For serious cyclists, a custom-made bike promises not just a perfect fit, but a range of performance enhancements that can improve climbing, descending, sprinting, and more. Carbon fiber can facilitate these upgrades—but the material is surprisingly uncommon in bicycles from the top custom builders. Denver’s Alchemy Bicycle Company is an outlier in that regard, carving its niche with house-made tubes and joints composed of the ultralight material. The firm’s bespoke aero frames can break the sub-800-gram weight barrier and have twice earned “Best Carbon Bike” honors at the North American Handmade Bicycle Show. In addition to road models—which are also available in steel and titanium—Alchemy makes equally high-end mountain bikes.