Specialized Tarmac Expert SL4 Di2 - detailed description

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Specialized Tarmac Expert SL4 Di2 – first look

Spring is finally upon us and we can at last feel justified in testing a machine freed of the necessity to stand up to inclement conditions and concentrate on speed and riding pleasure.

Enter the Specialized Tarmac SL4 Expert SL4 Di2, a machine we regarded with interest on our February excursion to Mallorca, when we were invited to observe Team IG-Sigma Sport’s pre-season training camp. The boys in red and black use the Expert as a training model (they roll out on top-tier S-Works machines for competitive engagements) and we fancy it’ll stand up to our, ahem, less demanding (read: slower) riding style.

So what do we have? A chassis fashioned from Specialized’s FACT IS 10r carbon, dressed in a combination of Shimano Ultegra Di2 components with an FSA SL-K Light chainset, and rolling on DT Axis 4.0 hoops, shod with Specialized’s Turbo Elite rubber. Let’s take a closer look before we begin the serious business of testing.

The Specialized Tarmac SL4 Di2

Contemporary carbon frames can tend to a similar design: take the stickers from some and you’d struggle to tell them from their rivals. Not so with the Specialized Tarmac Expert, whose silhouette is notably different from many we’ve seen.

For a start, the men at Morgan Hill have placed the girth at the front end of the bike, rather than at its centre. Nine out of ten machines will have an oversized down-tube that becomes steadily more, well, oversized as it journeys from head-tube to bottom bracket. The Specialized Tarmac Expert does the reverse.

The down-tube swells to a massive 70mm diameter as it meets the head-tube, and while it’s hardly slender at the bottom bracket, where it tapers to a still hefty 50mm, have Specialized concluded that the greatest force will be exerted at the front of the bike and deployed greater carbon resource there? The head-tube, pitched at a no-nonsense 73 degrees, is a similarly chunky affair, with a side profile some 50mm deep, providing ample accommodation for the 1-3/8” inch lower bearing, and the top-tube is 60mm as it joins the head-tube. Throw in a robust looking, full-carbon fork, 50mm broad in the leg at its widest point, and you have a pugnacious-looking steed with the air of prize fighter. Will it be similarly aggressive? Time will tell.

While the aforementioned bottom bracket shell is smaller than some, essentially a neatly moulded junction of down and seat tubes, the chainstays pick up the oversized theme evident at the front of the bike, emerging from the bottom bracket some 50mm deep and reducing only to 20mm at the drop out. Have Specialized judged that the chainstays play the greatest role in converting pedaling forces to forward motion (more, say, than the bottom bracket shell on this showing) and allocated their resources accordingly? We’re keen to find out.

Their take on seat stay compliance (along with stiffness in the lower third of the bike, the goal of every designer) is interesting, too. The Tarmac Expert SL4’s seat stays, the area responsible (or not, ideally) for transmitting shocks from the road to your rear end, pass either side of the seat-tube in an elegant swoop, offering clean lines and, perhaps, compliance. We’ll let you know.

Specialized Tarmac Expert SL4 Di2 – head tube

The 52cm chassis has a low and compact appearance. This visual impression owes much to the extremely short head tube: at 120mm, one of the lowest we’ve encountered; lower even than the 125mm offering on the Kinesis Racelight TK3. Measuring the SL4′ seat-tube revealed a seat-tube of 49cm that placed its junction with the top tube at 71cm above the ground. With the saddle set at our customary 71.5cm from the bottom bracket centre, a gap of some 150mm between saddle nose and top tube opens up. We’re hoping this apparent lowness will translate to greater manoeuvrability: a machine we can throw around.

There’s plenty of pleasing details here, too. The Di2 battery is tucked as unobtrusively as any we’ve seen, on the underside of the bottom bracket shell, and the internal routing of the electronic cables is very subtle, emerging from the lower portion of the seat tube for the front mech and at the end of the driveside chainstay for the rear.

We’d be disappointed to see corners cut in spec-ing a machine with a £4,000 price tag, and our previous acquaintance with much of the kit supplied here fills us with hope.

The groupset is Shimano Ultegra Di2 in all but chainset, where Specialized have replaced the Japanese giant’s second from top offering with an FSA SL-K Light. This hollow-armed carbon offering with CNC-machined aluminium chainrings is a high-quality turbine and attractive to boot. In the BB30 configuration supplied here, it weighs a claimed 614 grams, significantly lighter even than the latest incarnation of the Ultegra chainset.  We’ll say again now, however, as we say always – why not deploy the groupset in full? We know Shimano (and SRAM, and Campagnolo, come to that) design its components to work together. Minor gripe aside, the SL-K is a fine looking implement, and Specialized have rightly deployed it with 52-36 ratios.

Specialized have substituted a carbon-armed FSA SL-K turbine for the Shimano Ultegra turbine that would have matched the remainder of the groupset

The finishing kit is Specialized’s own, with an alloy Tarmac Expert handlebar, a Comp 6061 alloy stem, Comp carbon seatpost, and Toupe flow saddle. Each component is new to us, so we’re unable to offer a hint at performance at this early stage. We’d prefer to see a 40cm handlebar on a 52cm frame, rather than the supplied 42cm, and the 90mm stem is likely to be swapped for our preferred 110mm unit, but these may be little more than personal preferences.

DT Swiss provide the wheels. They’re Axis 4.0, a modest aluminium clincher with 24 radially-laced spokes up front and 30 in the rear, where they’re set out in a fairly conventional style: nine laced radially on the non-driveside and 20 in a two-cross pattern on the driveside. The rubber is Specialized’s Turbo Elite, billed as a promising 100tpi on the Expert SL4 Di2’s spec sheet, but as 60TPI on its own page on Specialized’s website. We’ll judge the suppleness for ourselves.

The Specialized Tarmac Expert SL4 Di2 will be our steed of choice throughout the month of May. Check back soon for a full review.

Discuss in the forum

Website: Specialized
Size: 49, 52, 54, 56, 58, 61
Price: £4,000

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