Specialized Aethos Pro Ultegra Di2

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.

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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.

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.

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.

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.

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.

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...

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.

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.

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

Geometry

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.

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.

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.

Wheels

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.

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.

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.

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.

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.

Groupset

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.

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.

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.

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.

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.

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.

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.

Gripes

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!

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.

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.

Value

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.

Overall

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.

Verdict

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