“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.



  1. Klaster_1 on

    The frameset should be easy to build into sub-5kg road disc bike, with reasonable components. I wish I had enough disposable income to spend on something like it. 5.9kg is overweight.

  2. Chris on

    Can you imagine if they made a rim brake version? That would be a super light build! Nice work. It will be interesting to hear how it rides compared to the SL7.

  3. Pete on

    So they simplified the frame (finally!), and made it look real perdy. That’s great!

    But $5200 plus tax for frame+fork only?
    And $14K for a bike?

    gddam this industry.

  4. pm732 on

    “But is the Aethos stiff enough?”

    you ask the question but then dont answer it lol. RATIO is not the same as absolute stiffness. how does the ACTUAL stiffness compare.

    more marketing….

    • Mo on

      It wouldn’t be particularly as useful to know the “stiffness” as you suggest it would. The test measurements, and what the bar graph refers to, are a specific test used by TOUR magazine — the Zedler stiffness-to-weight protocol —  and reflect a score given based on how a specific frame handles the test(s) developed to measure a frame’s stiffness. If you want the “stiffness score” they arrive at, they are most likely as follows: Specialized Aethos – 95256; Canyon Ultimate CF Evo – 97528; Cervélo RCA – 94470; Trek Émonda SLR 9 – 95172; Specialized S-Works Tarmac SL4 – 103350; Giant TCR Advanced SL – 103071; Scott Addict RC Ultimate- 106750; Lightweight Urgestalt Disc – 104190. If you’ll notice, only the Cervélo RCA and Trek Émonda are “less stiff” in the absolute terms defined by the testing protocol. What that means is, given their weight, they aren’t as efficient as the Aethos in applying material to increase stiffness. (This assumes that stiffness is their goal, which it may or may not be). 

      A better way to read the graph, and what I assume the author is intending to do, is to see that the bike is sufficiently stiff given its weight, as well as stiffer in the absolute terms of the test as two other bikes — the Cervelo and Trek — that to my knowledge aren’t particularly “noodly.”

  5. Ilja on

    I wonder why they didn’t keep the Venge brand alive (their Tarmac SL7 looks like Venge), and made this the new Tarmac? New name might make it easier to start at a higher price level?

  6. FritzP on

    @pm732: but can we figure out relative stiffness (s) to compare the two? The chart in the above article provides weight (w) and stiffness to weight (sw) ratio. Would the equation be s/w=sw solving for stiffness: s = w*sw? Taking the numbers from the chart gives an Aethos stiffness of 95,256. Similarly SL6 stiffness is 104,940 (units?). So the SL6 is approx 9.2% stiffer. Which stiffness tho… at the BB, at the HT?

    So much for not being race geo: Aethos geo is nearly identical to the original SL6, the only difference i can see is the Aethos chainstays are 5mm longer. https://www.specialized.com/us/en/s-works-tarmac-sl6-frameset/p/154660?color=&searchText=70619-0544

    The SL7 has a few mm more reach and 1cm less stack, so longer and lower than the SL6/Aethos.

    My 56cm rim brake SL6 Pro with CLX50 wheels & red 22 is 14.2 lbs including pedals, cages, computer mount and sensor.

  7. Erich on

    Feels like a missed opportunity to add a few grams in routing for mechanical systems and go after Trek for the aspirational lightweight road bike market. Maybe that’ll be in the future if this project pays for itself. At $5200 for an overseas frame, even with fancy paint, they should still be clearing good margin to pay down the R+D and mold costs pretty quickly.

    • Dan Lind on

      @Erich I’m guessing because mechanical systems are not the future…wireless is. Electronic is here for the time being, but we know Shimano is working on a wireless system also, so it’s only a matter of time.

      No need to create a separate mold for a few holes in the frame if you don’t need to. This is not really a bike for the non-racing masses, it’s a bike for the non-racing people with too much money who want to brag about having the lightest production bike available crowd who have $12k to spend on a fancy toy. They don’t want extra cables cluttering things up either. 😉

  8. Wickedstealthy on

    So not for racing but using a geometry which is hard for most without reverting to 2cm+ spacer towers. Strange thinking

  9. None Given on

    has anyone logged into WeightWeenies to see if they are collectively okay? This has got to be a huge day for them…

    • Shafty on

      Yawn. This is the same tired cliche of chasing weight numbers. I’m bored of it. They say their goal was *totally unrelated* to racing, and also *super relevant* to “regular riders”. (deleted), you know that’s total BS. With those MSRPs those bikes will be relevant to hardly anyone. You don’t make the “world’s lightest disc brake road bike” accidentally, that was their goal, make no mistake. It’s just slick marketing word salad.

  10. Jim Rawson on

    How do they test stiffness.. torsional, or BB only. Do they test with the fork, or just the frame with no fork. Do tell

  11. Dylan Sutton on

    “What if we built a bike that’s simply for the love of riding?”
    “Nah, let’s build one for spec sheet bragging rights, that’s much easier for marketing.”

  12. Czechmate on

    Here is a message to all those demanding a rim brake version of this bike : rim brakes are still too ubiquitous and too visible in the pro peloton to be widely accepted as sub-performing or better still, obsolete.
    Today, Specialized can’t hope to cash in on this obsolescence like it does here with a “standard” round seatpost, a “standard” tapered headset, a threaded bottom bracket and exposed cables… a brilliantly clever move by their marketing department, by the way, I must admit. Because I mean, really, who would be bold enough to use the concept of “standard” or “sub-performing” as a marketing ploy ?
    Making an educated guess, I’d say the rim brake version of this bike is on hold for two years or so until rim brakes disappear entirely from the pro peloton.
    Then and only then, will the market be ripe for a release of the rim brake Aethos.
    “We’ve broken the rules of designing bikes by redesigning the bike that broke the rules of designing bikes. Yesterday, orange was the new black. Today, jet fuel is the new orange. The rim brake Aethos, made especially for you, the regular Joe. Oh, and it’s lighter than ever before.”
    Nobody will notice the “standard” thousand-dollar price hike on the little “standard” price tag hiding in plain sight amongst all that jet fuel of an advertising slogan.

  13. Eggs Benedict on

    What would you change in the geometry? I think the only thing I would change would be to add 2cm to the stack height for my frame size.

  14. Eggs Benedict on

    This was supposed to be reply to someone’s comment above (Bob). But for what ever reason it got placed at the bottom of the list.

  15. Yurp on

    “What if we built a bike that’s simply for the love of riding?”
    If you did it shouldn’t cost anything near even the frameset SRP here, for starters.

  16. Sajuuk on

    Not really seeing the value of this compared to something like a BH Ultralight EVO Disc. This seems to be for the mountain jockey weight weenie crowd. I’d be afraid of this thing exploding under any bigger person putting out over 1000 watts.

  17. Brian on

    So subtract the cost of the frame (plus or minus the special paint), and the build kit for the $14,200 Founder’s Edition costs $9,300. My goodness.

  18. miclaroc on

    Had the chance to see a few of these in-person today, must say they are extremely “generic” looking – “carbon bike” . Side-by-side with an Sl7 there was not much sex-appeal or second-thought as to which Id rather have. All worthy else aside, I believe aesthetic excitement is a necessary component in a $12k bike alongside ride quality, weight, build quality etc. This did not “arouse”
    However I DO LAUD the effort, it feels Specialized have read every single complaint Ive posted on board like this over the past 2 years and made this just for me(almost) so CHEERS to their effort. Just add a bit more vavvoom and youve got as formidable bike there!! They were quite light, my inner wweenie was pleased.
    PS the *Limited Edition Silver bike was NOT brushed as it is on the website, its just painted silver.

  19. Robin on

    Nothing? What does that mean? Are you suggesting they didn’t actually perform tests to measure any particular stiffness? That’s a bold position to make up.

  20. Mecanico do Paladar on

    The authentic weight wennie does not need this frame to achieve a total bike weight of 5900g.
    He goes for his grand father rusty stell frame and builds a sub 5kg bike when the devil blinks an eye.
    Going back to bed again.

  21. None Given on

    I would not at all say “not for racing” – it is simply “Not for UCI” racing. That is what, .001% of the population of their assumed market? (US). So, someone wants to enter a Cat3-4-5 Crit, no one will say boo if they are on that bike. Doubtful if someone who is 1 would have any complaints (but in reality, would not in general have the funds for the bike).

  22. Tony P. on

    Jeez, this is gonna break. Better start practicing your JRA speech to specialized now, cuz it’s gonna be a buncha broken carbon

  23. Paul on

    I agree. This would be a perfect opportunity to reintroduce rim brakes back into the equation. Bike manufacturers have been brainwashing and coercing the bike buying public into thinking they want or need disc brakes and unnecessary aero features. Whilst doing this they have delivered excessively heavy bikes with unsightly cable management. My main concern is that this bike is not stiff enough for most riders. The original Tarmac was a bit of a disaster in that department but it was light. As others have pointed out, stiffness to weight is not overall stiffness.

  24. Shashin on

    As noted before, it’s the frame that’s 585 grams, not the bike and on that basis the heading is wrong. Is the problem that you don’t understand metric units?

  25. Veselin Mandaric on

    Epoxy based composites MUST be painted.
    Aerospace encapsulate the whole part. Outside + Inside.
    Epoxy is moisture absorbent. Moisture get in between plies of carbon, expand and evaporate. Cause separation and cracks.
    Thermoplastics don’t have to be protected. I guess frame will never be made out of them, process of curing/heating is “horrible”.


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