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Specialized releases Aethos: "the lightest disc brake road bike ever"

New model is built around a 588g frame with complete bikes from 5.9kg – but it’s all about the ride quality, says Specialized

Specialized has revealed a new disc brake road bike called the S-Works Aethos which it says is the most technologically advanced model it has made, built around a frame that weighs just 588g (56cm version). The US brand says that it chased ride quality rather than weight in itself, but that its 5.9kg complete bikes are the lightest disc brake models ever produced with everyday – albeit high-end – components.

Although the Aethos frame is UCI-approved, it isn’t designed for racing, being well under the 6.8kg minimum weight limit. So what’s the point of the Aethos? Specialized says that it is aimed at riders who prioritise handling and ride quality above aerodynamics, and who want the ultimate high-performance road bike unrestricted by competition rules.

2021 Specialized Aethos down tube - 1.jpeg

“There are riders out there that yearn for more than racing, that see the experiences of the open road as an equivalent to toeing a start line,” says Specialized.

“The demands of this sophisticated rider equal that of any racer, for where racers want for speed, these riders demand a package that accounts for everything else, too. Sprightly climbs towards the clouds, wicked descents on the other side – they demand superior handling and an unrivalled ride from a bike that’s the epitome of quality, performance, and style.”

Oh, and if that appeals, you’d better have a few quid in your pocket too because the Aethos ain't cheap... But you already guessed that.

The design process

The Aethos is the culmination of a project by Peter Denk and Sebastian Sevet, the engineers who worked on the Specialized Tarmac SL6 (and many, many other projects; Peter Denk has notably developed bikes for Cannondale and Scott in the past).

“The prototypes of the SL6 were on the testing machines, and we just love watching frames on the testing machines; there’s so much you can learn from it,” says Peter. “I was staring at the machine for 45 minutes and tried to see how the forces flow through the frame – the pedalling forces and cornering forces.

2021 Specialized Aethos action  - 4.jpeg

"There’s a dogma in cycling that we need a big down tube, a fat bottom bracket and great chainstays, but when I saw how these frames behaved I thought that maybe we’re wrong, maybe something completely different is going on and we’re using the wrong proportions, the wrong shapes and the wrong tapering.

“I went home from Morgan Hill [California, where Specialized is based] to Germany and discussed it with Sebastian. We thought there was a smarter way to do things.”

Peter and Sebastian felt that the bike industry’s understanding of how forces flow through a frame was incomplete and that there was potential for massive improvements. They thought they could improve on the ride experience delivered by a 700g frame, believing they could go significantly lighter, but required what Specialized describes as “staggeringly large supercomputer simulations” to work out the the optimum tube shapes.

“We used [these supercomputer simulations] to subtly alter round tube shapes,” says Specialized. “This made them more conical in key areas to deliver huge gains in stiffness and balance with the minimum amount of material.”

Peter and Sebastian decided that there must be no ‘lazy fibres’ in the finished design. In other words, every fibre should be loaded and tense – doing a job – rather than just adding weight. They concluded that there were too many ‘stiffness layers’ – or extra plies – in most frames.

“With these new tube shapes, we needed an entirely new way to lay-up frames,” says Specialized. “Thankfully, it’s one which resulted in reducing the number of needed plies by 11% compared to the Tarmac S-Works SL6.

“By utilising larger, longer, and more continuous, unbroken plies, we were able to achieve more consistent positioning than on any frame we’ve made before.

2021 Specialized Aethos action  - 1.jpeg

“The wall thicknesses of the tubes themselves are substantial throughout the frame, but because of the smaller number of the stiffness layers, the overall weight went down significantly.”

Peter says he knew that they were on to something when their first prototype frame was very stiff in most areas, passed about 70% of Specialized’s internal tests (which is high for a design at this stage of its development) and weighed just 554g.

“We put it on the test machine and the frame behaved so beautifully – it was so stable,” says Peter. “We only had to add 10g and we could test ride the frame. That was the moment we knew we had discovered something big.”

Specialized doesn’t publish detailed material specs but the S-Works Aethos is made using what it calls FACT 12r carbon and layup technology. It says that the finished version of the S-Works Aethos frame weighs just 588g in the lightest colourways (that’s the average for a 56cm frame; some individual examples in that size might be as low as 580g) while the fork is 270g. According to Specialized, the Aethos outperforms key rivals like the Canyon Ultimate CF Evo 10.0 Ltd and Cervelo RCA in terms of stiffness to weight – although these claims haven’t been independently verified.

2021 Specialized Aethos action  - 5.jpeg

Specialized also says that the S-Works Aethos is no more delicate than other bikes of its ilk, coming with a rider weight limit of 125kg (19st 10lb). In fact, Specialized describes it as “exceptionally durable” thanks to optimisation of the tube shapes and layup.

“Abuse this frame like any other frame,” says Peter Denk.

Specialized releases a Founder’s Edition of every new platform, in the Aethos’s case limited to 300 complete bikes, each with a claimed weight of just 5.9kg. To get that low the frame is fitted with Roval’s 1,248g Alpinist CLX wheels and the Roval Alpinist bar/stem cockpit (the first production bike to feature these). It has a Shimano Dura-Ace Di2 groupset with a CeramicSpeed bottom bracket and pulley wheels.

Find out about Roval’s Alpinist wheels here.  

Frame details

The S-Works Aethos frame is compatible only with electronic drivetrains and hydraulic disc brakes.

2021 Specialized Aethos fork crown - 1.jpeg

Complete bikes come specced with 700x26mm tyres but you can fit tyres up to 32mm wide on 21mm rims. This leaves 4mm of space all round.

If you want to run a 1x (single chainring) drivetrain, you can remove the front derailleur hanger.

2021 Specialized Aethos BB - 1.jpeg

The Aethos uses a 68mm BSA threaded bottom bracket, like the recently released Tarmac SL7, and takes a 27.2mm diameter seatpost.

Read our review of the Specialized S-Works Tarmac SL7 Dura-Ace Di2 2021

It features 142x12 and 100x12 thru axles and follows Shimano’s flat mount disc brake standard.

2021 Specialized Aethos fork dropout - 1.jpeg

Weights

A 56cm S-Works Aethos has a painted frame weight of 588g in the lightest finish (Satin Carbon/Jetfuel), according to Specialized. Other finishes add 25-45g.

The complete claimed weight of the S-Works Di2 model is 6kg in the Carbon/Chameleon Red Gold colourway.

The weight varies according to frame size, of course. A 49cm frame in a Satin Carbon/Jetfuel colourway is said to average 550g while a 61cm frame averages 643g.

As mentioned above, the Founder's Edition comes in at a claimed 5.9kg.

Geometry

The Aethos has fit/handling geometry that's identical to that of the Tarmac SL7 (the stack and reach are slightly different, but that’s because the SL7 has a cutaway at the top of the head tube and a tall bearing cover).

2021 Specialized Aethos geometry - 1

Models

S-Works Aethos Shimano Dura-Ace Di2 £10,750
Groupset Shimano Dura-Ace Di2
Wheelset Roval Alpinist CLX
Handlebar S-Works Carbon
Seatpost Roval Alpinist
Saddle S-Works Power
Weight 6.0kg

S-Works Aethos SRAM Red eTap AXS £10,750
Groupset SRAM Red eTap AXS
Wheelset Roval Alpinist CLX
Handlebar S-Works Carbon
Seatpost Roval Alpinist
Saddle S-Works Power
Weight 6.26kg

S-Works Aethos Founder's Edition £13,000
Groupset Shimano Dura-Ace Di2
Wheelset Roval Alpinist CLX
Handlebar Roval Alpinist cockpit (one-piece bar/stem)
Seatpost Roval Alpinist
Saddle S-Works Power Arc
Weight 5.9kg

S-Works Aethos frameset £4,000

Get more details from www.specialized.com

Mat has been in cycling media since 1996, on titles including BikeRadar, Total Bike, Total Mountain Bike, What Mountain Bike and Mountain Biking UK, and he has been editor of 220 Triathlon and Cycling Plus. Mat has been road.cc technical editor for over a decade, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. We send him off around the world to get all the news from launches and shows too. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a winner of the Cycling Media Award for Specialist Online Writer. Now over 50, he's riding road and gravel bikes most days for fun and fitness rather than training for competitions.

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23 comments

Avatar
Jimmy Ray Will | 3 years ago
1 like

I was reading some great marketing blurb on this bike somewhere... Specialized saying that bottom bracket stiffness actually isn't important to bike performance.... *turning off marketing speak* I understood this to mean that the bikes probably a bit flexy around the bottom bracket. 

Avatar
Nick T replied to Jimmy Ray Will | 3 years ago
1 like

I wouldn't be surprised if the real reason we won't see professionals racing this is because it's a bit of a noodle, rather than false claims of illegality

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fukawitribe replied to Nick T | 3 years ago
0 likes

It's explicitly not designed for racing, according to their blurb, and that isn't to do with the weight of the frameset per se - so may well be not stiff enough for a professional team. Given that's still not what it's designed for, I doubt Specialized are bothered.

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Nick T replied to fukawitribe | 3 years ago
0 likes

Of course they aren't bothered, just need to convince people it's so advanced it's illegal and it'll still sell

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fukawitribe replied to Nick T | 3 years ago
0 likes

Of course they're trying to sell, that's basically every business - you seem obsessed with one part of their spiel though, and seem to be ignoring what they're actually pushing as the latest, greatest thing (whether that's bollocks or not).

Avatar
Yorky-M | 3 years ago
3 likes

Totally refuse to be drawn in to the big S marketing wank. Resist , you do not need this. Take your family on a holiday and get a handmade LOOK 695 for 4 grand and still have 5 grand left over. People can spend their own money how they want but a price tag does not mean better or even better-for-you. To the customer who need the sub 6kg bike there should be a set of scales showing a bodyfat under 6% and a complete data healthcheck on his/her hard drive to make sure sanity is intact. Want/need/create desire? rational thought? price per mile? lotta shite?

Avatar
Rapha Nadal replied to Yorky-M | 3 years ago
3 likes

mylesrants wrote:

Totally refuse to be drawn in to the big S marketing wank. Resist , you do not need this. Take your family on a holiday and get a handmade LOOK 695 for 4 grand and still have 5 grand left over. People can spend their own money how they want but a price tag does not mean better or even better-for-you. To the customer who need the sub 6kg bike there should be a set of scales showing a bodyfat under 6% and a complete data healthcheck on his/her hard drive to make sure sanity is intact. Want/need/create desire? rational thought? price per mile? lotta shite?

You sound like fun.

Avatar
60kg lean keen ... | 3 years ago
1 like

Just lovey if I had the cash and could justify spending that amount on a bike, I would be in! Yes the old man in Me would like it even purer - mec groupo and rim brakes but that's just being picky, I understand this bike is to be enjoyed not just for show and used for all seasons bar the grisliest of weather, hence the discs and elc gropo. For Me and so many others. riding is about getting outside and enjoying the space and freedom, not strava segments, average speed and data, It's about the feeling not how fast I can go!  Well done Specialized.

 

Avatar
pkaro | 3 years ago
2 likes

Those who want bike companies to abandon UCI set limitations will never be satisfied. Yes it could have rim brakes - but then it would be retreating well-trodden ground.

A 6 kg road bike with disc brakes is fantastic, for the type of riding I do this would be absolutely perfect. Just need to find a spare $10K

Avatar
Jem PT | 3 years ago
1 like

But I thought the wind-tunnel had conclusively told us that aero had more effect upon performance than weight? Or is that what Specialized will say in a few years when they bring out an Aethos Aero?

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Secret_squirrel replied to Jem PT | 3 years ago
0 likes

Of course they will, along with the electrically actuated drum brakes and 650c wheels it comes with.

Marketeers gonna market.

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Kadinkski replied to Jem PT | 3 years ago
0 likes

Jem PT wrote:

But I thought the wind-tunnel had conclusively told us that aero had more effect upon performance than weight? Or is that what Specialized will say in a few years when they bring out an Aethos Aero?

This isn't a performance bike, they're very clear about that. They don't even try and claim it will give better performance than aero. It's not even race legal FFS. Its so weird how people don't seem to understand basic English.

 

Avatar
Nick T replied to Kadinkski | 3 years ago
1 like

It is race legal, it's been approved as such by the UCI. All you have to do is build it to the minimum weight, with added lead ballast if required - like every other lightweight frame in the last 15-20 years

Avatar
Toffee | 3 years ago
2 likes

Classic bike industry move. Release one bike and claim it's possible to now have comfort, low weight and aero in one package, and there's no reason to pick and choose, then release a bike that removes the aero element in the name of ride comfort and low weight.

Avatar
pkaro replied to Toffee | 3 years ago
0 likes

Toffee wrote:

Classic bike industry move. Release one bike and claim it's possible to now have comfort, low weight and aero in one package, and there's no reason to pick and choose, then release a bike that removes the aero element in the name of ride comfort and low weight.

Stop being obtuse, this is a bike that's not designed with the weight limit in mind.

Avatar
SimoninSpalding | 3 years ago
1 like

So it turns out that round tubes give better ride quality and threaded bottom brackets allow low weight frames. Who knew?

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fukawitribe replied to SimoninSpalding | 3 years ago
0 likes

SimoninSpalding wrote:

So it turns out that round tubes give better ride quality ... Who knew?

No-one, because it's not even wrong.

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willsdad | 3 years ago
0 likes

I am don't really like carbon aero frames, but I see why its the perfect material to get the complex shapes. Isn't making round tubes out of carbon totally missing the point? I like round tubes on metal frames (Titanium or steel) but carbon fibre tubes should be in a golf bag.

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Nick T | 3 years ago
0 likes

Bravo Specialized, you've invented the skinny tube frame 👏

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NZ Vegan Rider replied to Nick T | 3 years ago
1 like

It just needs some rim brakes to be really light (and better looking, better imho)  3

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gaz753 replied to NZ Vegan Rider | 3 years ago
1 like

And lugs

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Steve K replied to Nick T | 3 years ago
1 like
Nick T wrote:

Bravo Specialized, you've invented the skinny tube frame 👏

Not sure I'd call those tubes skinny.

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JL77 | 3 years ago
0 likes

Take the Di2 or AXS version, add some light (real) mid-depth aero wheels and perhaps an aero cockpit, and you may have the best off all road worlds. Provided that the stack & reach match. The price not withstanding.

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