With a raw frame weight of 695 grams, the new Fuji SL is nearly 20 percent lighter than any bike the company has ever produced.
The new SL, which made its official debut at the ongoing Vuelta a España, is an improved version of the Fuji Altamira. Carryover highlights to the new frame include high compaction molding and RIB technology, plus new innovations such as an octagonal downtube of high-tensile strength carbon, injection-molded cable stops, and a frame with only four bonded joints. Check out this video for more details.
The cornerstone of the SL’s strength-to-weight ratio is the high compaction molding, a manufacturing technique that utilizes a series of internal molds to eliminate wrinkles and excess resin buildup in high-stress, complex radius bend areas, such as the head tube and bottom bracket . The is claimed to yield greater compaction in the carbon layers. You can see an example in the photo below, which shows a non-HC frame versus an HC frame.
Fuji introduced a limited amount of HC on the Altamira in 2013, but the SL adds the seat tube and fork crown as beneficiaries of the technology. This is designed to ensure that the interior is as smooth and finished as the exterior, which is claimed to net a lighter, stiffer, more durable frame with a livelier ride quality.
While the Altamira featured eight bonded joints, the SL uses only four; the more bonding joints you eliminate, the stronger and lighter the frame becomes because redundant material is removed and you’re utilizing carbon’s strongest properties of continuity.
The SL’s seatstays and chainstays are molded into just two, hollowed pieces, including the dropouts, which shaves grams and increases strength. These reductions play a big role in why the SL is 237 grams lighter than the Altamira.