Challenges racing tubulars are still made by hand, one at a time. The backstory on Challenge is that it's the recreation of the old Clement tire brand. Clement was moved out of Italy to Thailand by its parent company, Pirelli, and abandoned. The people who imported the tires in Italy, and the people who ran the factory in Thailand, then got together to provide the legendary Clement quality in a modern package. The Challenge Criterium 320 Tubular stands at the top of its current collection, providing the same quality and precision that's made it the preferred choice of professional cyclists year after year. Challenge makes its silk casings using the same machines and labor intensive processes perfected by Clement. The silk casing is still the preferred tubular material, as it's finer and more supple than either cotton or polyester. It could almost be considered 900 threads per inch TPI, but the casing is constructed differently, which means that the count isn't quite accurate. A fine silk casing is the best option for road racing because it means more of the tread contacts the ground, providing the best traction and 'feel' of the road surface. After the casing is made, Challenge glues on a belt of corespun polyester casing to the area where the tread goes. This second layer is what Challenge calls its PPS Puncture Protection System, and it's specifically made from the tightly woven polyester material in order to preserve the casing's overall supple feel. On top of that second ply is the hand glued signature Criterium tread. This proven tread pattern provides both low rolling resistance and incredible grip. Longitudinal ribs run down the center, with a herringbone structure on either side. And sticking with traditional methods, Challenge glues this legendary tread pattern by hand to the casing after the casing has been tensioned. The logic behind this is that a tread made separate from the casing rides better and with less rolling resistance because it does...