The latest version of Zipp's 404 Firecrest Carbon Tubular Road Wheel features a few big changes that further improve the rims' structural integrity. Given that the previous design was already proven on the most punishing courses in cycling (think stones), the changes are welcome even if they're unnecessary. The dimpling of Advanced Boundary Layer Control (ABLC) also sees some changes, returning with a higher count and a redesigned dispersion pattern.
Along with the rims' signature bulge, ABLC also helps improve stability at common cycling yaw angles by directing side forces more toward the steering axis. We definitely appreciate ABLC — if for no other reason than that it's become a staple in the peloton, winning races under names ranging from Cancellara to Armistead — but we're actually a bit more juiced about the Visco-Elastic Constrained Layer Control (VCLC) and Carbon Bridge technologies that Zipp is rolling out.
VCLC is similar to a construction model that we're seeing more and more in high-end frame manufacturing, especially among the venerable Italian names. It involves, to deconstruct Zipp's initialism, constraining a visco-elastic layer between the wheels' carbon fiber layers in order to increase the structure's ability to absorb and control road noise. As mentioned above, we're used to seeing this in racing frames, but Zipp may be the only manufacturer to bring it to wheels.
The Carbon Bridge design incorporates Kevlar threads in the carbon layup to take advantage of Kevlar's 350% greater resistance to impact. The benefits throughout the wheel are obvious, but higher durability is especially welcome at the tire mounting surface, which is often the first area to take a hit, and Zipp claims that the 404's durability under duress jumps by just over 40%. Zipp even goes so far as to make the joke that the wheels are practically bulletproof.
The rims are anchored by Zipp's new 77 and 177 hubs in the front and back, respectively. The new hub model features a flange and spoke lace design meant to decrease the torsional twist a wheel can experience under hard accelerations and the lateral flex produced by long periods of steady, uphill grinding.