Ascend, descend, it's all the same to these.
It used to seem that making a wheel for only one purpose was both acceptable and respectable. Climbing wheels had only one job — to minimize spokes, shallow out rims, and pump up your tire pressure beyond sane numbers, so you could muster your way up HC-grade climbs. However, today, in a world of gear ratios that play kindly to knees and climbs, riders are asking for less drag, more aero, and furthermore — wheels that transfer to smooth descents that don't leave our life flashing before our eyes as we rely on brake pads pressing against carbon through sharp corners on windy canyon descents. Zipp's tubeless 202 NSW Carbon Disc Brake Wheelset addresses both concerns by incorporating the aerodynamic features the brand built an empire on and adding the confident modulation of disc brakes. The better grip and more efficient rolling of tubeless tires also helps for climbing and descending, and the new freehub engages more quickly and freewheels with less drag. Better up, better down, better all the way around.
We'll get to all of that tech below, but it's always appropriate to start with aerodynamics (or "speed weaponry") when discussing Zipp, and the 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.
Zipp also credits ABLC with stabilizing the wheel in crosswinds, but the new generation's titanic internal width of 21mm may have a far more significant impact, stability-wise. Rim width isn't the only speed gain enjoyed by the NSW Tubeless Disc platform. Since disc brakes require no rim brake track, the ABLC dimples also extend to within millimeters of the rim bead, so the little dimples begin their work of managing airflow much sooner. The cumulative gains of all of the above feel, well, zippy. We don't have laboratory numbers to quantify this, but we've seen some industry publications run tests that do support our assertions.
And anyway, the real testing ground for a wheel like this is across limestone gravel, hardpack singletrack, and—yes—the Flemish stones. Though it inhabits the shallow end of Zipp's rim-depth pool, when we're riding the kinds of surfaces that disc brakes, wide rims, and tubeless tires are best suited for, we like fewer millimeters down there. Maybe it's because of our memories of the likes of Tommeke (or Cancellara, before he pioneered carbon-on-stones with his 2010 monument sweep on 303s) running clandestine Ambrosios on the second Sunday of April, or maybe it's because a shallower rim has more radial flex to dispel bumps and chatter. Whatever the case, we love the way it looks, the way it feels, and the way it makes us feel like a hero of the Belgian stones.
If these were any other Zipp wheels, 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.
- Tarmac to cobbles, this racing wheel dominates it all
- Update ABLC dimpling and rim shape for crosswind stability
- 32mm rim depth blends low weight and wind-cheating speed
- Generous width for plush tires of 28mm and bigger
- Disc brakes eliminate the biggest complaint we have with carbon
- Revolutionary hub replaces pawls and springs with ratchet rings and magnets
- Includes quick-release skewers with fork thru-axle adapters
- Zipp's Speed Weaponry armory equips cyclists who climb, descend, and venture onto gravel