Specialized S-Works Tarmac SL8 Dura-Ace Di2 review

The Specialized S-Works Tarmac SL8 is one of the finest all-round race bikes money can buy today.

It feels aero-bike fast, while blending very low weight, high stiffness and excellent compliance into one easy-to-ride package.

It’s expensive, of course, and there’s perhaps little to warrant an upgrade if you already own a Tarmac SL7, even if it is a slightly better all-rounder.

However, the S-Works Tarmac SL8 blends prodigious performance qualities across the board – I believe it’s the best race bike Specialized has ever made.

Specialized S-Works Tarmac SL8 frameset

When I first got my hands on the Specialized S-Works Tarmac SL8 at the 2023 World Championships in Glasgow, the shape came as little surprise, given it had been leaked in the weeks prior to the event.

Most fingers pointed to the elongated head tube, which Specialized euphemistically dubs the ‘Speed Sniffer’. This is said to capture laminar (clean) airflow at the front of the bike sooner than the Tarmac SL7 for an aerodynamic gain.

On this S-Works bike, the latest Roval Rapide integrated cockpit lives atop this, conferring a four-watt claimed improvement in efficiency, at 45kph.

Meanwhile, the seat tube was narrowed to the same width as the SL7’s seatpost, accommodating a new narrower seatpost, and the fork’s leading edges also saw a slight reshaping.

In pure aerodynamic terms, these key changes are said to make the Tarmac SL8 frameset “16.6 seconds faster over 40km” compared to the Tarmac SL7.

Of course, it’s worth noting the Roval Rapide cockpit can be retro-fitted to the Tarmac SL7 frameset, which would close the aero gap somewhat and cut around 50g of weight from the older bike too.

That said, the biggest changes to the SL8 are arguably to be found elsewhere, with Aethos-inspired rounder shaping applied to the down tube, seatstays and backside of the seat tube and seatpost.

Here, Specialized is reasoning that real-world speed isn’t derived from aerodynamic performance alone.

It says that the rounder shapes bear loads more efficiently, firstly enabling its designers to cut unnecessary carbon (and therefore weight) from the frame.

The rounded shapes are also said to improve through-the-saddle compliance compared to the Tarmac SL7 by six per cent, yet the bottom bracket, head tube and fork have been stiffened.

Specialized doesn’t say by how much in isolation, but it does explain that for the priciest 12r Fact carbon frame, which now weighs a claimed 685g in a size 56cm (compared to an equivalent Tarmac SL7 at 800g), it yields a 33 per cent improvement in stiffness-to-weight ratio.

For the weight weenies out there, a size-medium Canyon Ultimate CFR frame is claimed to weigh 762g, and a medium Ridley Falcn RS frame 825g (it’s worth bearing in mind that both bikes size up a little compared to most brands).

This makes the S-Works Tarmac SL8 one of the lightest frames around right now, ignoring bikes with far less obvious aero treatments.

Regarding more technical details, the fork has a standard 1-1/8in steerer tube, which allows you to use a third-party cockpit or a two-piece Specialized setup, should the integrated setup not be to your taste.

That said, in theory there’s lots of choice should you need to switch the Roval Rapide cockpit for fit reasons, given it can be had in 15 sizes across 38-44cm widths (centre-to-centre) and 75-135mm stem lengths.

The 15mm-offset seatpost is proprietary (a zero-offset post is also available), as is now standard for bikes such as this, but the threaded BSA bottom bracket remains unchanged compared to the Tarmac SL7.

Specialized S-Works Tarmac SL8 Dura-Ace Di2 geometry

Geometry-wise, the Specialized S-Works Tarmac SL8 is set up for rapid handling and an aggressive riding position.

To those already initiated with the Tarmac SL7’s geometry, things will look remarkably similar here.

This is because Specialized went out of its way to change as little as possible, due to feedback from sponsored professional riders such as Remco Evenepoel, Demi Vollering and Kasper Asgreen.

Specialized claims the forward-extended Speed Sniffer head tube design (as opposed to a more common rearward gap-filled approach) enables the steerer tube to remain in the same location relative to the SL7.

Tyre clearance stays at 32mm (measured), so there’s been no need to fiddle with the wheelbase length.

There are race bikes with slightly wider clearances – the Cervélo S5 has clearance for 34mm-wide tyres, for example – but 32mm is likely to satiate the needs of practically any Tarmac customer.

The only notable change is an increase in frameset stack height by 10mm, although once the updated cockpit and headset spacers are taken into account, the figures essentially match the SL7 again.

All of this is to say, the S-Works Tarmac SL8 has all the important dimensions befitting a race bike – matching 73.5-degree head and seat tube angles on my size-56cm test bike – with 410mm chainstays across the size range to balance the rear-end sharpness.

Specialized S-Works Tarmac SL8 Dura-Ace Di2 build

Unsurprisingly, Specialized dresses the S-Works frameset with top-of-the-range, race-ready components.

This Shimano Dura-Ace Di2 R9200 build is pro-level – very similar to the builds Evenepoel and Asgreen have raced for the Soudal Quick-Step team in the latter part of 2023.

With amateur riders in mind, though, there’s a more sensible 52/36t crankset here, paired with a 4iiii dual-sided power meter.

Concerns about value aside, the groupset is the best of the best right now.

Fans of SRAM can also opt for an identically priced Red eTap AXS version, with the same build as described below, apart from a SRAM Red AXS power meter in place of the 4iiii one.

Like the cockpit, the wheelset comes from in-house brand Roval, in the form of its top-spec Rapide CLX II model. These feature a 51mm-deep, 35mm-wide (external) front rim, and a 60mm-deep, 30.5mm-wide rear rim. Both wheels have a contemporary 21mm internal width.

I’ve tested the £1,000-cheaper Roval Rapide CL II wheelset, with identical rims, and came away incredibly impressed with that wheelset’s performance.

My only ‘criticism’ is that I’m not confident this top-spec wheelset truly offers £1,000 more performance, despite having premium DT Swiss 180 EXP hub internals inside a custom Roval ‘Aeroflange’ hub shell, and DT Swiss SINC ceramic bearings.

A similar argument might be made of opting for the S-Works frame versus the standard one, though it’s also fair to say the combination of marginal gains is what many S-Works Tarmac SL8 purchasers will be after.

The wheels are fitted with S-Works Turbo RapidAir 2BR tubeless-ready tyres, set up with Turbo Ultralight butyl inner tubes (in principle, so the sealant for a tubeless setup doesn’t dry between being installed and the bike being sold, while still catering for those who want to run tubes).

The switch to tubeless is one I’d want to make though – the bike I rode at launch was set up tubeless with the same tyres, and I think the ride quality was marginally, but noticeably, better.

Alternatively, you could swap the butyl tubes for latex or TPU ones for a similar gain in performance, though you naturally wouldn’t get the added puncture protection of tubeless sealant this way.

In any case, the tyres themselves are good, offering satisfactory grip and confidence at this level.

I suspect (like many others who are exacting about their bike’s spec) it wouldn’t be long before I swapped to my favourite fast tubeless tyre setup (the Continental Grand Prix 5000 S TR), though, simply for the faith and confidence I have in it.

Moreover, I found the 700x26c dimensions slightly limiting. Specialized road product manager Miles Hubbard said this choice was made in response to market demand, but I think upping the volume to 700x28c rubber would make for a small improvement in overall ride quality with negligible downsides.

I asked Specialized whether it would honour any point-of-purchase spec requests, such as swapping to a different-sized or two-piece cockpit, saddle change or tubeless setup.

It stopped short of confirming it as a policy, preferring instead to leave it up to individual dealers to make the decision (while intimating to me that it encourages a degree of flexibility, subject to stock).

Though it’s fair to say it isn’t the only brand that operates in this way, it’s a shame that Specialized isn’t firm on offering similar-value component swap-outs.

After all, if you’re about to drop £12,000 / $14,000 / €14,000 / AU$19,900 on a bike, it’s not unreasonable to expect it to come set up the way you want it.

As it is, the S-Works Tarmac SL8 comes with a Body Geometry S-Works Power saddle, with carbon fibre rails and underbody – a standard construction, as opposed to the latest 3D-printed ‘Mirror’ saddles.

Value is relative at this rarified level – a similarly equipped Cannondale SuperSix Evo Lab71 costs £12,500 / $15,000 / €14,999 / AU$19,999, for example, while a Trek Madone SLR 9 costs £13,625 / $12,750 / €14,699 / AU$17,999 at the time of writing.

A similarly-equipped Canyon Ultimate CFR Di2 Aero costs £9,499 / €9,999, but of course you can’t get one of these from a local dealer and Canyon is much clearer that no component swaps are offered at the point of purchase.

However, arguably the biggest threat to the S-Works Tarmac SL8, for those trying to look after the purse strings (a little), could be the £8,000 / $8,500 / €8,500 / AU$11,900 Tarmac SL8 Pro.

You get a frame that’s only 95g heavier (in a size 56cm) and a build that appears to give up precious little to the one tested here, for a saving of £4,000 / $5,500 / €5,500 / AU$8,000.

All in, my size 56cm Specialized S-Works Tarmac SL8 Dura-Ace Di2 tipped the scales at 6.76kg, without pedals.

Ready to ride, that’s going to tip just over the UCI’s minimum bike weight limit of 6.8kg, but that’s nevertheless impressive for a bike with this much focus on aerodynamic efficiency.

Specialized S-Works Tarmac SL8 Dura-Ace Di2 ride impressions

The Specialized S-Works Tarmac SL8, in this Dura-Ace Di2 trim, is a delight to ride.

Where Matthew Loveridge, formerly of the BikeRadar parish, felt the S-Works Tarmac SL7 was “single-minded” in its approach to speed, the S-Works Tarmac SL8 is more rounded.

It’s devastatingly quick when you put the effort in, while the near-identical geometry affirms the handling is sharp and direct (yet avoids ever becoming nervous).

However, I was struck by how easy the S-Works Tarmac SL8 was to ride at steady-tempo speeds of around 30-35kph.

It feels efficient yet unperturbed by swirling winds, but is also very comfortable to ride – far more forgiving than a given dedicated aero road bike, for example, yet not tangibly slower (at least, from what I can gather from my own riding).

The ENVE Melee – which earned our 2023 Performance Bike of the Year award – is the only race-oriented bike I’ve ridden that outstrips the S-Works Tarmac SL8 for comfort.

That said, it’s worth noting the Melee came fitted with 700x29c tyres (compared to the Specialized’s 700x26c rubber) on rims with an identical internal width (21mm).

I’ve already mentioned the S-Works Tarmac SL8 would broadly benefit from fitting wider tyres, while it would also be my personal preference to set them up tubeless.

However, aside from the £12,000 price tag, these are about the only notable criticisms I can level at the S-Works Tarmac SL8.

The handling gave me confidence to push hard on descents, and the bike is a fantastic climber, whether you’re taking on longer climbs seated, or punching over steep rises out of the saddle.

The Roval cockpit seems developed with aero performance primarily in mind. I accept this – it’s probably what most S-Works Tarmac SL8 riders will want – but I found the tops a little too thinly bladed to wrap my fingers around comfortably for long periods.

The forward-sweeping top design is also a factor here, effectively causing a disproportionate amount of pressure to be applied to the outer portion of my palms (specifically, the hypothenar) and through my wrists compared to flatter or more ovalised bars.

This is a trade-off with practically all aerodynamic handlebars, though it’s here I hope Specialized’s well-meaning intentions around point-of-purchase component swaps will translate into action, where customers need it.

Specialized S-Works Tarmac SL8 Dura-Ace Di2 bottom line

The Specialized S-Works Tarmac SL8 Dura-Ace Di2 is a no-expense-spared race bike. For some, it will be ‘too much bike’ to extract the most out of it, while the cost will be prohibitive for many.

Those who already own an S-Works Tarmac SL7 can rest easy knowing their bike is still competitive. The S-Works Tarmac SL8 might be excellent, but in pure performance terms, it doesn’t move the goalposts enough to warrant upgrading.

Plus, if this is what Specialized can now achieve with an all-round race bike, and the S-Works Aethos is its finest expression when aero isn’t a priority, I now count myself among those who wonder what it could create if it were to make a truly specialist aero racer.

Coming from a clean slate, though, for those who want a race bike that could legitimately lay claim to being ‘the best of the best’ – cost be damned – I can think of few road bikes that might ride faster on a tarmacked course without punishing you for the privilege.