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By Lennard Zinn
Fabian Cancellara’s time trial bike time trial bike that he raced in the Tour de Romandie, the Giro d’Italia, and the Tour de Suisse now has a name: The Shiv.
Unlike shivs used in prison riots, this is hardly an improvised weapon slapped together out of found items. Engineers have thought out every detail on this bike and tested and simulated it for its contribution to the bike’s overall aerodynamic efficiency, stiffness, and strength. And the materials and the processes required to make it are extremely expensive.
The Shiv came out of Specialized’s Project Black, the company’s name for special projects for its pro teams. As Specialized engineer Luc Callahan says, “The number one benefit we get from sponsoring teams is R&D. Sure, victories are great – like the six national road championships we won today (June 28), but it’s what we learn from the riders that we value the most.” Much equipment created in Project Black never becomes commercially available and may even be abandoned before it is ever raced. The Shiv, however, will be available to the market in spring 2010, with price, quantities and timeline yet to be determined.
Looking at the Shiv, it is pretty obvious that it is an extremely aerodynamic bike. But it may not be so obvious that it is also an extremely stiff bike as well as being quite light, which are features that have not escaped the attention of the rider also known as “Spartacus.”
By tying together the top and bottom of the steering tube with the nose cone (into which is mounted the bars and the front brake), and by making the head tube not only extremely deep but also quite wide for an aero’ bike, Specialized’s engineering team has managed to make the front end of the Shiv stiffer than the stiffest of its road bikes (which are quite stiff). And the entire bike, even with a 900-gram rear disc wheel on it, weighs in at a mere 16.8 pounds.
Generally, there are two ways to make a bike aerodynamic: to make it skinny and to shape it to reduce drag. Since the UCI’s 3:1 mandated maximum aspect ratio does not allow for an ideal airfoil shape, skinny is the first item of business. So, this bike got a thin, one-inch steering tube (slightly flared at its base for a 1-1/8-inch lower bearing), which is certainly no way to start if you want to make a stiff front end. But the nose cone has a forged aluminum section at its top bolted to the top of the steerer, and the bottom of it is bolted to the underside of the fork crown with a broad, stiff, carbon plate. That ties the whole structure together with the top and bottom of the steering tube and makes it very stiff. Bolting the carbon plate underneath also increases the stiffness of the tiny cantilever brake hidden inside the nose cone, whose pivot bosses are part of the nose cone, not the fork. The brake has a stiffening arch within the nose cone and is tied rigidly to both the handlebar and the fork, thus transferring the braking force directly into the bike.
While skinny makes for good aerodynamics, wide is a must for stiffness and stiffness/weight ratio. Specialized optimized the bike for a 12.5-degree yaw angle (the net wind direction – a vector combination of the rider’s speed and direction and the wind’s speed and direction), indicating a fast rider in a crosswind. The company’s goal was create a bike that produces less than 500 grams of drag at 30mph at 12.5 degrees of yaw and less than 550 grams at zero degrees (indicating no wind or a wind along the direction of the bike). Those are numbers well under those of the Specialized Transition triathlon bike.
In a crosswind, to get the air to adhere to the head tube’s surface (that’s the fastest aerodynamically – when the air sticks to the surface rather than swirls off turbulently), it is actually a benefit for the nose cone and head tube to be wide, so that the wind coming from the other side of the bike can wrap around it. So in this case, the goals of both aerodynamics and a high stiffness-to-weight ratio are achieved by making a large, thin structure at the head tube and nose cone. Incidentally, Specialized claims drag results for the Shiv at zero degrees of 513 grams, and at 12.5 degrees of around 420 grams. Goal met.
Another goal was to have no drag increase with a higher handlebar position. That’s impossible on most bikes, because it would mean a higher stem and hence a longer steering tube, and cylinder drag on an extended steering tube is significant. Specialized achieved this as well.
Key to this system is a base bar that is always the same height, as it is fixed into the top section of the nose cone. Adding aero’ shim pieces and stacker pieces lifts the aero’ bar and elbow pads to the desired height. And a plate bolted across these two aero-shaped columns coming up from the base bar builds rigidity into the bars, regardless of height.
While many aero’ bars have only small horizontal handles, Specialized built the Shiv’s bar with a hook to the end, extra drag be damned. This was in response to feedback from pro riders, some of whom had crashed in the past on time trial bikes when going from the aero’ position to the braking position and missing a tiny handle. They wanted real handles with enough length to grab without fear. And in the interest of further safety, engineers built what they think to be the strongest, stiffest production aero’ bar for the Shiv. If you saw Cancellara hop a median strip in the final time trial on his way to overall victory in the Tour de Suisse, you will not have any doubts about these characteristics. Specialized is developing its own little aero’ levers for these bars which have barrel adjusters sticking straight out in front with the cable head, since there is no room for an accessible barrel adjuster on the little cantilever brakes inside the nose cone and under the bottom bracket.
Originally the brainchild of head of bike R&D Chris D’Alusio, the Shiv’s development monopolized more than 100 wind tunnel hours (mostly at the University of Washington wind tunnel and the A2 wind tunnel in North Carolina) and umpteen computer hours performing computational fluid dynamics (CFD) simulations.
Chief aerodynamics engineer Mark Cote’s love for CFD intertwined with D’Alusio’s love for using pieces of yarn along the bike’s surfaces to observe air pressure drops, turbulence and air movement directions, and with aerodynamics guru Chester Kyle’s (chief of Project ’84 and Project ’96 US Olympic aero’ bike projects) use of a stethoscope with a thin wand held along the bike’s surface (it’s quiet where the airflow is smooth and noisy where it’s turbulent). They also used “China Clay” paint – a mixture of chalk and kerosene – to observe airflow in the tunnel.
Another takeaway from these studies was moving the down tube as close as possible to the front wheel; the dummy bike in the tunnel utilized a fork with multiple dropout positions to allow moving the wheel closer to and further from the down tube. Turns out, closer is faster, especially with the big tube shape they had chosen to provide stiffness and to best meld with the shapes of the head tube, nose cone and fork crown.
A one-piece monocoque bottom bracket/chainstay assembly similar to that on the new super-stiff Tarmac SL3 road frame, gives the Shiv great rear-end stiffness. New molding methods required to pull this off as well as to create the precision of the skirt of the nose cone, which stays close to the head tube yet doesn’t scrape on it, are very expensive, another reason not to expect the Shiv to fall within your budget when it does reach the market.
The Shiv is super stiff for a TT bike – it has torsional stiffness almost equal to that of the Tarmac SL2, a bike universally praised by Saxo Bank riders for its stiffness. That this stiffness comes without high weight or drag numbers is a supreme accomplishment, to the point that Specialized marketing manager Ben Capron has thrown down the gauntlet and challenged any other UCI-compliant ProTour production TT bike to a head-to-head wind tunnel test to establish bragging rights.
The fitting on the Shiv takes a different tack than most, and not only for the method of stacking up the aero’ extensions and tying them together. The four frame sizes all have the same seat tube length and rear end. What changes is the length of the stiff, 100g seatpost (which is straight – thanks to a standard seat-tube angle on the frame) and the length of the front end. The cockpit lengths from the vertical line through the bottom bracket to the center of the handlebar will be 456, 471, 486, and 506mm, and they may be sold that way as the sizing indicator.
So where does this leave the Transition, a bike which Specialized touted as so aerodynamically advanced just a few years ago? The Transition will continue being sold as an aero’ bike, but it will be targeted more for triathletes, as its price, ease of changing handlebars and other components, more comfortable, less stiff ride, and six frame sizes (three new ones for 2010 – an XS size and two more on the tallest end) are well suited to that sport.
Zinn’s regular column is devoted to addressingreaders’ technical questions about bikes, their care and feeding and how weas riders can use them as comfortably and efficiently as possible. Readerscan send brief technical questions