected within the rear triangle of the frame. Currently, this shifting system is available for purchase in combination with a Nicolai Bike.

We’ve already had the opportunity to test ride the system and will be publishing an article on it soon. If you’re interested, simply sign up for the newsletter below. For now, we’ll only reveal this much: it works, but there’s still room for improvement. Why did we mention it in this article, then? Because it impressively demonstrates that innovation in cycling knows no bounds.

It’s quite possible that drivetrains on e-mountain bikes will change again in the next 10 years. More and more manufacturers of e-bikes are starting to combine motors with transmission systems. There’s more potential in the market than one might think.

Pinion has revolutionized the classic derailleur system for e-bikers with its Motor Gearbox Unit (MGU), by integrating a gearbox directly into the motor. Instead of simply adopting the tried-and-true from traditional bicycles to eMTBs, it definitely makes sense to completely rethink the concept of gearing on electric mountain bikes. We’ll soon be putting this new transmission to the test. Sign up for our newsletter in the footer to ensure you don’t miss out on our test results.