This story originally appeared in the March/April 2011 issue of Inside Triathlon magazine.
Since the Cervelo P2K—one of the first production bikes with airfoil-shaped tubes—gained popularity, mainstream triathlon bike manufacturers have steadily replaced the round tubes traditionally found on road bikes with shaped ones that create less aerodynamic drag. A vertical cylinder creates five times the wind drag of a teardrop-shaped object of the same size, according to research done by Sighard Hoerner in 1965, so every vertical tube that is not aerodynamically optimized slows the bike dramatically.
The P2K was significant because of its aerodynamic downtube and seat tube (and tri geometry), but tweaking and tuning every section of the frame from the head tube to the seatstays to minimize wind drag has become standard. Not all manufacturers agree on the best aero design, but the round tube has nearly disappeared from contemporary triathlon bikes. That is, except for the steerer tube and stem. These aerodynamically archaic components have survived because they form a reliable and highly adjustable handlebar attachment system, but they must be replaced for a bike to jump to the next level of aerodynamic efficiency. The newest generation of tri bikes, including the Scott Plasma Premium, does exactly that.
Minimizing the aerodynamic drag created by the frame is critical to performance, but it makes up only a small fraction of the total drag created by the bike and rider in combination. Aerodynamic resistance generated by the entire system must be reduced to maximize speed, and the rider’s position has a massive effect on wind drag. But rider comfort is arguably even more important to race-day performance than aerodynamics, so a bike must be comfortable and fit well.
Scott did not reinvent the handlebar attachment system when designing the Plasma 3. Instead, it controlled the way the stem is positioned on the frame. The steerer tube is one of the last remaining vertical cylinders found on many modern tri bikes, and its round shape generates unnecessary wind drag, especially if it protrudes high above the frame to prop up the aerobars. Scott removed this protruding cylinder by forcing the stem to mount directly on top of the frame without any spacers.
Designers further integrated the stem into the frame by elevating the top tube to fill in the space behind it. Scott offers four compatible stems, and this range of choices creates 1.5 cm of fit variability in the fore-aft direction and 4 cm in the vertical. All four stems are within the range most bike fitters consider acceptable to maintain a bike’s handling characteristics. Standard aftermarket stems cannot be used on the Plasma 3, and this restriction eliminates the option of shoe-horning a rider onto the bike with an extreme stem or spacer stack. Although this limits the number of riders that can fit a Plasma Premium, it also prevents a rider from ruining his bike’s handling characteristics with an ostentatiously tall spacer stack or freakish stem. In some ways, this restriction will save some triathletes from their lust for a bike that isn’t an appropriate match for them.