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Specialized Aethos Pro Ultegra Di2



What a bike. If you have the cash and don't care about aero, buy it
Incredible ride
Low weight
Excellent stiffness
Perfect handling
Gets most of the tech from the S-Works
No power meter
6,660g Recommends

This product has been selected to feature in recommends. That means it's not just scored well, but we think it stands out as special. Go to recommends

At every product is thoroughly tested for as long as it takes to get a proper insight into how well it works. Our reviewers are experienced cyclists that we trust to be objective. While we strive to ensure that opinions expressed are backed up by facts, reviews are by their nature an informed opinion, not a definitive verdict. We don't intentionally try to break anything (except locks) but we do try to look for weak points in any design. The overall score is not just an average of the other scores: it reflects both a product's function and value – with value determined by how a product compares with items of similar spec, quality, and price.

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The Specialized Aethos Pro is an exceptional bike. The ride is truly stunning, with acceleration I've never felt before and handling that's just spot on. It's disappointing to find no power meter and the price is very high compared to rivals, but make no mistake, this is the gold standard for general road bikes. And despite what Specialized says, it's a race bike if you want it to be – just add deeper wheels.

When I first rode the Aethos, I was in the rather flat lands of Solihull. There were no properly steep climbs to really take its measure, but we have plenty of those around the Mendips and Bath – where the Aethos has stunned me. The acceleration is seemingly endless, and things just get better as the gradient increases.

> Buy now: Specialized Aethos Pro Ultegra Di2 from Sigma Sports for £7250.00

I love the handling too, which is sharp and fun. There is a nice float to this bike, with just enough feedback from the road without the harshness that can tire you out over time.

Don't tune out thinking I'm about to drool over this bike for 2,000 words, though – there are good reasons why I'm not. But I want to be quite clear that this is a very special bike. Its lightness is felt with every turn of the pedals, and I'd say this is the gold standard of superbikes right now. Well, for non-racers, anyway.

2021 Specialized Aethos Pro Ultegra Di2.jpg

If you want to believe the marketing, Specialized never set out to make the Aethos so light. Yeah, sure... but whatever the truth, the weight, even on this 'lesser' Pro model, is very impressive. At 6.66kg out of the box (no pedals), it only loses a few hundred grams to the (even more) super expensive versions.

The low weight is instantly noticeable, and I spent my time on the Aethos loving the way it floats up any sort of incline. It just feels like it's constantly surging ahead, and it's truly addictive.

2021 Specialized Aethos Pro Ultegra Di2 - riding 4.jpg

I do realise that hills will always hurt when you decide to go hard up them, but the Aethos is noticeably snappier than the other superbikes I've tested this year.

What goes up must come down, and for me, Specialized has nailed the handling. The tight wheelbase ensures the bike is very nimble, and it's a brilliant bike for coming back down those steep and twisty hills but – while I found the Aethos an absolute blast when pushing the pace in corners – it could be a little too twitchy for some.

2021 Specialized Aethos Pro Ultegra Di2 - head tube badge.jpg

Get the bike up to a cruising speed on the flats and it's a little harder to hold speed than with an aero bike. This year I've been riding the S-Works Venge and the Merida Reacto, and both are faster and arguably better options for rolling terrain.

But both those rivals have deep tube shapes and roll on deep-section wheelsets. The Aethos has round tubes and shallow wheels. Yes, there's a difference in speed on the flats, but it isn't astronomical and I haven't felt held back when I returned to riding with fitter mates.

2021 Specialized Aethos Pro Ultegra Di2 - frame detail.jpg

Given that the majority of aero drag is caused by the rider, getting yourself aero is always going to do more than the frame anyway. With such a short head tube, I found it easy to adopt my usual position and hunkering down low is no problem.

Frame and Fork

So, whoever thought you could reinvent the round tube? If you didn't already know, the Aethos' tube shapes aren't strictly round. There's a little ovalisation to this Fact 10r carbon frame, and according to Specialized, that makes it stiffer where it's needed, more robust and yet lower in weight. All in a tube shape that makes the Aethos look like the old Tarmac SL4.

2021 Specialized Aethos Pro Ultegra Di2 - frame size.jpg

Thankfully (both for Specialized and the rider), the Aethos frame is on a whole other level when it comes to ride quality. The devil is in the technical detail, with Specialized saying a supercomputer analysed 100,000 frame designs and this is what it spat out. Well, they might have used more PR-friendly language, but that was the gist...

2021 Specialized Aethos Pro Ultegra Di2 - fork.jpg

The frame is primarily optimised for pedalling stress and doesn't give any thought to aerodynamics. Specialized says this approach allows the use of fewer carbon layers around those stress points, hence the impressively low frame weight.

While I'm not about to break out the office Dremel to check, I can say the numbers on the scales – combined with the way the Aethos rides – suggest Specialized has achieved its goals.

2021 Specialized Aethos Pro Ultegra Di2 - cable route.jpg

Specialized has stuck with a bit of exposed brake hose, avoiding the current trend of sending everything through the headset. While it isn't as clean as those new race bikes, it's certainly easier to work on, and I'm not concerned about potential aero sacrifices.

2021 Specialized Aethos Pro Ultegra Di2 - bottom bracket.jpg

Elsewhere you find 12x142mm rear and 12x100mm front axles, a threaded bottom bracket – yay! – and space for 32mm tyres.


Quite a few people say the Aethos wouldn't have looked out of place in a bike shop 10 years ago, and the geometry does give off that vibe. It's rather squat, with the 52cm size getting a short 120mm head tube and a top tube that slopes dramatically down.

2021 Specialized Aethos Pro Ultegra Di2 - bars and lever.jpg

Despite this, the Aethos is near identical to the Tarmac SL7 in terms of fit. The 975mm wheelbase, 72.5° head angle and 477mm front centre are identical. The Aethos differs in being slightly higher at 527mm for stack and a touch shorter at 380mm on reach (the SL7 is 517mm and 382mm). A shopping bike this most certainly is not!

Slam the stem as I did and you've got a race bike that makes many lower backs seize up just by looking at it.

2021 Specialized Aethos Pro Ultegra Di2 - top tube logo.jpg

While I'm not fussed on the sloped design on the Aethos, I understand why it's been used. The amount of exposed seatpost allows more flex under load, and the result is a bike that's composed over rough roads – but a look that won't be to everyone's taste.


Roval launched two new top-end wheelsets this year, both going against their long push to make tubeless technology more common. The Alpinist is the low weight climbing option, and the Aethos Pro gets the lower-end model that's slightly heavier and runs on DT Swiss 350 hubs.

2021 Specialized Aethos Pro Ultegra Di2 - front hub.jpg

The wheels are just what you want for a bike like this. They are light and stiff, so they climb very well. The semi-deep rim height means you won't be pushed around by strong winds, but you still get a small aero advantage on the flats.

2021 Specialized Aethos Pro Ultegra Di2 - tyre and rim.jpg

The clincher design certainly frustrates some. Specialized is one of the big pushers of tubeless technology, so these wheels were seen as a step backwards by many. Personally, I can take or leave tubeless (I test a great number of tyres and wheels, so I'm probably exposed to a lot of combinations that don't work properly).

I find inner tubes far easier, and the fact I'm not winning the local road race or bagging that Strava Kom isn't down to my tubes.

2021 Specialized Aethos Pro Ultegra Di2 - rear dsic brake.jpg

These clincher rims have been set up with 26mm S-Works Turbo tyres front and rear. My testing has taken me through seemingly endless muddy lanes and farmers seem to be cutting each hedge just before I ride through.

Despite the challenging conditions, the tyres have been excellent, providing a sure-footed platform for some fast cornering. I've not had any punctures, though I'm always sure that this is down to luck more than anything. I've settled on 70/75psi front/back as my happy-place pressure.

2021 Specialized Aethos Pro Ultegra Di2 - rim.jpg

For the summer I'd want something with a higher thread count than the 120tpi casing, but the black sidewalls are definitely the correct choice for winter use. The S-Works Cotton tyre is a simple upgrade when the weather eventually gets nice again.


So much has been written about Ultegra Di2. I own this groupset and I've had it on a few test bikes; having also ridden Dura-Ace Di2, I'd say that unless you're building a weight weenie bike, don't bother spending the extra money. Ultegra is brilliant.

2021 Specialized Aethos Pro Ultegra Di2 - rear mech.jpg

In fact, with the expected launch of a new Dura-Ace next year, I'd be looking to snap some of this Ultegra up if it starts to drop in price.

2021 Specialized Aethos Pro Ultegra Di2 - fork detail.jpg

In short, the shifting is perfect and the braking is powerful, with loads of control. Given my questionable fitness due to a lack of racing and less time to ride thanks to work, I've been loving the semi-compact 52/36 chainring combination.

2021 Specialized Aethos Pro Ultegra Di2 - front mech.jpg

When paired with the 11-32T cassette, the easiest climbing gear is absolutely spot on for the steeper hills in Bath, but the 52-11 is big enough for chasing those annoyingly fast friends.

2021 Specialized Aethos Pro Ultegra Di2 - cassette.jpg

One thing that is badly lacking here, and I'd like to remind you of the £7,250 price tag, is a power meter. I could forgive the lack of a dual-sided design, but to get nothing is disappointing.

> Cycling power meters: explore these 24 systems to find the best one for you

Look at the new Giant TCR Advanced Pro 0 at £4,799 and you find a dual-sided power meter, plus the same Di2 groupset you get here.

Finishing Kit

As you'd hope, the finishing kit includes a lot of carbon. The handlebar is the S-Works short and shallow model. It provides a comfortable range of hand positions that are all easily accessible, while also doing a good job of damping out road buzz.

2021 Specialized Aethos Pro Ultegra Di2 - bars 1.jpg

The stem is a simple aluminium design but more interestingly, the seat post is brand new and the same model found on the super-expensive Aethos models.

2021 Specialized Aethos Pro Ultegra Di2 - saddle 2.jpg

The carbon post is 27.2mm in diameter and gives a setback of 20mm. The two-bolt design is dead easy to use and, despite the low weight of the post, I've had no issues with it slipping, even after clouting a fair few potholes.


Okay, allow me to have a bit of a moan. Why, Specialized, when you have two perfectly good road bikes (the Venge and the Tarmac) already, do we need the Tarmac to become a lightweight aero bike and the already aero Venge to be phased out?

> 28 of the best and fastest 2021 aero road bikes — wind-cheating bikes with an extra turn of speed

Why not just make the Venge the bike that combines aero and low weight and take the Tarmac back to its roots of low weight, high stiffness and brilliant handling? Because that's what the Aethos is!

2021 Specialized Aethos Pro Ultegra Di2 - UCI badge.jpg

Specialized insisting the Aethos isn't a race bike, yet getting UCI certification for the frameset, is also odd.

Pro versus S-Works

When the Aethos launched, I rode the SRAM Red eTap AXS S-Works model and personally, I find it hard to point to the £4,750 difference between that £12,000 version and the £7,250 model here.

The Pro is about 660g heavier, of which around 200g is accounted for by the Ultegra Di2 groupset and a bit more from the Roval Alpinist CL wheels rather than the CLX. In fact, the rims are the same, so the weight difference in the wheels is down to slightly cheaper spokes and hubs.

2021 Specialized Aethos Pro Ultegra Di2 - drivetrain.jpg

But the ride quality differences would be splitting hairs, and I'd say Specialized has done a great job delivering the majority of the S-Works tech in the Pro version.


If you're looking to buy the Aethos – good choice. It's an exceptional bike, but you're going to have to dig deep to fund it. The Giant TCR Advanced Pro 0 Disc mentioned earlier has a very similar spec for £4,799, and if you hand over seven grand to other brands, you're likely to get Dura-Ace Di2 or a power meter in return.

Canyon has the Ultimate CF SLX 9 Disc at £7,199, and Trek's Emonda SLR 7 is £6,450. All of these feature some form of aero tubing. Few brands are making high-end bikes that don't pay some attention to aero these days, but if we look at ride quality, climbing ability and handling, the Aethos is a worthy contender indeed.


Yes, I have some grumbles regarding the lack of a power meter and the pricing, but a bloody brilliant bike it is. The way the Aethos constantly wants to bound forward like a dog after a squirrel makes it incredibly fun to ride. The low weight is matched with great stiffness, and the ride remains pretty composed over rough tarmac.

Specialized says the Aethos has handling at the front and centre of its design, and while I was sceptical before riding it, they seem to be telling the truth. It's just a blast to ride.


What a bike. If you have the cash and don't care about aero, buy it

If you're thinking of buying this product using a cashback deal why not use the Top Cashback page and get some top cashback while helping to support your favourite independent cycling website test report

Make and model: Specialized Aethos Pro Ultegra Di2

Size tested: 52

About the bike

List the components used to build up the bike.

FRAME Aethos FACT 10r Carbon, Rider First Engineered, Threaded BB, 12x142mm thru-axle, flat-mount disc

FORK FACT Carbon, 12x100mm thru-axle, flat-mount disc

HANDLEBARS S-Works Short & Shallow

STEM Specialized Pro SL, alloy, 4-bolt

TAPE Supacaz Super Sticky Kush

SADDLE Body Geometry Power Pro, Hollow Titanium Rails, Carbon Fiber Base

SEATPOST Roval Alpinist Carbon Seatpost

SEAT BINDER Specialized Alloy, 30.0mm

FRONT BRAKE Shimano Ultegra R8070, hydraulic disc

REAR BRAKE Shimano Ultegra R8070, hydraulic disc

FRONT DERAILLEUR Shimano Ultegra Di2 R8050, braze-on

REAR DERAILLEUR Shimano Ultegra Di2 R8050, GS medium cage

CRANKSET Shimano Ultegra R8000, HollowTech 2, 11-speed

CHAIN Shimano Ultegra, 11-speed

FRONT WHEEL Roval Alpinist CL, 21mm internal width carbon rim, 33mm depth, Win Tunnel Engineered, DT for Roval 350 hub, DT Swiss Aerolite spokes

REAR WHEEL Roval Alpinist CL, 21mm internal width carbon rim, 33mm depth, Win Tunnel Engineered, DT for Roval 350 hub, DT Swiss Aerolite spokes

FRONT TYRE S-Works Turbo, 120 TPI, folding bead, BlackBelt protection, 700x26mm

REAR TYRE S-Works Turbo, 120 TPI, folding bead, BlackBelt protection, 700x26mm

INNER TUBES Turbo Ultralight, 48mm Presta valve

Tell us what the bike is for and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about the bike?

"The Aethos line promises three things: unprecedented weight savings, perfectly-balanced ride quality, and undeniable style. For the Aethos Pro we threw out the rulebook to create the ride of your life."

Where does this model sit in the range? Tell us briefly about the cheaper options and the more expensive options

It's middling: you can get the S-Works models at around £12,000, or spend less on the Expert at £5,500.

Frame and fork

Overall rating for frame and fork

Tell us about the build quality and finish of the frame and fork?

It is excellent.

Tell us about the materials used in the frame and fork?

It's Fact 10r carbon, so not Specialized's fanciest stuff. The more expensive Aethos models use Specialized's Fact 12r carbon, which is lighter for the same level of stiffness.

Tell us about the geometry of the frame and fork?

It's actually very similar to the SL7, even though it doesn't look it at first glance. This is a performance road bike, no doubt about it.

How was the bike in terms of height and reach? How did it compare to other bikes of the same stated size?

You can get long and low if you want. I'd say it's very similar to the aero race bikes I've been riding this year.

Riding the bike

Was the bike comfortable to ride? Tell us how you felt about the ride quality.

Very comfortable. The stiffness doesn't translate into harshness, meaning you don't get beaten up over a longer ride.

Did the bike feel stiff in the right places? Did any part of the bike feel too stiff or too flexible?

The front end and bottom bracket are entirely stiff enough.

How did the bike transfer power? Did it feel efficient?

Incredibly efficient. It really wants to leap forward.

Was there any toe-clip overlap with the front wheel? If so was it a problem?

A little, but I never find this to be an issue.

How would you describe the steering? Was it lively neutral or unresponsive? Very lively and I loved it.

Tell us some more about the handling. How did the bike feel overall? Did it do particular things well or badly?

Fast, technical corners are great fun on this bike.

Which components had the most effect (good or bad) on the bike's comfort? would you recommend any changes?

The rims are 21mm wide internally. That gives excellent support to the tyres, and you can get a lovely profile on them – ideal for increasing comfort.

Rate the bike for efficiency of power transfer:
Rate the bike for acceleration:
Rate the bike for sprinting:

Not as stable as the Merida Reacto or Specialized Venge.

Rate the bike for high speed stability:
Rate the bike for cruising speed stability:
Rate the bike for low speed stability:
Rate the bike for flat cornering:
Rate the bike for cornering on descents:
Rate the bike for climbing:

The drivetrain

Rate the drivetrain for performance:
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Rate the drivetrain for value:

Tell us some more about the drivetrain. Anything you particularly did or didn't like? Any components which didn't work well together?

No power meter!

Wheels and tyres

Rate the wheels for performance:
Rate the wheels for durability:
Rate the wheels for weight:
Rate the wheels for comfort:
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Tell us some more about the wheels.Did they work well in the conditions you encountered? Would you change the wheels? If so what for?

Maybe throw in a deeper set of wheels if you want to go racing. Otherwise, they're great.

Rate the tyres for performance:
Rate the tyres for durability:
Rate the tyres for weight:
Rate the tyres for comfort:
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Tell us some more about the tyres. Did they work well in the conditions you encountered? Would you change the tyres? If so what for?

Handle wet, debris-strewn roads easily.


Rate the controls for performance:
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Your summary

Did you enjoy riding the bike? Yes

Would you consider buying the bike? Yes – as soon as I stop racing, I want one

Would you recommend the bike to a friend? Yes

How does the price compare to that of similar bikes in the market, including ones recently tested on

It is high. For the spec, it's higher than pretty much everything we've tested.

Rate the bike overall for performance:
Rate the bike overall for value:

Use this box to explain your overall score

The Aethos has some minor negatives, like the lack of a power meter at this price, but that doesn't detract from what is an exceptional bike for the simple joy of riding.

The handling is spot on, the way it climbs is dreamy and for the non-racer (and most recreational racers) this is the gold standard of superbikes.

Overall rating: 9/10

About the tester

Age: 24  Height: 177cm  Weight: 62kg

I usually ride: Cannondale Supersix Di2  My best bike is:

I've been riding for: 5-10 years  I ride: Most days  I would class myself as: Expert

I regularly do the following types of riding: road racing, time trialling, cyclo cross, commuting, club rides, general fitness riding, I specialise in the Cafe Ride!

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