Specialized S-Works Tarmac SL8 review: one road bike to rule them all

Some three years since the Tarmac SL7 launched (and twenty years since the very first Tarmac), the much anticipated eighth iteration of the US brand’s race machine finally landed.

With the brand making big claims - including ‘one bike to rule them all’ and ‘the fastest road bike ever’ - its billing is certainly enticing, and it promises to juggle aerodynamics with weight and ride quality to an extent not seen before.

I got my hands on a Specialized S-Works Tarmac SL8 - Shimano Dura-Ace Di2  for a couple of months and clocked up thousands of kilometres of testing in London, the home counties and Girona. Best road bike ever? I think so.

Specialized S-Works Tarmac SL8 review

Specialized S-Works Tarmac SL8 review: price and availability

The Tarmac SL8 was announced and went on sale in early August 2023.

The S-Works SL8 is available with two different groupsets (all other components are the same): the SRAM Red eTap AXS and the Shimano Dura-Ace Di2, and both are priced at £12,000/ $14,000/ €14,000/ AU$ 19,900. Incidentally, this is £1,000 less than the list price of the SL7 used to be. 

Each of the two models comes in two colourways, both offering the Satin Fog Tint / Green Ghost Pearl / Red Ghost Pearl Fade - this is the pearly white version I rode. 

The Di2 model’s second colour is Satin Carbon / Viavi Cynan Blue / Viavi Silver-Blue Pearl Fade / Gloss Metallic White Silver - put simply, black satin finish with S-Works decals in a metallic silver colour which gives a nice pop.  

The SRAM version’s second colour is Gloss Red Sky / Fiery Red Strata / Satin White, which overall is gloss red with swirls within the finish which looks cool. 

The Tarmac SL8 also comes in three other spec models, namely the Pro at £8,000, Expert at £6,000 and Comp at £4,500.

Specialized S-Works Tarmac SL8 review: frame

When comparing the SL7 and SL8 side by side, differences may be subtle - most notably, the SL8 has a bigger headtube, lower dropped seat stays (by around an inch) and more rounded tubing - but Specialized claim performance upgrades are significant. At 685g (in size 56, a size 58 is 705g), it’s 15% lighter, there’s a 33% improvement in stiffness-to-weight ratio, and it’s 16.6 seconds faster over 40km than the next most aero road bike they’ve ever made (hard to check these numbers but check out their twenty-two White Paper to delve deeper).

The Specialized design team have put weight-saving learnings from the Aethos (which is a featherlight 585g in size 56) to work with the SL8, claiming it is the lightest frame on the world tour. All in, ready to ride (including Assioma DUO pedals) our size 58 tipped the e-scales at 7.145kg. 

Diving into the details, probably the most eye-catching new feature is the nose cone, which Specialized refers to as the ‘Speed Sniffer’. Deeper head tubes like this are quite common on aero-focused bikes - normally filling in backwards, like the Factor Ostro VAM -  however the SL8’s headtube bulges forward instead, allowing a sharper front edge to reduce drag. 

Although this has received some critique for its looks, I certainly didn’t baulk. Moreover, because it bulges forward, it allows the leading edge of the front forks to sweep back where they meet the headtube which I think looks fantastic, and it adds quite a unique aesthetic.

Other more suitable differences include the seat post, which is now not as deep. Their research claims that due to more turbulent airflow from leg disturbance, there is negligible benefit from an airfoil seat post shape. So this narrower seatpost and seat tube not only give a weight saving but offer 7% more compliance compared to the deeper SL7 seatpost.

There is a 32mm tyre clearance, which is more than ample for a bike of this nature.

Finally, just touching on looks, despite never having warmed to white frames before, I really fell for the pearlescent matt finish frame that I tested. It does mean you’ll need to clean it after every ride - no bad thing -as every little fleck of dirt does show up, and the Matt finish makes it harder work to get grease off. 

All Specialized’s frames come with a lifetime warranty which brings great peace of mind.

Specialized S-Works Tarmac SL8 review: seatpost, wheels and other components

Fitted with the new Roval Rapide integrated cockpit, it brings a 4w saving at 45 kph and a 50g weight saving compared to the older two-piece version. It is a single-piece design and is available in fifteen sizes.  It is great looking and very comfortable and the computer mount is very well executed, holding it perfectly horizontal to keep as aero as possible.

As standard, it comes fitted with a 52/36t crankset and an 11-30t rear cassette. This could be a little lacking for less strong riders, particularly if there are visits to steeper and longer alpine-type climbs. Cranks come mounted with a 4iiii dual-sided power meter.

The Roval Rapide CLX II wheels offer a suitable aero set-up whilst also being reasonably accommodating in crosswinds - they’re 51mm deep on the front and 60mm on the back. Although they both have 21mm internal width (which are optimised for 26mm tyres), external widths are slightly less conventional. 

The front wheel, with a 35mm external width, is particularly wide, and when fitted with the 26mm tyre that the bikes come with, there’s a couple of mm of wheel rim sticking out wider than tyre walls. At first, I thought this must have been some kind of mistake - it’s not something I’ve seen before - however, I soon learned the reasoning behind it and enjoyed the extra stability this brought when riding in crosswinds. 

The rear wheel is a more typical 30.7mm external width which matches the profile of the 26mm tyre much better. I switched the front to a 28mm - for some extra comfort, and this meant the bulge was less pronounced - and they will also accommodate 30mm tyres.

It comes shod with 26mm S-Works Turbo Rapidair 2BR - a well-regarded performance-orientated tyre.

Specialized S-Works Tarmac SL8 review: ride performance

Acceleration is immediate, which will largely be down to the combination of lightweight and aero, so it’s quick to get up to speed and also maintain it. 

I found handling to be brilliant across the board. Admittedly I’ve slowed down when descending since breaking my hip, so I wasn't able to put it through its paces too much here (but from hearsay, I understand that it is very planted). However, there’s no doubt that for riding fast - even on quite bumpy roads - and in crosswinds, I always felt assured. 

Despite its performance credentials, comfort was more than adequate too, the added touches of compliance here and there adding up to a noticeably smooth ride. There was never any sense of discomfort dismounting the bike after a long ride of several hours.

The cockpit has a textured finish to it, which offers a nice grip, and I found it comfortable with slightly splayed drop handles.

The 26mm tyres seem to buck the trend at the moment, with 28mm being the norm for that touch of extra comfort with little performance sacrifice - for potholed UK roads, at least - so this may well be an immediate substitution upon purchase for some.

Specialized S-Works Tarmac SL8 review: verdict

When it comes to an all-around package, it is probably the best bike I’ve ever ridden, and - call me fickle - but I really fell for its looks too, particularly in the white pearlescent finish. Surely no bad thing to covet your bike.

It never ceased to surprise me how lightweight it was, given its aero performance, and with such instantaneous speed pick up. It felt lightning fast and was always inspiring me to push on. What's more, it’s listed at £1,000 cheaper than its predecessor was, and although it’s clearly not a cheap bike, it undercuts a good number of rival brands’ top-end race bikes.

Be prepared for admiring looks from other cyclists and for KOMs to tumble. Is it really ‘one bike to rule them all’? If you want a bike that has got you covered to the max for all types of rides - as far as that is truly possible, as there are inevitably compromises for a multi-discipline choice - this is a fantastic choice.

Specialized S-Works Tarmac SL8 review: also consider

The Canyon Ultimate CFR Di2 Aero is a top-spec and highly regarded all-round race bike designed to excel at everything. Made from top-end carbon and equipped with flagship components - although arguably a notch down on a component or two, it’s equipped with their fantastic aero-integrated cockpit system and weighs a claimed 7.14kg, so is very comparable to the SL8. Coming in at £9,499, it is significantly cheaper than the SL8, which makes it a contender.

Handmade in the USA, the top-end ENVE Melee is another fantastic performance all-rounder, with excellent handling, and comfort yet race orientated too. However, with 35mm tyre clearance, and mudguard mounts, these are two particularly nice additional features which will be welcome to many club riders and bring greater versatility.