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The Specialized S-Works Tarmac SL4 Di2 is an incredible feat of carbon engineering with its immensely rigid structure. Front triangle stiffness is especially awe-inspiring. But no, that's not a Dirk Hofman motorhome in the background.
"Otherworldly stiffness and reasonable comfort but cries out for better wheels"
Otherworldly stiffness and reasonable comfort
This article originally appeared on BikeRadar
Specialized has injected a bit more comfort into its latest S-Works Tarmac SL4 relative to last year's SL3 but in every other way it's an unbelievably rigid and surgically precise machine – not to mention superlight, too. Racers will love it for sure but even enthusiast riders who prize all-out performance above all else will definitely want this on their short list.
Ride and handling: ultra-precise and very nimble but with reasonable comfort and stability
The S-Works Tarmac SL4's defining characteristic far and away 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 that remarkable solidity is detectable even with more subtle commands. Think of it this way: unlike even slightly softer bikes that essentially 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.
As expected, that level of stiffness and efficiency doesn't exactly 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 yes, big bumps are definitely tough on the body particularly after long days in the saddle.
Unfortunately, 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 but 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 more wooden feel unlike livelier rides that may deflect more but also tend to have just a touch more springiness.
The scale also proves the S-Works Tarmac SL4 to be very light with our 52cm tester coming in at just 6.64kg (14.64lb) without pedals – not bad when you consider the Dura-Ace Di2 group and Roval wheels to be light but not extremely so.
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 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.
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 seat stays. Whereas small custom builders have long touted the virtues of roundish tubing while some bigger names instead went with more wild shaping, 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.
Specialized has received criticism in the past for plastering a few too many logos on its top-end machines and in that respect, the black-and-white finish on the 2012 S-Works Tarmac SL4 is comparatively subtle. Take away the giant 'Roval' logos on the wheels (we'll get to those shortly) and what you're left with is a tasteful dual-texture gloss-and-matte black base with a few plain white 'Specialized' and 'S-Works' logos – still too much for some but still reasonable in our book.
One curious oversight is the mount for the Shimano Dura-Ace Di2 battery. Instead of building a dedicated mount into the frame, Specialized instead uses the standard long-format cradle that bolts to the down tube water bottle bolts. However, the lower edge of the mount is secured to the down tube with a lowly zip-tie – an unforgivable sin in our opinion given the bike's flagship status, not to mention cost.
Actual weight on our 52cm frame is just 920g (with seatpost collar, rear derailleur hanger, and water bottle bolts) with the all-carbon tapered fork adding just 310g (180mm steerer, without compression plug) more – solid numbers on their own but even more impressive when the phenomenal chassis is taken into account.
Sorry, Specialized, but we really expect to see something more elegant than a zip-tie to hold the end of the battery mount down on a bike costing US$11,000
Equipment: awesome Dura-Ace Di2 shifting but only so-so wheels
We've gone at length on the excellent performance of Shimano's Dura-Ace Di2 electronic group so we'll spare you the details. Rear shifts are as impeccable precise, accurate, and smooth as ever and despite not using Shimano's ultra-stiff chainrings, front shifting is exceptional as well. Braking performance is superb as in other samples we've tested, too, with a firm and communicative lever feel, gobs of power, and very good modulation.
Specialized outfits the S-Works Tarmac SL4 with a smattering of components from its own parts bin and for the most part, it's all quality stuff befitting a top-range bike. The carbon railed Romin Pro saddle is lightweight yet supremely comfortable, the FACT carbon seatpost is bulky and a bit awkward to adjust but lightweight and secure, the semi-anatomic carbon handlebar complements the frame stiffness well and boasts a versatile bend, and while it's not particularly svelte, the forged aluminum stem is stout and is conveniently adjustable for angle via Specialized's trick offset shim system – no complaints for the most part.
We were disappointed in the stock wheelset, though. The Roval Rapide SL 45 aluminum-and-carbon clinchers certainly look the part with their bold black-and-white graphics, usefully aero 45mm-deep rims, and smooth-rolling hubs (bolstered by DT Swiss rear internals). However, they're not especially light at nearly 1,600g a pair nor are they that rigid under power, which goes directly against the frame's strongest performance advantages.
Making matters worse is that they don't ride all well, either. Even with outstanding Specialized S-Works Turbo tires fitted – one of our favorites – the wheels make the bike feel more sluggish than with any number of other reference wheels we swapped in and they don't ride very well, either. In fact, we traded in a set of Powertap's new carbon clinchers built with 45mm-deep Enve Composites rims and not only gained a power meter and vastly improved ride quality but lost both static and rotating weight in the process.
Frankly, a chassis this good deserves wheels much, much better than these and unfortunately, Specialized is likely going to have to look outside of the company catalog to get it done considering the stock Rovals are currently the best in its range.
Wheels aside (and that zip-tie blight), the Specialized S-Works Tarmac SL4 is a worthy flagship with chassis stiffness that needs to be ridden to be believed. The US$11,000 price tag of our Di2-equipped testers will of course put it well out of reach of most consumers but thankfully, Specialized also offers the same frameset with SRAM Red for US$7,700 or the slightly downgraded 'Pro'-level frameset for as low as US$5,300 with a SRAM Red/Force mix.
Weight: 6.64kg (52cm, complete, without pedals); 930g (frame only with seatpost collar, rear derailleur hanger, and water bottle bolts); 310g (fork only, 180mm steerer tube, without compression plug)
Available sizes: 49, 52 (tested), 54, 56, 58, 61cm Pros: Incredible chassis stiffness, reasonable comfort, superb Dura-Ace Di2 group
Cons: So-so wheels
Cyclingnews verdict: 4 stars
More information: www.specialized.com
Frame: Specialized S-Works Tarmac SL4
Available sizes: 49, 52 (tested), 54, 56, 58, 61cm
Fork: Specialized S-Works FACT carbon, 1 1/8-to-1 3/8in tapered
Headset: Integrated 1 1/8-to-1 3/8in tapered
Stem: Specialized S-Works ProSet
Handlebars: Specialized S-Works Tarmac, shallow drop
Tape/grips: Specialized S-Wrap Super Light
Front brake: Shimano Dura-Ace BR-7900
Rear brake: Shimano Dura-Ace BR-7900
Brake levers: Shimano Dura-Ace Di2 STI Dual Control ST-7970
Front derailleur: Shimano Dura-Ace Di2, FD-7970
Rear derailleur: Shimano Dura-Ace Di2, RD-7970
Shift levers: Shimano Dura-Ace Di2 STI Dual Control, ST-7970
Cassette: Shimano Dura-Ace CS-7900, 11-25T
Chain: Shimano Dura-Ace CN-7900
Crankset: Specialized S-Works FACT, 53/39T
Bottom bracket: Specialized OSBB integrated, hybrid ceramic bearings
Wheelset: Specialized Roval Rapide SL 45
Front tire: Specialized S-Works Turbo, 700x23c
Rear tire: Specialized S-Works Turbo, 700x23c
Saddle: Specialized Body Geometry Romin Pro
Seat post: Specialized S-Works FACT carbon