Specialized Tarmac SL8 in-depth review - One bike that can do it all

Wave goodbye to specific aero or lightweight models, Specialized has combined the best aspects of the Venge and Aethos with the Tarmac to make the SL8 the fastest yet

The Specialized Tarmac is a bike that is synonymous with success at the highest level of the sport. Now in its eighth iteration, Specialized is not faced with the challenge of convincing people to buy a Tarmac, but instead decisions about where to take the bike next and how to make it any better. The recently released Tarmac SL8 is already being ridden in the WorldTour by the likes of Soudal-Quick-Step and SD Worx and has seen success, which is perhaps proof enough of its quality, but this is a bike that also needs to be attractive to the regular buyer, especially considering its price.

Perhaps outwardly the SL8 doesn’t seem radically different from its predecessor, the SL7, but delving into the details of the bike, there are some big improvements that Specialized has worked hard to make. A clear focus has been placed on aerodynamics, weight and ride quality on the SL8, with Specialized aiming to strike a balance where one is not sacrificed for another. Increasing a bike’s aerodynamic qualities through redesigned frame shapes and handlebars is becoming more limited as bike manufacturers are beginning to hit a ceiling with the number of shapes on offer – especially without sacrificing comfort and weight. With this in mind, it seems that where Specialized has taken the biggest step forward with the SL8 is in ride feel, proving the brand’s understanding of how a bike interacts with the rider. Just because a bike tests fast in the windtunnel, this doesn’t always translate into real world speed – Specialized seems acutely aware of this.

Specialized S-Works Tarmac SL8

I’ve spent the last month testing the Specialized S-Works Tarmac SL8 to really discover how the bike performed on the unforgiving roads of Kent and Surrey, UK. The S-Works model sits at the top of the SL8 food chain with the most premium carbon layup, my bike was equipped with Shimano Dura-Ace Di2 but the bike can also be purchased with SRAM Red. The Pro and Expert models use a lower grade carbon and come with either Shimano Ultegra Di2, SRAM Force or SRAM Rival on the Expert model.

Frame and fork

Specialized says it took 53 iterations to come to the eventual SL8 design, using what the brand describes as its ‘Front-Loading Development’ process. Using the layup strategy of the Specialized Aethos and Specialized’s FACT 12r carbon on the new Tarmac SL8 shape, engineers amplified stiffness in certain areas of the bike like the bottom bracket and head tube to try and create the most compliant ride possible. At the same time, focus was kept on ensuring that the SL8 frame remained lightweight, eventually coming in at 685 grams in a size 56 on the final and 54th iteration. The result is the SL8, which Specialized claims is “16.6 seconds faster over 40km, 15% lighter, 33% improvement in stiffness to weight and 6% more compliant than the 4X World Championship Tarmac SL7”.

Specialized S-Works Tarmac SL8

When it comes to the improved aerodynamics of the Tarmac, these are evident just by looking at the refreshed frame design of the SL8. Specialized says that its ethos is to put “aero where it matters, not just where it looks good”. The SL8 frame is much more slimmed down at the rear, where aerodynamics matter less. Specialized says that a “deep airfoil down tube and seat tube may look aero, but due to the dirty air they sit in, they create vanishingly small aero gains, but impact weight and ride quality significantly”.

With this in mind, the SL8 features a sharp leading edge on the head tube (coined the “Speed Sniffer”), made possible by the fact that the steerer tube has been moved backwards. This creates an overall much lower drag shape. The fork also bears a clear resemblance to the Venge fork (Specialized’s now discontinued aero road bike), with a wider crown and deeper blades on the legs. 

At the rear of the bike, the Tarmac SL8 seat tube is the same size as the SL7 seatpost meaning that the SL8 has the narrowest, most aero seat tube Specialized have ever made. This means that fast moving air around the legs can easily flow backwards leading to a more efficient ride.

Specialized S-Works Tarmac SL8

Of course, aerodynamics are less important as a bike is taken into the mountains, which means that keeping the Tarmac lightweight also had to be an important focus for Specialized during the design process of the SL8. Taking inspiration from the Aethos, which is currently the lightest production bike in the world, Specialized says it aimed to ensure that the SL8 was a bike that could perform well when the gradients kicked up but also was an extremely supple ride. At the skinny rear of the bike, weight has been shaved massively on the SL8, and the geometry of this section looks visually very similar to the Aethos. Specialized argues that the weight of the frame can be reduced when the bike isn’t trying to achieve the traditional aerodynamic look with deep tubing.


The SL8 retains the same, popular geometry as the SL7 and the same 32mm tyre clearance to give the bike an impressive amount of versatility. As with the SL7, the SL8 comes in seven sizes, 44cm to 61cm and the same frame is offered across all genders. This is in line with Specialized’s ‘Beyond Gender’ philosophy which argues that Retül fit data shows that creating male and female specific bikes is arbitrary.

There are a few differences in seatposts, while the SL7 comes with a 20mm setback as standard, with an optional zero-degree setback option, the SL8 comes with a zero-degree setback seatpost or a 15mm version which was fitted on the bike I tested. 

The build

As mentioned the Specialized S-Works Tarmac SL8 is available with either Shimano Dura-Ace Di2 or SRAM Red. My bike came equipped with the former, which I’ve reviewed extensively here. To summarise, the shifting speed is phenomenal, the braking power and control is as good as it gets, and the improved ergonomics of the hoods make things especially comfortable. I generally find Shimano shifting more intuitive than SRAM, though this could be influenced by the fact it’s more what I’m used to riding. My SL8 had 11/32 on the rear and 52/36 on the front which is a relatively standard set-up and versatile enough for a multitude of terrain – I believe a 52/11 is enough for most riders, though this could, of course, be upgraded to a 54/11 if needed. The bike also comes with a crank-based 4iiii power meter which is dual-sided.

Specialized S-Works Tarmac SL8

Plenty of the aero gains on the SL8 also come from the Roval Rapide cockpit that is fitted on the S-Works version of the bike, with Specialized saying that this shaves four watts of drag versus the two-piece Tamac bar and stem combination thanks to the minimised hardware on the front of the bars. Specialized offers 15 different bar and stem combinations with the integrated Rapide cockpit, informed by the brand’s Retül fit data. It’s worth noting that opting for the Rapide cockpit does limit the stem and bar sizing options on the SL8. For example, riders who prefer a more ‘old-school’ fit with a 140mm stem on a 56cm bike may now have to run a 115mm stem to achieve a narrower bar option. Pro models ship with the Tarmac SL7 stem/Roval Rapide handlebar while Expert models ship with the Tarmac SL7 stem/Specialized Expert Alloy handlebars.

Specialized S-Works Tarmac SL8

I was rolling with Roval Rapide CLX II wheels and S-Works Turbo Rapidair 26mm tyres. The front rim on the Rovals is 35mm wide and 51mm deep and is designed to keep the rider from over-correcting in crosswinds. At the rear, the rim is more traditional, 30mm-wide with a 60mm deep aero profile. Both wheels feature 21mm internal widths optimised for 26mm wide tyres – the tyre profile against the rim means it doesn’t bulge over which aids aerodynamics and also helps ride comfort and feel. The carbon layup on the wheels is intended to increase the impact strength of the rims by redistributing force away from the exterior of the rim, reducing the likelihood of tubeless blowouts.

Specialized S-Works Tarmac SL8

The Tarmac SL8 is fitted with a Body Geometry S-Works Power Saddle with carbon fibre rails – this saves weight but makes saddle switches more expensive if you’re testing multiple options. The full build I tested costs £12,000.

Ride feel

Although it can sometimes take some time for me to get used to a bike, I felt as if the geometry of the SL8 was extremely balanced and almost immediately on my first ride I was comfortable. Despite the lack of bar tape on the tops of the Roval Rapide Cockpit, the textured surface on the tops meant my hands felt secure with no risk of slippage. The shape of the bars suited me well too, with the radius from the tops to drops always giving enough wrist clearance both in and out of the saddle. When I was sprinting out of the saddle, the bars felt stiff and the front end was extremely responsive – I felt like nothing was wasted and the bike was certainly not giving way under any sprint load. Performance aside, the aesthetics of the handlebars are stunning, with a clean, polished finish that carries through the entire bike – though it should be noted that the full white version does involve plenty of cleaning.

Specialized S-Works Tarmac SL8

Once up to speed, the SL8 almost encourages you to go faster, accelerating extremely quickly – I found myself saving time on my usual ride routes without consciously making an effort to at all. This lively feel generally just made the SL8 fun to ride – knowing I was going to be heading out on it made it easier to get out of the door and on a ride each morning. Riding in and around London there are always plenty of traffic lights and moments that require stopping and accelerating again to get up to speed, and I felt like the SL8 made this easy – I just wasn’t feeling that build-up of fatigue as quickly as I do on other rides through these constant changes in speed.

On long, flat sections of road the SL8 holds speed extremely well, helping me get on top of the gear and put out better power as a result. Compared to some deeper profiled, pure aero road bikes I’ve used, the SL8 has a different feel when up at speed. I didn’t think it descended quite as quickly on an arrow straight section of road, but this was extremely marginal and I certainly would not sacrifice the incredible handling and light weight of the SL8 for this small gain. Some pure aero bikes with thick tubing feel slow and heavy around corners, but the SL8’s narrow frame shape at the rear and on the seat tube were extremely compliant – there was no need to battle the bike to get it to go where I wanted it to, the SL8 moved with me and supported the line I wanted to take.

Specialized S-Works Tarmac SL8

I understand that, visually, the SL8 doesn’t look too different from the SL7, but I do believe that Specialized has trumped the predecessor by creating a bike that can truly do it all. It’s more aero than the discontinued Venge and it is strides ahead of that bike in terms of weight and handling, and it’s almost as light as the Aethos but offers much better responsiveness and stability on the flat. It’s as if Specialized has taken the very best of the Venge, Tarmac and Aethos and combined them to create a super-bike that really has very little to be faulted on. The SL8 is obviously priced at a premium, but for a top-spec 'super bike' I don’t think that £12,000 is an outrageous asking price, especially compared to other brands on the market that offer builds with similar components.


I’d like to be able to better balance this review with some points of improvement for the Tarmac SL8, but I have struggled to find much wrong with the bike. Specialized has hit the nail on the head in almost every department: the bike is lighter, more compliant, more aerodynamic and feels fantastic in a way that is hard to put into words. The Tarmac SL8 simply gives free speed, and evoked the same kind of excitement in me about going on a bike ride that I had when I very first started out in cycling.

Perhaps there are pure aero bikes that might test slightly faster in the wind tunnel, but the Specialized Tarmac SL8 trumps everything that I’ve ridden in terms of how it acts in the real world. While Specialized has provided all the necessary impressive data to prove the aero qualities of the SL8, this isn’t what I would lean on as the selling point for this bike. Where it stands out from the crowd is in how it makes you feel and the added confidence it gives the rider. For racing and riding fast on all terrain and in all conditions, you’d be hard pressed to find a better option than the Tarmac SL8. It’s a big investment, but it’s certainly the only bike you’d need for road riding in your collection. 

Shop now