But the wheels themselves are only one part of the puzzle, Mavic says. The key to the CXR80s impressively low drag figures (more on those later) is a system-based approach. Just as it pushed rim/spoke/hub system integration in the 1990’s, Mavic is now focused on the rim/tire system interface, claiming that the transition between the two and the overall shape of the system as a whole are areas ripe for significant aerodynamic improvement.
Wheels are unique in that the leading edge becomes a trailing edge as the rim rotates, and so aerodynamics needs to be addressed in both directions. Without control over the tire, only the trailing edge of the front of the wheel and the leading edge of the back of the wheel can be controlled. Mavic set out to control both leading and trailing edges at the front and back of the wheel.
To that end, Mavic split this system into three parts: first is the wheel itself, detailed above. Second is the tire, which is shaped to match the wheel profile, and third is a small rubber strip called the CX1 Blade, which fills out the remaining gap between tire and rim.
With all this in mind, Mavic developed a specific tubular tire, the Yksion CXR. It is 23mm wide — wider than one might expect out of a tire designed with a focus on aerodynamics, in fact.
The company says it could have designed around a 21mm tire and made the system a tiny bit more aerodynamic, but that sponsored teams and riders requested the 23mm size to improve cornering and comfort.
The concept, according to Mavic’s road product manager, Maxime Brunand, is to use the tire itself to create the preferred profiles, both when a specific portion of the wheel is the leading edge (front of the wheel) and trailing edge (back of the wheel).
When the tire is leading, the CXR80 rim and tire fit a NACA 0024 profile. When the rim is leading, and the tire trailing, the system fits a truncated NACA 0011 profile.
Translated into English, that means Mavic has designed the rim/tire unit to reflect known low-speed aerodynamic shapes both when air hits the front of the wheel and when it exits out the back.
Other brands — both Bontrager and Zipp, for example — sell tires ostensibly designed to perform well with their wheels. But Zipp’s Tangente uses the casing from a third-party tubular manufacturer, and most of Bontrager’s aero tire efforts have been focused on clinchers. Mavic has, as of now, the only fully integrated system.
Mavic says the tire tread itself, which alternates between short parallel lines and small dots on the shoulder of the tire, is designed to induce turbulence, helping air stay attached to the rims for longer.
The CX01 Blade, often referred to as the “link” by the Mavic marketing department, is a slender rubber strip that fills the gap between the round tire profile and the top of the brake track. The goal is a smooth transition and specific shape between tire and rim.
The strip itself is not yet approved by the UCI (thanks to Article 1.3.004, which requires any technical innovation to gain approval before use in competition), but data from Mavic suggests it is worth about 1.5 watts at 50 kph, and that the wheels are still faster than their competition even without it. We can’t see the UCI approving what is quite clearly a non-structural fairing, but that shouldn’t stop amateur racers or triathletes from using the strips, which can be easily removed and re-installed.Pages: 1 2 3 4