585g Specialized Aethos is the newest World’s Lightest Road Bike.

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“What if we built a bike that’s simply for the love of riding?”

That was the idea behind the all-new Specialized Aethos, a bike that started as a simple concept and ended up “breaking the rules of designing bikes.”

Where a bike like the Tarmac is clearly purpose built for winning races, the Aethos is a road bike that’s made for the everyone else. From the outside, it’s painfully simple, with smaller logos, threaded bottom brackets, more subtle paint schemes and user-friendly features.

Oh, and it’s the lightest bike they’ve ever made.

In fact, they say it’s the lightest disc brake road bike ever produced. By anyone.

How Specialized Aethos became the lightest road bike

We know you want numbers, so we’ll start with the complete bike. They say you can easily get to a 5.9kg (13.01lb) complete bike weight with a normal, everyday build. Well, a high end build, but with standard off-the-shelf parts.

specialized aethos is the worlds lightest road bike

It’s their most technologically advanced bike. It’s a high performance road bike that’s not focused on racing.

Which is such an odd concept that their road and gravel product managers had to start the project in secret because they weren’t sure it would get buy in from management.

specialized aethos s works road bikes leaning against a wall
Photo: Chris Auld for Specialized

The idea started years ago, when they first started working on the Tarmac SL6. Specialized said with that model, and the subsequent SL7, the priorities for those models were shifting further and further away from the priorities of everyday riders like you and me.

Meaning, they were becoming almost exclusively focused on racing. But the goal for regular riders? Just “The Perfect Ride”. So, that became their goal for the Aethos.

But where to begin? In the lab of course.

detail photos of the specialized aethos s works road bike

The traditional way of thinking about design is to create an oversized downtube and BB section to maximize power transfer, and smaller, thinner tubes up top to enhance comfort. But as their engineers zoned out watching the frames on the test equipment, they noticed that a lot of the “bad” flex was coming from twisting at the head tube. They were intrigued.

fea simulations screenshot showing stress zones on a bicycle frame during pedaling

So they started tweaking virtual models, created 100 different shapes, sizes and layups for each part of the frame. Then they started combining them. Testing for acceleration, cornering, braking, and all the other forces a frame is subjected to. All told, it was the equivalent of 100,000+ different frames tested in computer simulations over 16 weeks.

From there, they filtered it down to 20 iterations, with key points of interest being upper and lower sections of the seat-, top- and down tubes, and the fork crown. And then they built up test mules to actually ride them. Because that’s the one thing a computer simulation can’t do (yet)… tell you how well it’s actually going to ride when the rubber meets the road.

detail photos of the specialized aethos s works road bike
That’s right, a standard threaded bottom bracket!

Once they got the shape where they wanted it, they started messing with layups. The first real prototype came in at just 560g and could pass 75% of their tests. Which, to them, said that the shape worked extremely well. And that every fiber was under tension at the intended loads. Meaning, no “lazy fibers” serving no functional purpose.

aethos frame stiffness and layup heat map showing carbon fiber placements
Full frame shows minimal overlap or extra “stiffness” layers used on the Aethos. In contrast, the darker red and orange areas in circles represent extra material used on other frames.

In some bicycle frames, they say as few as 60% of the fibers are handling a load. On the Aethos, about 95% of the fibers are directly under tension. And they didn’t have to add very many fibers from that first prototype in order to achieve this.

detail photos of the specialized aethos s works road bike

After a few more tweaks, they had a frame that could pass all their tests and rode splendidly. Final weight? A size 56 S-Works level layup with Satin Carbon/Jet Fuel finish, comes in at an average of 585g +/-5g.

Average claimed production, painted weights for all Aethos S-Works frame sizes are:

49 52 54 56 58 61
550g 565g 575g 585g 623g 643g

detail photos of the specialized aethos s works road bike

And that’s with standard standards, virtually no integrations or weird, proprietary parts. Seriously, it has:

  • BSA threaded bottom bracket
  • standard tapered head tube
  • standard round seatpost and clamp
  • 32mm tire clearance
  • 125kg (275lb) rider weight limit

detail photos of the specialized aethos s works road bike

They say it’s incredibly robust, with virtually the same tube wall thicknesses as their SL6, and capable of handling gravel roads. (Note: It’s not a gravel bike)

Which is crazy, and it comes almost exclusively from the tube shapes. Almost. Small tweaks add up, and one particularly clever touch is their fork dropout design:

cutaway diagram of specialized aethos fork leg design features

They say most forks end up with a very solid dropout area on the disc side because of the location of the metal flat mount insert, which sits lower to accommodate a 140mm rotor and requires a spacer to go to 160mm.

But, since most every road bike, including this one, is spec’d with 160mm rotors, they designed a slimmer, lighter brake mount and simply molded it into position for 160mm rotors. The result was more hollow area, which removed about 10g of useless material from the dropout. As a bonus, they also saved 2g from the shorter brake mount.

But is the Aethos stiff enough?

frame stiffness to weight comparison chart for new specialized aethos road bike versus the competition

The stiffness-to-weight measurements come in better than it’s key competitors, too. So, despite the incredibly light weight, it descends as well as it can climb. Their team says it gave them a ton of confidence on long, fast mountainous descents. So much so that most of them set new PR’s on their descents on this bike.

If it’s so good, why didn’t they race it in the Tour de France this year? While the frame gets its UCI approved sticker, Specialized says they would have had to add so much weight to hit the UCI minimum, they decided to keep the aero advantages of the Tarmac SL7 since it can be built down to the minimum weight requirement.

Specialized Aethos Founder’s Edition

specialized s-works aethos founders edition

If you’re going to make a frame this light, you may as well do a special build, right?

The lightest model is the Founder’s Edition and comes spec’d with the Roval Alpinist CLX wheels and one-piece bar/stem, Romin S-Works saddle, Shimano Dura-Ace group with power meter, and  CeramicSpeed bottom bracket and derailleur pulleys. Complete bike weight is 5.9kg, which is 100g lighter than the next lightest S-Works build.

specialized s-works aethos founders edition specialized s-works aethos founders edition

Retail price is $14,500, and only 300 will be made. It gets a special Satin Brushed Liquid Silver Holographic paint scheme, with matching details on parts of some components.

2021 Specialized Aethos models, pricing & colors

paint color options for the Specialized Aethos S-Works road bikes and framesets

The Aethos will be offered only at an S-Works level at launch, available in seven different colors, each running $5,200 with all the bits shown on them. Colors include:

  • Gloss Snake Eye Chameleon/Monocoat Black
  • Gloss Forest Green/Gold Pearl/Flake Silver
  • Satin Carbon/Gloss Black Chrome
  • Gloss Clay/Flake Silver
  • Satin Flake Silver/Red Gold Chameleon Tint/Brushed Chrome
  • Satin Carbon/Red Gold Chameleon/Bronze Foil

Click to enlarge any image for more detail. All of which are gorgeous, but there’s one that’s particularly interesting:

specialized aethos s-works jet fuel colorway in unpainted carbon fiber

The Jet Fuel colorway is paint-ready and uses topically applied decals. Meaning, you can remove them easily, whether for aesthetics or because you want to paint it. No other prep is required, though we do wonder why anyone would want to add 100 or so grams of paint to a bike this light.

Aethos S-Works complete bikes

specialized aethos s-works road bike closeup on paint scheme at head tub e
The unique look to the paint isn’t actually hand painted, just a fancy new process they figured out, which looks amazingly like it’s been wiped on by artists.

Complete bikes will come in only two builds, one with Shimano Dura-Ace Di2, shown above, and one with SRAM Red AXS eTap. Both retail for $12,500, and both are electronic only…there are no cable ports for mechanical drivetrains (same for the framesets).

specialized aethos s-works road bike closeup on paint scheme at head tub e

Shared specs on both bikes are:

  • Roval Alpinist carbon seatpost
  • S-Works Short-and-Shallow carbon handlebar
  • S-Works SL alloy stem
  • Roval Alpinist CLX wheels
  • S-Works Turbo Cotton 320tpi 700×26 tires
  • Supacaz Super Sticky Kush bar tape

specialized s works aethos with shimano di2 dura ace

The Shimano build gets full R9100/9150/9170 parts including a dual-sided power meter with 52/36 gearing.

specialized s works aethos with shimano sram red axs etap wireless shifting

The SRAM Red build gets their Quarq powermeter crankset with 48/35 gearing up front.

Aethos geometry chart

specialized aethos geometry chart

Bikes and framesets are available for purchase online and through dealers now.


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