Lennard Zinn of Velonews Gives His Views On Riding the 2012 Specialized Tarmac SL4 and Venge

Tarmac SL4

The fun was just about to begin climbing up 17-Mile Rd. when I passed this point on the Tarmac SL4 and on the Venge the next day. Photo: Lennard Zinn

The go-to bike for Specialized pro teams in mountain stages now has a more balanced stiffness and ride feel front and rear, despite the fact that its predecessor placed 1-2 in last year’s Tour de France. Based on input from Specialized’s newest sponsored team, HTC-Highroad, changes have been made to a bike that has been refined over recent years based on input from Tom Boonen, Alberto Contador, the Schleck brothers, and their respective Quick Step, Astana and Saxo Bank teammates.
According to Specialized lead R&D engineer Chris d’Alusio, HTC riders remarked that the Tarmac SL3’s rear stiffness was perfect but that the front end of the bike was overly harsh. In response, Tarmac engineers went with a smaller (and lighter) 1-3/8-inch lower headset bearing on the SL4. (The Tarmac SL3 had a 1.5-inch lower bearing.) The new, shapely King Cobra head tube eliminates the flat sides of the head tube that could flex and replaced them with separated bulges to maintain rigidity despite the reduction in bearing size. By elevating the fork crown bearing race higher on the steering tube to bring the bearing more in line with the down tube, the engineering team could also trim material off of the back of the fork crown, making the fork ride less harshly while at the same time reducing weight-adding and strength-robbing bends in its carbon fibers.
Using data gleaned from lots of riding time on a strain-gauge-wired aluminum bike in varied conditions under multiple riders, including HTC’s Mark Cavendish and Bernie Eisel while at this year’s Tour of California, Specialized engineers developed a new lab test to evaluate bottom bracket stiffness that mimics the bending forces that the strain gauges recorded. The resulting changes in frame design grant the Tarmac SL4 a slight amount of additional bottom bracket stiffness while losing 57 grams in weight vs. the SL3.
I rode the new Tarmac SL4 (61cm size) on a testosterone-infused ascent and descent of the tortuous 17-Mile Road outside of Monterey, California, at Specialized’s 2012 product launch. I found it to climb great, feeling very snappy, stiff, and light. On the descent littered with reflective road “turtles” marking the yellow line as well as scary rectangular arrays of them serving as crosswalks, I was glad that the SL4 tracked so well. It was torsionally stiff enough to keep its wheels lined up where I intended during sudden swerves at high speed to avoid turtles. It railed the corners, and, happily, it was forgiving on the harsh impacts when I did hit road turtles. That smoothness continued on the rolling stretches through Pebble Beach and Spanish Bay golf courses, leaving me with a broad smile at the end of the ride.
Venge
Specialized’s first foray into the aero road bike category, the Venge, has gotten lots of attention since its WorldTour debut in Milan-San Remo where it came across the line first under HTC’s Aussie sprinter Matt Goss. And now Cavendish has gotten five Tour stage wins and a green jersey on it.
Like the Tarmac SL4, the Venge depends on a 1-3/8-inch lower headset bearing, in this case to provide adequate stiffness while creating a narrow profile for aerodynamic drag reduction. Special tube shaping throughout is done with aerodymics in mind. A flippable-offset aero seatpost allows significant fore-aft saddle position variation without added weight or aerodynamic drag. And at a 2,179g-gram weight for the frame “module” (frame, fork, headset, bottom bracket, crank and seatpost), the rider is not paying a significant weight penalty for the aerodynamic improvements.
The entire frame is narrower and taller in cross section than the Tarmac, but one particularly unique aerodynamic feature is the seatstay shape: a patented “cambered-cross-section-airfoil” that is flatter to the outside and curved on its inboard side. Since the upwind seatstay “sees” a higher wind speed than the other seatstay in a crosswind, the cambered-cross-section airfoil creates a smaller wake, and hence lower drag, than an angled-teardrop airfoil in the same crosswind. As a result of real-world testing on a track in Milan with Astana’s Roman Kreuziger, Specialized engineer and aerodynamic expert Mark Cote claims a four-watt power savings over the Tarmac in a crosswind at 40kph just for the seatstays, and a 20W power savings for whole bike. Riders within a peloton see lower wind speeds than the guys on the front, but they still face wind drag; Cote claims that even in the center of the peloton, they will get a minimum of four watts of power savings.
The Venge’s carbon layers are wrapped around a latex-dipped EPS foam (the same foam as in a bike helmet) mandrel in the shape of each frame subassembly (like the top tube/head tube/down tube subassembly), and then the whole shebang is put into the frame subassembly mold. The EPS shrinks down under heat, which allows air to circulate throughout the cured, airtight, latex bag. The mold is heated and air pressure is applied to compress the carbon layers together and eliminate air pockets. The fit of the foam mandrel in the mold is so exact that if a single ply is added or removed from the frame, the shape of the EPS mandrel must be changed accordingly.
Carrying this exacting frame manufacturing to even greater lengths, the (literally) Formula One (and high-dollar, low-production) version of this bike is the McLaren Venge, born out of collaboration between McLaren and Specialized.

The Venge I rode in Carmel Valley. Photo: Lennard Zinn

I took a Venge out on a four-hour ride in the Carmel Valley and over Laureles Grade back to the Specialized 2012 Product Launch in Monterey. While it is still quite a light bike that responds well to pedaling inputs, I think a rider would really have to drink the aero-testing Kool-Aid to choose it as his or her weapon of choice. I’m certain that you cannot feel the predicted aerodynamic benefit over, say, the Tarmac, and the only way to see it would be to test it on an indoor track with a power meter as D’Alusio and Boulder Center for Sports Medicine’s Neal Henderson did with Kreuziger. On the other hand, you don’t have to be particularly sensitive to feel the jarring while riding this bike on rough roads. The shoulder of the road in Carmel Valley is quite rough, and I couldn’t wait to get off of the Venge; it’s simply too harsh a ride for me, and I wouldn’t be able to outsprint Cavendish without a motorbike anyway.
Shiv
The redesigned Shiv time trial bike is now UCI legal and available for sale to consumers. Luc Callahan, head of road bike engineering at SBC, says, “We didn’t just remove the nose cone (that was banned by the UCI); we made other changes as well.” The new Shiv has an improved and re-shaped seatpost and seat tube, and it comes in five sizes (the bump on Contador’s Shiv behind the stem indicates that his is the smallest available size).
Amira
The S-Works Amira women’s race bike used to be the poor stepchild of the Tarmac, receiving the previous generation’s technology. Last year, the Amira used the technology and molding techniques of the Tarmac SL2, while that bike was on its SL3 generation. For 2012, the Amira incorporates all of the latest Tarmac’s technology, and the results it has attained with the HTC and CalGiant women’s teams are testament to the no-holds-barred engineering approach Specialized devoted to the bike. Specialized, pointing to race results, claims it to be the most dominant bike in women’s racing.
Like the Tarmac SL4, the flat sides of the Amira’s head tube have been replaced with bulged ones for stiffness. It has size-specific tube diameters throughout, smaller than the SL4, and its makeover has resulted in a 60-gram weight savings (to an 881-gram frame weight) over the 2011 Amira (women’s medium size). The module weight is 1,970 grams. The torsional stiffness (measured at the head tube) and the bottom bracket stiffness (using the new test mentioned above), as well as the torsional stiffness/weight ratio are all claimed to exceed those of competitors’ women’s bike models.