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Sep 17, 2023

SRAM Eagle Transmission Improves Modern MTB Drivetrains, but Don't Rush to Upgrade

In the bicycle world, SRAM’s Eagle Transmission is a big deal, though I think

In the bicycle world, SRAM's Eagle Transmission is a big deal, though I think it's still hard to say exactly why. The last two major MTB drivetrain advancements happened during my tenure as a mountain biker. I’m roughly ten years old to this sport now, but in that time frame, bikes went from 3x to 2x to 1x, eliminating the unnecessary front derailleur.

Then, we were at 1×11, giving us a wide range, with SRAM cassettes offering 11-42t gearing and Shimano's 11-speed at 11-46t. I was proudly using one of those trusty Shimano 1x11s on a bike up until last year.

Then, of course there was the 1×12 race, with SRAM arriving first with a 10-50t, and Shimano sliding in with a 10-51t. Not to be outdone, SRAM later showed up with the 10-52t cassette in an update. That was three years ago in June of 2020 with an update to the entire Eagle range, including the AXS line. And then, we waited. What more does a mountain bike drivetrain need? We had electronics, 520% range, and wireless/bluetooth shifting. While Rotor and Campagnolo dropped 1×13 groupsets, it still seemed unnecessary for mountain bikes.

With the move to the Universal Derailleur Hanger, spy shots of direct mount drivetrains, and then third-party direct mount conversion kits, it all started to make sense.

SRAM released the all-new Eagle Transmission near the end of March, discarding the "drivetrain" nomenclature with the derailleur hanger. It's silly marketing speak, if you ask me, but maybe it's a play on the fact that bluetooth transmits signals from one device to the next and the words drivetrain and transmission are roughly synonymous.

Currently, the SRAM Eagle Transmission line includes a fully electronic drivetrain with either the X0 or XX label, meaning that they are the highest shelf drivetrains the brand offers. While there were a number of updates to SRAM's cassettes, chains, crank arms, and shifters, the biggest news is that it did away with the derailleur hanger.

It's hard to say what took so long, other than the nature of these meetings between one or two component manufacturers and the dozens and dozens of bike brands that need to be convinced to adopt a new standard before it's released.

But there are clearly benefits to ditching the hanger. I can only speak for myself, but over ten years and I’ve never hit a derailleur hard enough to actually need one of the dozen spare hangers I’ve collected throughout the years. Of course many people have. But the logic of having a really tough rear triangle and a really tough derailleur connected with a piece of material that is meant to bend or break and needs to be checked every time shifting is sub-par.

By getting rid of the hanger, it means that it should be easier to set up flawless shifting since there aren't any adjustment screws.

My first impression of the SRAM X0 Eagle Transmission derailleur is how much bigger it is than their other derailleurs. X0 and XX Eagle Transmission derailleurs weigh 80-90g more than their indirectly mounted counterparts.

SRAM built some armor into the new derailleurs with a skid plate and a revised orientation that keeps the top pulley wheel aligned with the cassette and the cage pointing toward the chainring. In the event the derailleur is impacted and damaged, it is supposed to be rebuildable with replacement parts.

The derailleur also gets a "magic wheel," a lower pulley wheel that will keep rotating even if it's jammed up with a twig.

A big portion of shift quality comes down to the interface between the chain and cassette and SRAM revised both, moving to the X-SYNC tooth profile, even stating the harder that someone pedals, the better it shifts. The teeth have a narrow-wide profile like most 1x systems and the Transmission also utilizes the T-Type Flattop chain, which SRAM says makes it stronger, more durable, and optimizes shifting.

SRAM has only made 10-52t cassettes for Transmission at this point and there are three different options; an X0, XX, and XX SL.

It's worth mentioning that SRAM's Transmission chainline is 55mm, up 2.5mm from 52.5mm. The cassettes still use an XD driver, but the gears have been moved outboard slightly, with the hope of improving chainlines and minimizing wear and drag.

The shifter, or as SRAM calls it, the AXS Pod Controller, was updated too and it has a more controller-like look and feel with two distinct buttons rather than the old design, which sort of mimicked the feel of a mechanical lever. It's still customizable and is lighter than the previous version.

Cranksets were updated too of course. Carbon XX SL and XX cranksets look like most carbon cranksets while the X0 takes on a new look with a middle section carved out of the arms. The X0 crankset is made from aluminum and optimizes stiffness and weight. The X0 and XX cranks have 165mm, 170mm, and 175mm lengths, while their e-bike versions have 160mm options.

All of the new Eagle Transmission components have formed their own ecosystem and aren't backward compatible with older Eagle components according to SRAM, and older components are not forward compatible. At the entry-level price point, which is $1,600 for an X0 crankset and chainring, a derailleur, cassette, chain, shifter, and battery and charger, it's a steep barrier.

However, let's not forget how SRAM has rolled out new products in the past. When the brand first released AXS electronic shifting, it was only available with the XX1 and X01 labels in early 2019 and it wasn't until nearly the spring of 2021 when they added a GX option for electronic shifting. The same thing happened with 1×12 mechanical shifting in 2016. The brand focused on its top-tier lines before releasing more affordable options. There's also no apparent reason that direct-mount shifting needs to be exclusively electronic. So while the latest drivetrain options are pricey, there's hope still.

We received a Revel Ranger test bike with an X0 Transmission when the bike was released a few weeks after Transmission. We spent a few weeks on the bike riding in spring Colorado conditions and being as hard on the drivetrain as we could be.

We also spent a few days on the latest Pivot Mach 4SL before the bike was released, which had the XX version installed. Between the two, we likely got close to 200 miles on the drivetrain and though we can't talk about long-term durability, it was a great way to get acquainted with the performance of the groupset.

Since the drivetrain came already installed on a test bike, really the only thing I had to worry about was charging a battery and dialing in the cockpit. After that I was spinning around my neighborhood, snapping through gears and planning trail rides.

Off the bat, setup wasn't any different than an older AXS group and the drivetrain worked seamlessly right away. Immediately, it was hard to tell a major difference in shifting performance between Transmission and older drivetrains until I got on the trails here and could feel it in action, up the steep hills and down rocky trails.

While the shifts feel familiar to any SRAM drivetrain, with quick, crisp shifts, I’d say the shifting feels noticeably improved… and distinctly SRAM. I can't say that the X0 Transmission felt faster than say the X01 AXS drivetrain, but it does feel smoother, more precise, and responsive. Maybe the new feeling comes from deleting the hanger for a stronger interface, or maybe it's the X-SYNC profile, or a bit of both, but it's a stellar-feeling drivetrain.

Transmission takes heavy shifts in stride, as it promises. This comes in handy in drainages in particular, when you’re entering a ravine in a high gear and need to drop a scoop of gears all at once. Unfortunately the Pod Controller doesn't allow for multiple downshifts with one press like a mechanical shifter would, but you can still smash the button multiple times very quickly. The Transmission can be a little vocal with these shifts at times, but it finds the right gear under load and settles in very smoothly.

I can't say I like the new shifter… err controller pod as much as the previous "paddle" version. The latter was easier to get where my thumb likes it, whereas it felt more difficult to get the pod around the brake clamp to somewhere I liked. Both bikes I rode though were set up with a separate clamp however, rather than mated to a brake lever with Matchmaker.

On some of my last days with the X0-equipped Revel, I raced 18 Hours of Fruita, netting five laps, or roughly 35 miles in the high desert's chalky moon dust. My first laps were at midnight and then 5:45 a.m., so I went right back to sleep, but later in the day I noticed everyone spraying the silt off of their drivetrains after every lap. Sorry, Transmission, I said. You haven't earned the wash yet.

There were some rattly, bucket-of-nuts noises coming from a lot of bikes that day, and though the dust posed somewhat of a challenge to the Transmission, I didn't have any pronounced shifting problems at the end of the day, aside from the derailleur not wanting to stay in third gear. This had popped up before the race. I downloaded the AXS app when I got home and within about five minutes, I tuned the derailleur and it was shifting flawlessly again–and even better after a rinse.

Between the X0 and the XX, which is a $450 difference, the XX has a slight edge. The derailleur looks more refined, the cassettes are lighter, and the crank arms more carbon. And it is the slightest bit faster than X0. Over the course of two days in Cortez on the new Pivot, we ran into a little mud, but it was mostly dry, buff desert conditions.

Last year I took advantage of a deep sale on an Ibis Ripley AF frame. With the bike having been released fairly recently, I wasn't worried about buying a bike that was almost on to a new generation, but I did question the discount.

When Ibis rebranded, the new frames got the new badging. I thought I’d saved $500 on a frame for a different paint job, but they also moved the rear triangle to UDH, thus making it compatible with SRAM direct mount tech, and making my new bike incompatible with the tech.

When I told friends that I’d been riding the Transmission, they also surmised, "I guess my bike is obsolete now." It's hard not to feel that way when the majority of new frames are moving to a new standard, but I have told friends, I don't believe it's worth selling your current bike just to get the newest drivetrain technology. Still, it's natural to feel excited about getting a new bike if you happen to be at that stage.

As a whole, SRAM's Transmission is a noticeable improvement in shifting over its previous drivetrains, but not something I’d call game-changing performance. I’ll qualify that and say that it's a wise direction to head for drivetrain progression. Why not have a stiffer, stronger, better system by removing the hanger and improving the chain and tooth interface? And as noted above, it's more likely than not the technology is going to come down to other price points.

There's a lot to digest with the launch of SRAM Eagle Transmission. Over 200 frames and numerous brands have been convinced to implement SRAM UDH, so there is obviously a lot of buy-in, and rumors of Shimano direct-mount technology have been swirling too.

Eagle Transmission provides fast, precise, and reliable shifting on sunny days and on rainy days, and it's undeniably a great move for modern mountain bike drivetrains. But you also don't need it and shouldn't feel compelled to sell your bike to keep up with the Joneses. After all, it’ll probably be here a while.