Specialized’s New Tarmac Disc Is Aero, Light & Ready to Rock
Weight: 6.65kg (claimed, size 54cm)
Style: Road disc race
Drivetrain: Shimano Dura-Ace Di2
Material: Carbon fibre
Tyre clearance (road): 28mm (any tire/rim combo that measures 30mm or less)
Specialized finally gave the Tarmac Disc a much-needed revamp for 2018. The new bike is a thoroughly modern update that relies substantially on the recently released Tarmac rim-brake model to create a top-flight road race bike with disc brakes that falls at or even below the UCI’s minimum weight limit requirements for pro racing.
What’s New for 2018?
Specialized had a conspicuous hole in its road racing lineup this year; while the Venge ViAS line has four disc-brake options; the Tarmac family had just a single, mid-priced model with aging technologies like quick-release wheels and an older frame design. It was a clear sign a new bike was on the way. The new Tarmac Disc incorporates much of the design work from the updated rim brake version announced in 2017, including aerodynamic tube shaping, but with the addition of 12mm through-axle wheel attachments, flat-mount disc brakes and even, on the top S-Works model, an integrated powermeter.
The Tarmac Disc Family
The S-Works is the first bike in the line to launch and will be available in stores in April. There are men’s and women’s versions, and it’s available as a complete bike or frameset only. Women’s bikes differ in touch points only: saddle and handlebar. There are other models planned, but those will not be available mid-year at the earliest, and Specialized shared no details of those at the S-Works launch. Based on the current Tarmac Rim lineup, expect between 2-4 additional Tarmac Disc models to be announced, not including women’s versions of those models.
What jumps out first is the weight. Specialized claims that the disc brake version of the Tarmac frameset is the same weight as the rim version. It’s a claimed 800-gram bare frame in the lightest paint. The lightest complete bikes are 6.36kg for rim and 6.65kg for the disc version, and Specialized claims all the extra weight on the disc version is in the wheels and components.
While the rim and disc bikes share the same design, there are some differences in tube shapes and layup to handle the different braking forces from discs. The layup is size-specific, and each frame has more than 500 individual plies, or pieces, of carbon that have to be precisely placed in a mould in the correct location and sequence.
Specialized set a benchmark in making the new Tarmac as aerodynamic as its original Venge aero road bike. The fork, downtube and seat tube shapes were all rethought with that goal in mind and re-done as truncated airfoils. The seat tube is the most aggressive, with a D-shaped cross-section and matching seatpost, with an internal clamp design to further aid aerodynamic efficiency. The seatstays are dropped and intersect the seat tube below the top tube, which lowers their overall exposed silhouette for a little bit more aero savings. Specialized says the effect is essentially the same as taking an older, non-aerodynamic Tarmac and switching the wheelset from conventional box-section rims to Roval CLX50 aero wheels.
As the flagship model, the S-Works Tarmac Disc spares no expense. The components are a complete Shimano Dura-Ace Di2 kit, Roval CLX50 Disc carbon tubeless-ready clincher wheels, and Specialized’s own FACT carbon fibre crankarms. But look closely: those cranks now have a built-in powermeter. The Power Cranks, as Specialized calls them, are claimed to be the lightest and most accurate powermeter in the world, and it’s stock on the S-Works.
The Tarmac Disc uses the same geometry from the rim-brake version. There are six sizes for men (49, 52, 54, 56, 58 and 61cm) and five for women (44, 49, 52, 54 and 56cm). If you’re a small guy, or you want a different paint job than the gender-specific complete bikes, the framesets are all available in seven sizes from 44-61cm. As race-oriented bikes, the Tarmac family is characterized by moderately long reaches and low stack heights.
Tight 41cm chainstays pull the rear wheel in close to the frame and provides for a shorter wheelbase. Head and seat tube angles are fairly comparable to race bikes from other brands, with fork trail intended to produce neutral to slightly fast handling. A growing trend in the bike industry is away from women’s-specific geometry, and Specialized joins that here. The Amira line is mostly gone now, and the women’s Tarmac Discs will feature different touch points and paint schemes, but will share the same geometry as the men’s bikes.