Stiffer, lighter, more aerodynamic – Specialized launches new Tarmac SL8

Latest in the Tarmac series makes its debut at the UCI World Championships in Glasgow

Clock14:17, Monday 7th August 2023
The new SL8 is Specialized's most aerodynamic bike ever.


The new SL8 is Specialized's most aerodynamic bike ever.

After multiple leaks and rumours over the last few weeks, Specialized has officially unveiled the new Tarmac SL8, and the American brand says it’s “the fastest bike in the world.”

It replaces the outgoing Tarmac SL7 that was ridden to multiple road race world titles, including by Remco Evenepoel last season, so it’s fitting that it was debuted by the defending champion along with a host of other riders in the men’s road race at the World Championships in Glasgow at the weekend.

Like the SL7, it has also followed the ‘one bike to rule them all’ motto, only this time Specialized has taken things to the next level, developing the bike in multiple key areas to make it lighter, stiffer, and more aerodynamic than its predecessor.

It also stacks up well against competitor bikes, as Specialized claims it’s the lightest bike “on the WorldTour,” not to mention the most aerodynamic bike the American brand has ever produced, overtaking the now-defunct Venge.

All of this amounts to a bike that, according to Specialized, is 16.6 seconds faster over 40 kilometres than the SL7.

With the SL8, Specialized hasn’t simply followed the ‘one bike to rule them all’ approach; they’ve taken it to the next level by developing the bike in multiple key areas.

More aerodynamic than the Venge

Up to the SL6 model, the Tarmac was Specialized’s climbing-orientated bike. That all changed with the release of the SL7, which was designed as a one-bike solution, suitable for any terrain.

This approach took the Tarmac down a more aerodynamic route to become an all-round race bike, also leading to the controversial discontinuation of the Venge, Specialized’s popular aero offering. This was a particular bugbear for many as, despite being more aero than the SL6, the SL7 didn’t compare so favourably to the Venge in terms of aerodynamics.

Anyone harbouring that particular frustration will be happy to hear that, according to Specialized, the new SL8 has stolen the crown from the Venge to become its most aerodynamic bike ever.

At first glance this claim may be surprising, as the bike features classic tube shapes rather than the deeper profiles found on all-out aero bikes, and it’s still easily identifiable as a Tarmac bike. Instead, these aero gains have been made by making changes to the front end of the bike where the biggest reduction to drag can be achieved.

Most notably, this includes a new head tube, or ‘Nose Cone’ as Specialized describes it, which is deeper than the one on the SL7 but also much thinner compared to other road bikes. The new design comes with a slight weight penalty, adding an extra 25 grams compared to the head tube on the SL7, but that, as we’ll see, is an outlier in the new design rather than the norm.

Beyond the head tube, Roval’s recently-released Rapide cockpit is also an important part of the equation. Unlike the previous iteration, it’s a one-piece bar and stem that Specialized says leads to significant aerodynamic gains.

As was also expected after images of the bike were leaked ahead of launch, the SL8 has a slimmed down seat tube, seatpost and seatstays. The chunky seatstays were one of the Venge’s trademarks that passed over to the SL7, but they’ve now been removed in favour of slimmed down versions. In a case of substance over style, Specialized says that the previous chunkier profiles had little to no aerodynamic benefits.

The seat tube is now so narrow that it’s the same width as the SL7’s seatpost. That, as you may have guessed, means that the SL8’s seatpost is also very narrow, so much so that Shimano’s Di2 battery pack no longer fits inside and is now mounted beneath it instead.

Lightweight without sacrifices

Making a bike lighter can be risky business. Losing the required material to shed grams can affect the aerodynamic profile of tubes and that’s a particular problem for Specialized with the Tarmac as, in order to achieve the one-bike-fits-all target, it needs to be both lightweight and aerodynamic.

To help, Specialized’s engineering team took inspiration from the American brand’s Aethos, one of the lightest bikes commercially available. It led to a minimalistic approach “to ensure there wasn’t a single gram of wasted material that wasn’t contributing to the frame’s stiffness, aerodynamics, and strength.”

As you’d expect, achieving this complex compromise is tough, and that’s highlighted by the fact that Specialized refined the design of the front triangle 53 times before landing on the desired combination of lightweight, aero and stiff.

The result is a frame that has a claimed weight of only 685kg (56cm) in its lightest build. That’s over 100g lighter than the SL7 and the majority of its competition too. For comparison, Factor’s newest O2 VAM, which is described by the brand as the “world’s fastest climbing bike,” tips the scales at 730g (54cm).

33% stiffer than the SL7

Completing the clean sweep of common marketing claims, Specialized also says that the SL8 has an improved 33% stiffness-to-weight ratio compared to the SL7. That’s number is inflated somewhat by the bike’s lower weight, although the American brand claims that its stiffness values surpass that of the departing SL7.

This stiffness varies per size as per Specialized’s Rider First engineering approach, which results in different levels of stiffness per frame size, helping to “ensure riders of all sizes have the same responsive ride quality, compliance, and stiffness when applying power.”

The other stuff

While some things have changed, many have stayed the same, including 32mm tyre clearance. There are also no changes to the geometry and the bike is available in multiple sizes from 44cm through to 61cm.

That’s for each of the different tiers, starting with the top-end S-Works Tarmac SL8, which is built from Specialized's Fact 12R carbon fibre. This is the lightest carbon layup that achieves the 685g frame weight, but the Pro and Expert models are constructed with Fact 10R carbon that comes with a 100g weight penalty.

Check out all of the builds available for the new Tarmac SL8 over on Specialized’s website.

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