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The new Specialized S-Works Aethos is more than just crazy light

Race it, or don't. The bike by the Morgan Hill, Calif.-based company gives you high performance for any type of ride you want to do

Specialized S-Works Aethos Shimano Dura-Ace Di2. Photo by: Nick Iwanyshyn

The Specialized S-Works Aethos has been a bad secret by design for a few weeks now. In mid-September, Bora-Hansgrohe rider Daniel Oss put out a picture of the new bike on social media. It has fairly skinny tubes and a sharp paint job called satin carbon/red gold chameleon/bronze foil.

Specialized says the bike is not for racing, yet it has a UCI-approved sticker. The Aethos is crazy light. A size 54 frame built with the company’s top-end FACT 12r carbon-fibre mix is 575 g. (That’s with the lightest paint job.) The Shimano Dura-Ace Di2 model comes in at 6 kg. My scale reads 6.19 kg. All these numbers say this bike is too light to race. Remember, the UCI’s minimum weight for road bikes is 6.8 kg.

The branding on the Aethos is subtle. There’s little on the frame that tells you who the bike is by and what its name is. You’ll see the big S on the head tube, a small “S-Works” on the top tube and “Aethos” on the inside of a fork blade. The paint schemes are solid, mostly dark, and precise. As recently as just before the start of the Giro, I would have said the bike had been “Rapha-fied” or marked the “Rapha-fication” of its look. With the recent EF/Rapha/Palace collaboration—well, that’s not the visual vibe of the Aethos at all. It’s regular raphafication.

The Aethos, though, is a bike that Specialized has positioned in a—shall we say—a slightly alternative category. You can race it, but it’s not specifically designed for that. It’s a cutting-edge, high-performance machine, that you should ride anyway you want.

Specialized S-Works Aethos Shimano Dura-Ace Di2
A UCI sticker means you can race the bike. But, it’s so light that you might need to tweak it before you roll up to the start line. Image: Nick Iwanyshyn

Development of the Specialized S-Works Aethos

Work on the Specialized S-Works Aethos began soon after the launch of the Tarmac SL6, roughly four years ago. Specialized engineer Peter Denk spent a lot of time examining how forces were transferred through the SL6 frame. He started to suspect that forces don’t move through the tubes as we traditionally believe. “Usually, we have a big down tube and most of the time we have big chainstays,” Denk says. “We have a big bottom bracket to make it stiff. We have a smaller top tube and seatstays. These are kind of the industry standards of how we design frames. That makes sense if you think all the forces flow through the bottom of the frame, that the main beam is down tube/chainstays while the BB is activated by the rider. But looking at that frame, I thought maybe something totally different is going on. Maybe the forces flow in a different path through the frame.”

Specialized S-Works Aethos Shimano Dura-Ace Di2
A barrel-shaped head tube joins to top and down tubes that taper as they run rearward. Image: Nick Iwanyshyn

Denk noticed that when the Tarmac SL6 frame was under a pedalling load, provided by a pedalling machine, there was more twisting at the head tube than he expected, which affected the top and down tubes. His solution was to make a barrel-shaped head tube. From there, the top tube got beefy where it connected with the head tube, and it was the same for the down tube. They both taper to a narrower diameter as they extend back toward the rear of the bike.

If you give the Specialized S-Works Aethos a quick glance, you may not notice how different the tube shapes actually are. But next to the Tarmac, for example, you’ll see the Aethos has more traditional seatstays. The bottom bracket of the Aethos is quite svelte as well as the down tube. If it weren’t for the sloping top tube, the frame would look pretty traditional.

Specialized S-Works Aethos Shimano Dura-Ace Di2.
The Specialized S-Works Aethos has traditional-looking seatstays. They and the front fork offer clearance for tires as wide as 32c. Image: Nick Iwanyshyn

According to Denk, there’s a lot going on at the joints. “We optimized all the joints so the forces can flow through the frame like water,” he says, quite poetically. “As a result, we hoped, that we could take out a ton of reinforcement fibres and all of the stiffness fibres because, we thought, with this shape [of frame], the stiffness will come 100 per cent just from the shape and we don’t need so much reinforcement in the joints because the fibres flow so well.” One of the first prototype frames came in at 560 g. It passed, according to Denk, 70 per cent of the necessary testing. It wasn’t much further to go to today’s Aethos frame.

The engineer stresses that the thickness of the tube walls wasn’t reduced. The tube walls are just as thick as the old SL6. It’s just that the tubes have narrow diameters, hence a lot of the weight loss.

Specialized S-Works Aethos Shimano Dura-Ace Di2
Image: Nick Iwanyshyn

One of Denk’s comments that I found fascinating was with regard to frame stiffness. “We like it very much if we have a little bit more stiffness in the front than in the rear,” he says. “We also like that the deflection is linear. We like a linear, predictable stiffness. We want a certain stiffness in the frame to give you the best possible feedback on cornering and braking.” I hear a lot about tuning the stiffness of carbon-fibre bike frames from various builders. To me, it often seems like an abstract exercise. But Denk reveals that it’s almost a matter of taste. Sure, a taste or sense that comes from testing and experience, but a judgement call nonetheless from a designer.

Features of the Specialized S-Works Aethos

The Specialized S-Works Aethos I tested was the Dura-Ace Di2 model. It came spec’d with the Specialized power meter. It has a Canadian connection. It’s been developed through a partnership with 4iiii, a Cochrane, Alta.-based company. The stem and bars are traditional, that is, not integrated. Making changes is a breeze, as is dialing in your fit.

Specialized S-Works Aethos Shimano Dura-Ace Di2
The Specialized S-Works Aethos Shimano Dura-Ace Di2 has a power meter designed in partnership with Canadian company 4iiii. Image: Nick Iwanyshyn

The frame is made of Specialized’s top-end carbon-fibre recipe: FACT 12r. It can only accommodate electronic groupsets. It’s durable, too. Denk says you can sit on the top tube for the pro-casual look when you are waiting at a stoplight. But, as with any carbon-fibre frame, don’t clamp it in your workstand. There’s clearance for tires as wide as 32c, so you can run some treads that will keep you planted on gravel.

The frame comes with a new type of seatpost by Specialized house brand Roval, called the Alpinist. It has a diameter of 27.2 mm and comes in lengths of 300 mm and 360 mm. It’s offset is 12.5 mm. Also bearing the name Alpinist are the Roval Alpinist CLX wheels.They weigh in at 1,284 g. The bike uses a threaded 68-mm BSA bottom bracket. You saw this development on the new Tarmac. I’m a fan of it on both bikes for its solid, creak-free performance.

The Specialized S-Works Aethos Shimano Dura-Ace Di2 rolls on Roval Alpinist CLX wheels. Image: Nick Iwanyshyn

Even the humble thru-axles received attention. Specialized’s previous set of lightweight axles weighed 67 g. The Aethos’s axles weigh 53 g. In comparison, a single thru-axle is close to 90 g. Specialized got a little tricky around the front fork. The disc brake caliper (the frame is disc-brake only) is set on a Specialized-designed mount. This mount allowed the designers to take out a good bit for carbon-fibre from within the fork. The amount of carbon around the bottom half of the front axle seems alarmingly little.

First ride impressions of the Specialized S-Works Aethos

The Specialized S-Works Aethos feels a lot like the new Tarmac, which isn’t a surprise as the two bikes share the same geometry. It rewards a rider who can get low and in the drops. The Aethos, however, has its own feathery characteristics. Man, is it light. So, you won’t be shocked when I say it’s an absolute joy on climbs. Screaming downhill and through corners, it behaves exceptionally well. I would say that’s a feature of Denk’s linear deflection in the frame. You feel confident and in control at speed in a straight line or in a curve.

The Aethos is a far-out high-performance bike. Ride it anyway you want.

Specialized S-Works Aethos, Shimano Dura-Ace Di2, $15,299, specialized.com/ca

Specialized S-Works Aethos Shimano Dura-Ace Di2
The front disc-brake caliper has a Specialized-designed external mount. The mount allows designers to shave off carbon fibre within the fork. Image: Nick Iwanyshyn
Specialized S-Works Aethos Shimano Dura-Ace Di2
Image: Nick Iwanyshyn
Specialized S-Works Aethos Shimano Dura-Ace Di2
Where’s the name of the bike? Oh! There is on the fork. Image: Nick Iwanyshyn
Specialized S-Works Aethos Shimano Dura-Ace Di2
A Shimano Dura-Ace Di2 derailleur moves the chain across the cassette. Image: Nick Iwanyshyn