Specialized S-Works Tarmac SL4 Di2 £8500

Otherworldly stiffness

BikeRadar score 4.5/5

Specialized have injected a bit more comfort into the 2013 S-Works Tarmac SL4 relative to 2012's SL3 but it's still an unbelievably rigid and surgically precise machine – not to mention super light, too. Racers will love it for sure, but enthusiast riders who prize all-out performance above all else should also add it to their shortlist.

Note: we have reviewed this bike in two guises, the main difference being in the wheelsets. This review is based on our testing of both bikes, with the spec and lead image being the latest version of the bike. Many of the photos in the gallery are of the previous version.

Ride and handling: Ultra-precise and very nimble but with reasonable comfort and stability

The S-Works Tarmac SL4's defining characteristic is its incredible chassis stiffness, and not just the usual bottom bracket variety. Sure, the drivetrain efficiency is fantastically high, with the usual benefits in terms of sprinting and climbing but on an even greater scale in this particular case. Few bikes we've ridden feel so utterly flex-free from end to end.

That amazing full-frame torsional rigidity is most noticeable when you're violently wrenching the bike and out of the saddle, but it's detectable even with more subtle commands. Think of it this way: while even slightly softer bikes have a 'filter' between your inputs and the reactions, the S-Works Tarmac SL4 has no such thing. 

Handling in general is awesomely precise and when combined with the bike's appropriately racer-steep angles, you'd better mean it when you move the bars because you can be assured the bike will react in kind. 

Out on the road, the long, low position and super aggressive handling can make it nervy on climbs. Get it on a descent and the reverse is true. We went looking for the best technical descents and hit stretches of fast road to push the Tarmac's handling limits.

Downhill it feels planted, with a tenacious amount of grip on offer through fast corners. It reacts quickly to the slightest of inputs. You feel that a twitch of your shoulders is enough to switch lanes and attack; it has an almost telepathic response to rider input. We never got to a point where the SL4 felt out of its depth - testament to how exciting it is.

As expected, that level of stiffness and efficiency doesn't come paired with best-in-class comfort levels, though it's still pretty good for a dedicated race bike. High frequency road buzz is handled well but big bumps are definitely tough on the body, particularly after long days in the saddle.

That off-the-charts rigidity also means the S-Works Tarmac SL4 doesn't track less-than-perfect pavement as well through corners as frames that have a little more give to them, though the low bottom bracket (71.5mm drop on our 52cm tester) at least partially offsets that by lowering the center of gravity. The lack of flex also lends a wooden feel compared to livelier rides that may deflect more but tend to have just a touch more springiness.

The top tube and down tube wrap around the tapered head tube to lend more torsional stiffness to the front triangle. The lower bearing diameter has decreased to 1-3/8in for a little extra comfort relative to the SL3

Frame: Light and stiff with lots of shaping

That the front triangle of the S-Works Tarmac SL4 is so stiff should come as no surprise when you consider the frame dimensions. Specialized have downsized the lower steerer tube diameter to 1-3/8in from 1-1/2in on the Tarmac SL3 to shave a few grams but the surrounding pipes are bigger than ever. 

Specialized claim the new SL4 FACT 11r carbon frame is their best yet. They also claim it has the highest stiffness-to-weight ratio of all the bikes in their range.

The down tube tapers from 55mm across at the bottom bracket to an insane 66mm across up front while the top tube hits its maximum 62mm width just behind the stem, partially wrapping around the head tube and lending more support to that critical area. If the numbers on paper aren't impressive enough, consider that the fork crown measures barely broader at 85mm – or just compare these figures with your current machine.

Aside from the round-to-rectangular profiling of the seat tube, most of the rest of the S-Works Tarmac SL4's frame tubes are nominally ovoid, with the exception of some flattening on the seatstays. Small custom builders have long touted the virtues of roundish tubing and while some bigger names have gone with more wild shaping in the past, it seems that most of the industry is now coming into agreement.

Other details on the S-Works Tarmac SL4 frame include trick tubular carbon fiber dropouts, very tidy internal cable routing that works with either mechanical or electronic drivetrains, and Specialized's own OSBB oversized bottom bracket – essentially an offshoot of PressFit 30.

Equipment: Awesome Dura-Ace Di2 shifting

This model features full 11-speed Dura-Ace Di2, along with modern, wider-rimmed, full carbon clinchers. As you’d expect from a bike of this stature, no expense has been spared when it comes to the components. It gets lightweight carbon all the way from a host of S-Works parts.

The Tarmac is a bike you’re expected to live up to and that's apparent in its off-the-peg spec. An 11-25 close-ratio 11-speed block at the back makes it adept at accelerating. There are no significant jumps as you progress up or down the cassette, so Dura-Ace Di2’s continuous shift feature can be easily exploited. Specialized have also adopted Shimano’s internally mounted battery (in the seat-tube), which makes for a super-clean looking machine.

The 53/39 combination of the S-Works cranks makes it a bike for the strongest of climbers. Any shop worth its salt should change something like a cassette and chain to suit your needs at no extra charge. This is especially true if you're dropping the price of a new car on it.

The Roval CLX 40 wheels are a marked improvement on the SL 45s that were specced on a previous test model of this bike. They are 40mm deep Roval wheel and, shod with brilliant 24mm S-Works Turbo tyres. With a wider-than-standard shape, a gummy tread and supple carcass, they're a match for Schwalbe’s Ultremos or Conti’s GPs in performance terms. SwissStop carbon brake pads combine with the grippy tyres to provide great power and consistent feel.

The sloping frame leaves a lot of exposed seat post, providing comfort-aiding flex, plus it's topped with Spesh's great Toupé saddle. At the front, the oversized, tapered head tube and burly SL4 fork are super-stiff, but noticeably light. The front end solidity can make the Tarmac fatiguing – we’d opt to fit Specialized's own super-comfy Bar Phat tape to counter that. While it's not particularly svelte, the forged aluminium stem is stout and is conveniently adjustable for angle via Specialized's trick offset shim system – no complaints for the most part. 

Our only other niggle is with the S-Works carbon chainset, and we appreciate its stiffness, low weight and styling. However, the S-Works rings can’t match Shimano’s Dura-Ace ring profiles for chain engagement and speed of shift. Even accounting for the fact that it's running the otherwise flawless Di2 setup, the S-Works chainset doesn't quite match the Dura-Ace equivalent.

The Specialized S-Works Tarmac SL4 is a worthy flagship with chassis stiffness that needs to be ridden to be believed. It is adept at going very quickly. It's a fast hitting brute: furious, frantic and quick to get the job done, making it as good as a race bike gets. This focus can also be a downside. You need to be an elite racer, or at least an aspiring one, to get the most from it. If that sounds like you, then this bike puts a phenomenal package at your disposal.

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