Though Challenge officially categorizes the Criterium 320 Tire as an open tubular, it is, essentially, a clincher. At least in form. In function, these tires feel more akin to tubular tires. They're supple, grippy, smart in the corners, and they ravenously devour road noise. The Criteriums aren't technically tubs, but with a ride quality that inspires modifiers like poetic, we feel it's only appropriate to grant Challenge an exception for poetic license. The Criterium's supple feel is attributable to many elements of its handmade construction, but the most important is definitely that handmade tires don't have to be vulcanized. Vulcanization is a process whereby rubber is treated with sulphur to harden it and bind the disparate materials of a tire. Since Challenge hand glues the rubber tread to the casing, the vulcanization process used in mass production is avoided altogether. The result is a buttery ride that almost makes you think you're on a tubular tire. A few other elements that contribute to the Criterium's peerless among clinchers ride include the high TPI count and the natural rubber for the tread. TPI measures the number of threads per inch in a tire's casing, with higher counts equating to a lighter tire with a suppler ride. The Criterium tops Challenge's clincher line with a TPI of 320, and the high TPI ride qualities are increased by the tire's core spun construction. Core spun means that the casing fibers are made by twisting staple cotton fibers around a central filament core, creating one yarn from multiple fibers. As a result, the material is between 40 and 50% stronger than typically spun materials without making concessions to ride quality or weight. Don't worry, we haven't forgotten about the rubber. You may not care too much that Challenge only uses locally sourced rubber for the tread, but after taking the Criteriums for a spin, you'll definitely care that they only use the natural stuff. Most tires use synthetic rubber, which is a ...