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“Steel is real”, the saying goes. And the retort is always “Real heavy.”

Some of us at Above Category have been all-too familiar with the saying. We love good steel’s subtle aesthetic and lively ride quality, but when it comes to racing at a professional level, it’s usually tossed by the wayside in favor of lighter, snappier carbon offerings. Enter the Mosaic RS-1, the Boulder, Colorado-based framebuilder’s top-end steel offering. And while Mosaic’s highest end steel is indeed real, it’s also light. So light, in fact, that many RS-1s we assemble in the Above Category Skunkworks with relatively “conventional” groupsets end up healthily below the UCI’s 15lb weight limit. Built from one of the lightest ferrous tubesets available, TrueTemper S3, the RS-1 shaves weight with a standard-diameter headtube, a TIG-welded front triangle, and a svelte ENVE 1.0 fork as stock equipment. All of the weight savings hasn’t sacrificed ride quality, with flex from the front-end almost undetectable on even the most technical high-speed descents and all-out sprints.

The RS-1 is the steel bike for the carbon aficionado, for the racer looking to stand out from the crowd, and for the rider looking for the classic ride of steel in a mass palatable to even the biggest of gram-counters. We’re happy to report that we’re all three at different times, and the RS-1 remains one of our favorite bikes. The RS-1 meets the same level of methodical quality and attention to detail that Mosaic is famous for as a standout American builder, with a litany of paint options, finishes, and add-ons available like fender mounts, disc mounts, pump pegs, and brazed-on seatclamps.

Every Mosaic RS-1 that leaves Above Category is custom-built for the individual, with geometry based on your answers to our questions about your riding style, current bike setup, riding/racing aspirations, and biomechanical dimensions. Due to the S3 tubing’s small diameter and thin-wall drawing, we offer the RS-1 in external mechanical shift routing or SRAM eTAP compatibility only, with internal brake routing through the top tube standard equipment.