So much more.
Making a climbing wheel used to be simple. All that mattered was reducing spoke count, milling the hell out of the shallowest, narrowest rim possible, and pumping your sub-23mm tires up to 140psi. Zipp's 202 NSW Carbon Clincher Wheelset is indicative of how much the industry approach to climbing wheels has changed. It privileges aerodynamics as much as reducing circumference mass because we now know that—even on climbs—drag is as much of an impediment as the inertial resistance of rim weight. Through the application of Zipp's aerodynamic shaping and texturing, the 202 NSW actually aids climbing so much more than the lightweight climbing hoops of old because it's, well, so much more than the lightweight climbing hoops of old.
We're always excited about free speed gains, but we're actually a little more stoked about the improved braking. The rims are equipped with an updated version of Zipp's Showstopper brake track, which enjoyed an impressive debut on the Firestrike 404 but has already been improved for the NSW line of wheels. It's still imbued with the same silicon carbide particles, which increase the bite into the brake pads for increased modulation and control in wet conditions, but the brake track's direction-specific grooves have increased in number and changed in depth. The tweaked grooves are credited with even more improvements in braking, and—though Zipp doesn't specifically make this assertion—it does stand to reason that the grooves clear intervening material and help keep the pads on the rims where the silicon carbide can get a hold of them.
The original Showstopper netted some pretty impressive stopping across all conditions, but Zipp assures us that the new version is even better. The upshot is you can hold speed longer while approaching a corner, braking later and gaining tiny increments of time with each bend or switchback, helping you protect the gains you made during the climb by preserving your advantage on the descent. You can also feel that much more confident is avoiding darting canines, distracted motorists, and unexpected road debris.
In addition to the brake track, Zipp's signature Aerodynamic Boundary Layer Control (ABLC) dimpling returns with a new designation. It's called SawTooth Technology, and it consists of ABLC dimples applied in a single pattern repeated in 12 discrete swathes (or "nodes") across the rim's surface, looking much like the strokes of a paint brush. Zipp claims that SawTooth reduces side wind forces by "reducing the laminar bubble effect on the aerodynamically shielded side of the rim's profile." Translated into less technical terms, that means the rim's dimpling is designed to dispel the negative, drag-inducing force on the rim's non-wind side.
SawTooth's premise stems from 42 computational fluid dynamics studies and testing that spilled out of the wind tunnel onto—gasp!—actual roads. In actual wind. You know, the conditions that we actual cyclists face every time we throw a leg over the top tube either side of trainer season. To help understand how SawTooth works, consider an aerodynamic NACA shape in the pristine wind tunnel conditions of zero-degrees yaw. When air resistance is perfectly head-on, drag only exists in a parallel plane with an object, so a teardrop NACA cross section reduces drag to its absolute minimum by reducing the wake. Turn the yaw angle upwards of 15 or 20 degrees, though, and a true NACA shape begins to experience drag from the side opposite cross wind pressure as well. This lateral drag is Zipp's "laminar bubble," and it's the phenomenon responsible for the violent instability that leaves us wrestling with our bikes on gusty days.
Though Zipp was one of the shape's early adopters, the industry is now replete with rounded, bullet-shaped rim designs that aim to lessen destabilizing drag from cross wind forces; however, if Zipp's numbers are any indication, the SawTooth nodes take that reduction to a whole new level by better controlling cross winds as they detach from the rim's opposite face. Essentially, the NSW rim shape and SawTooth Technology contribute to a ride that requires less correction in windy conditions, and the corrections themselves are more subtle and intuitive than with yesterday's NACA profiles.
If this were any other Zipp wheel, that would be the end of the show; however, the new Cognition rear hub is every bit as innovative as the wheelset's rims. The hub is centered on Zipp's Axial Clutch mechanism, which features two Metal Injection Molding (MIM) ratcheting rings—one mated to the freehub body and one mated to the hub body. The two rings are machined like a ratchet, so they ramp off of each other while freewheeling but engage each other during pedal input.
Compared to a standard pawl design, which actually resembles a drum brake, the Axial Clutch's MIM rings engage laterally to reduce friction while freewheeling, so coasting doesn't negate watts already spent. We're familiar with this model, as we've seen similar mechanisms on the designer hubs featured in top-end custom builds for years now, but Zipp is the first to replace the usual tensioning agent, steel springs, with magnets. This substitution further reduces friction between the ratcheting rings, making for what may be the smoothest freewheel on any mass-produced hub set. It's a design that we suspect will eventually be the norm, and Zipp is leading the charge.
- Lightweight wheels that shrug off gravity and drag alike
- Update ABLC dimpling and rim shape for crosswind stability
- 32mm rim depth blends light weight and wind-cheating speed
- New brake track for I-can't-believe-it's-not-alloy stopping power
- Hub replaces pawls and springs with ratchet rings and magnets
- Zipp flexes its R&D muscles with improved braking, freehub engagement, and—of course—aerodynamics