Review: SRAM RED eTap AXS 1x Group
Aug 9, 2019
article & images by Nick Salazar
Continuing from the previous topic of the Quarq, the entire AXS 1x crank is stunning. It's minimal, aero, and the optional Quarq power meter is a big win. You can even start with a non-Quarq and upgrade the ring later. The crank arms are hollow carbon fiber in construction, minimizing total weight.
The crank is available as short as 165mm, and SRAM should be applauded heavily for this. But it would be great to have it in 160mm and 155mm as well. For me personally, I ride 165, so I'm happy. (On that note, why can't someone develop a crank with adjustable length? It would cut down on their own SKUs, and make people very happy. But I digress.)
The spindle diameter is a very odd 28.99mm, matching absolutely nothing else in the industry. SRAM calls this new setup DUB, meaning "Durable Unified Bottom Bracket." It's a bit of an eye-roller for a brand new, not-compatible-with-anything-else standard to call itself "unified," but at least SRAM has properly made a wide variety of new BB cups to work with almost all frames. In short, you can use the new AXS cranks almost anywhere, you just need to buy the appropriate BB from SRAM.
In making the new chainring and BB standards, SRAM is bringing everything into its own ecosystem. SRAM is basically saying to the consumer "the best setup is if you keep everything with all-SRAM parts, no third-party replacements please." It's the kind of end-to-end integration that companies like Apple have championed. It asks a lot of trust out of the consumer, and you really need to bring the goods if you're going to place those kinds of restrictions on choice. Fortunately, SRAM absolutely delivers. Everything here "just works," works brilliantly, and the design choices are absolutely spot-on. I'm happy to sign up for SRAM's setup, given how ideal it is.
Although this group is a concert of parts, an entire symphony of great engineering, the RD has a special place in my heart. If there is one part that I would consider my favorite here, it's the AXS rear derailleur. SRAM has found a unique solution to the problem of 2x customers being the majority, and yet 1x customers being the future. Where the original eTap ignored this progression, AXS definitively solves the dilemma.
Previously, RD movement in a 1x system was accomplished with a clutch system that prevented movement other than the cable shifting, preventing the chain from coming off during road vibration. This works very very well. But it's not compatible with 2x systems, where the front derailleur also changes the tooth count, requiring the RD to move. In a cabled system, there's no way to tell the RD that the FD has shifted. Conceivably, eTap could tell the RD when the FD has shifted, and allow it to let go of the clutch in such situations. But that is not the solution SRAM went for.
Instead, the AXS rear derailleur features liquid damping, which SRAM calles the "Orbit" system. This damping offers a liquid mechanical impediment to the derailleur from moving during high-speed movement like road bumps, keeping things nice and tight and preventing chain drop. At the same time, it allows the spring to move during slower movements like front derailleur action, to keep the system compatible in both 1x and 2x regimes. It's amazing. And it works VERY well. It's rare to find something where everyting on the tin is true, but AXS basically delivers in this regard, especially with the rear derailleur. It is just amazing.
So how is it to set up? Well, as we've described on the last page, it's amazingly simple. There is very little the consumer or mechanic needs to do. Just pair it (as discussed on the previous page), set the limit screws, and go. It works. Extremely well. And the derailleur has up to 33-tooth capacity, meaning there's no real need for additional range sizes. If you desperately need smaller gears, just go for the 2x system and get a smaller chainring. Those go as small as 46/33t, meaning your smallest available gear in AXS is 33-32t, far smaller than ever traditionally available in road gearing. There are no real complaints on range, either in terms of absolute scale, nor in terms of increment. AXS has solved all of this from where I'm sitting.
So right now let's look at the cassette as a feat of mechanical engineering, before we get to the gearing. The new RED AXS cassette bears a fair bit of spiritual responsibility for SRAM. That is, SRAM began as a company making nothing but cassettes, so with any of their groups, the cassette has something of a heritage to live up to. And SRAM does not disappoint. The AXS rear cluster truly is the pinnacle of cassette tech out there, and representative of the journey SRAM has completed so far. This thing packs quite a technical punch. It's made primarily of steel, with an alloy big cog (for the best balance of durability and weight savings). The entire thing is hollowed out, with a level of machining complexity that is absolutely staggering (even for this writer, who is himself a manufacturer of complex products). The tooth shaping makes for flawless shifting, and the small elastomer rings between each gear keep sound to a minimum. And new to AXS, the entire cluster is a single part, no lockring or additional parts. Just this beautiful block of gears.
My 10-33t block came in at 211g, absolutely amazing. Standard cassettes like Shimano's 11-32t 105 will come in at least 110g heavier. Now, 100g here or there won't make a huge difference in terms of your actual race time, but if you want the best, there's simply no substitute. This is it.
This sucker is light, beautiful, incredibly durable, and like everything else in the group, just plain works. Ok, now let's talk about gearing.
12 speeds, 10 teeth
The key to making this system really sing is the new cassette, which features 12 gears, the tallest of which is 10 teeth. That 10-tooth cog lets you run a smaller chainring, which in turn means you'll get a smaller gear on the easy end of the cassette. My group here has a 48-tooth ring, and the cassette is 11-33t. That replicates the range of a 53/39 double chainring, with an 11-27t cassette. Moreover, most of the teeth are tightly-clustered, with a couple big jumps right at the end. This is ideal, letting you really fine-tune your gearing in the middle of the cluster, and then bail out as the hill gets too steep (or you run out of gas). For me (and for the average athlete), I think the gearing options are pretty much perfect. The super strong cyclists out there (pros like Matt Russell) would benefit from going up to the 50t chainring, which SRAM makes. Athletes who find the 48t is too steep can size down to 46, 44, or even 40 teeth, although these smaller sizes don't have the nice aero shaping.
Now, let's talk about efficiency. Lots of great math and analysis has been posted elsewhere, and different people come to different conclusions. Those who decry the 10-tooth cog complain that it comes at a cost of efficiency in the system, to the tune of a couple of Watts (I've read anywhere from 1 to 6 Watts lost compared to an 11-tooth cog). However, I find this an incomplete story. First of all, keep in mind that dropping the front derailleur and small chainring could (and in my testing, DOES) represent a wattage savings which can offset any mechanical loss by adding a 10-tooth cog. Moreover, that savings will be enjoyed throughout 100% of your ride, while the mechanical loss only applies while you are actually in the 10-tooth cog, which is maybe 10% of your ride or less, depending on route. So, that would suggest that the aero savings need be only 10% of the magnitude of the mechanical loss for them to offset one another. That is, even if a 10-tooth cog costs you 10 Watts (10 percent of the time), and dropping the front derailleur only saves you 1 Watt (all the time), those offset one another. I'm confident that in reality, the disparity is far less, meaning that there is, in the end, a net efficiency savings.
What about going smaller-toothed cogs? Is a 9-tooth cog worth the trouble (and additional loss in mechanical efficiency)? From where I'm sitting, with the available gearing, 9-tooth cogs are not a necessity. I think for the vast majority of athletes, 10-tooth cogs with the appropriate chainring will do just fine. But more important is the fact that 9t cogs can finally exist, thanks to SRAM's innovation in this space. I predict that the 10t cog will reign supreme over 11t or 12t, regardless of the athlete. More important that the size of the smallest cog will be the size of the chainring, and the actual cassette range.
To put it simply: AXS is absolutely excellent, and is the first group to make it ideal to switch to a 1x setup.
In the new Wild West of disc brakes proliferating in road cycling, one of the most common questions I've gotten about the new AXS group is: can I still use it with my trusty rim brakes? Or do I have to move to a disc brake platform? There's nothing about AXS that mandates the use of disc brakes. Nor even do you have to use SRAM brakes. The shifting hardware is completely decoupled from the brake levers, meaning you can use any brakes, any brake levers, of any type. You just add the Blips as the last step. I still prefer Shimano's BL-TT78 and BL-TT79 levers for use with rim brakes, they're what we always recommend for use with our Omega X brakes. So regardless of what bike you have, whether it's brand new or ten years old, there's nothing preventing the use of AXS on your ride, except of course the fact that you need the new XDr freehub body on your rear wheel, as already mentioned. Even on the road side, SRAM makes levers for either mechanical rim brakes OR their new hydraulic discs. End of the day: yes, you can use any brake you like with AXS.
Hit the jump and we will wrap up the review of this beautiful group.
Individually, each AXS component is strikingly beautiful, especially the cassette and the crank. Here are some up-close looks at the parts themselves.
Our Test Rig
We set up our AXS group on an Omni, which can use a 2x setup, but is right at home with this 1x group. On Omni, the front derailleur hanger can be removed, and replaced with a small plate that completes the aero shape of the frame, leaving nothing for the wind to see.
Front End Details
Front end: we mounted the BlipBox on the underside of the Alpha One's Dragonfly, using the M4 threaded hole already on the BlipBox. No mods needed, and it keeps everything absolutely clean while still easily accessible. Please forgive the messy-looking arm cups. Those are our new prototype Scoops, just a 3D print with some hand-cut pads. Bar tape is Silca: Nastro Fiori on the extensions, and the slightly thinner Nastro Piloti on the base bar. This is easily the most comfortable front end I've ever used, and shifting feels awesome on the AXS clics.