If you're like many of us, you may not be a fan of the mismatched rim depths that many other cyclists prefer. It's not necessarily an act of judgment, just a question of preference. To simplify things for those who like matching rim depths, we're offering Zipp's tubular 404 Firecrest Carbon Road Wheelset. This represents a slight departure from the usual option of buying front and rear Zipp wheels separately; the wheels themselves help you depart in haste in a race's finale.
As with any deep Zipp wheel, the 404 Firecrest's side-wall bulge and Advanced Boundary Layer Control (ABLC) dimpling are its signature features, both of which contribute to improved stability at the kind of yaw angles you'll actually experience on the road, not while cloistered in a wind tunnel. The ABLC is especially important in the latest generation of Firecrests, as the number and distribution have been revisited to net even more aerodynamic advantage. While these two features tend to steal the headlines, Zipp's Visco-Elastic Constrained Layer Control (VCLC) and Carbon Bridge technologies may be even more impressive despite being less evident from a visual standpoint.
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. To unpack Zipp's initialism, VCLC involves constraining a visco-elastic layer between the wheels' carbon and resin 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 while you're slowing to dismount and stare in frustration at your beautiful — but now useless — tub. Zipp claims that the introduction of Kevlar boosts the 404's durability under duress by just over 40%.
As with all new generation Firecrests, the 404s are anchored by Zipp's 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 and lateral flex produced by hard accelerations, sprinting, and punchy climbing.