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by James Huang
October 25, 2016
Photography by James Huang
TECH NEWS BROUGHT TO YOU BY BIKEEXCHANGE
The “nest” is Zipp’s nickname for where its most advanced development work occurs — a wholly separate part of the company’s facility in Indianapolis, Indiana, with limited employee access, no windows, and a permanently locked door that requires special keycard access. It is in this room that Zipp conceived its latest 404 NSW carbon clinchers, and it’s indeed one hell of a wheelset, with an innovative hub, industry-leading aerodynamic performance, and astoundingly good braking performance. As promised, the 404 NSW (Nest Speed Weaponry) is one of the very best aero wheelsets money can buy, but does that justify its extravagant cost? Read on.
As one of Zipp’s flagship products, it’s no surprise to find that the 404 NSW carbon clinchers are packed with every bit of technology available in the company’s toolbox.
The 404 NSW’s 58mm-deep carbon rim uses Zipp’s latest “Firestrike” profile, with an extremely fat and blunted shape that measures 26.4mm-wide at the brake track and a bulbous 27.8mm about halfway down the rim — in fact, it’s so wide that prospective buyers should double-check compatibility with their frame and brake calipers first. According to Zipp, this shape not only makes for a more aerodynamically efficient wheel at a wide range of wind angles, but one that’s also more manageable in blustery conditions.
Zipp’s latest “Firestrike” rim profile is extremely fat and blunt. Recommended tire size is no wider than 25mm. Photo: Zipp.
Zipp has long championed its rims’ golf ball-like surface texturing. According to Zipp, these create a small boundary layer of turbulent air on the surface of the rim, which the company says helps passing air “stick” to the rim for smoother overall flow, especially off the trailing edges of the rim-tire profile. That concept has evolved further still with something Zipp calls ABLC (Aerodynamic Boundary Layer Control) SawTooth, a specific circular saw blade-like dimpling pattern that Zipp claims makes the 404 NSW even faster and more stable than its predecessors.
“Our new Sawtooth dimple design consists of 12 nodes that are precisely clocked to start aerodynamic shearing at a rate of 50Hz at a rider speed of 20mph,” says Zipp’s marketing collateral. “Sawtooth accomplishes this by inducing small sheet vortices that shed at a low magnitude, but at a higher natural frequency, thus decreasing the laminar bubble effect on the aerodynamically shielded side of the rim’s profile to further reduce high yaw drag and improve crosswind stability.”
It’s no surprise to see a Zipp flagship carbon wheel with a dimpled surface. However, this latest iteration — called ABLC SawTooth — arranges those dimples in a toothed pattern that Zipp claims reduces drag and improves handling stability even more than before.
Thankfully, the technology incorporated into the made-in-Portugal Cognition hubs is a little easier to grasp.
Zipp’s Axial Clutch freehub design uses a pair of toothed drive rings instead of a conventional ratchet-and-pawl setup — not entirely unlike DT Swiss’s long-running Star Ratchet arrangement.
However, whereas DT Swiss uses two conventional steel springs to push the ratchet rings together, Zipp relies on a trio of small magnets. Zipp also likes to point out that its Axial Clutch design “disengages the ratchet mechanism” when the rider is coasting, which, in theory, results in lower friction and quieter running.
“Low-drag coasting via Axial Clutch means you can pedal less when riding through rolling hills or drafting in a headwind, achieve higher speeds when coasting in an aero tuck, or opt to stop pedaling a moment sooner before entering a corner — and bank that wattage for exiting the corner.”
The Cognition hub set looks trick, and the rear one hides a novel driver mechanism.
Those friction claims seem intuitively reasonable, but it’s perhaps worth noting that Zipp uncharacteristically offers no lab figures to reinforce them — nor is there a ceramic upgrade over the standard Swiss-made ABEC 5 stainless steel cartridge bearings. Nevertheless, the stealthy aspect may appeal to racers, and the mechanism’s ten-degree engagement speed is relatively quick and responsive for a road hub. Special hub shell shapes supposedly yield more consistent bearing preloads, too, with no adjustments needed.
Zipp joins this all together with Sapim CX-Ray bladed stainless steel spokes and externally situated Sapim Secure-Lock alloy nipples, using two-cross 24-hole rear and radial 18-hole front lacing patterns.
Lest you think Zipp has only targeted flatland speed for the 404 NSW carbon clinchers, keep in mind that they’re also quite light for something this deep. Actual weight for the set without rim tape is 1,585g (733g front; 852g rear; plus 65g for the included Zipp Tangente titanium-shafted quick-release skewers) — 30g heavier than claimed, but well within reasonable expectations for manufacturing tolerances.
Zipp has always been thorough with its aerodynamic work, but it has also been at the forefront in terms of improving the braking performance of its carbon rims. Previously, much of that work has focused on improving the rims’ structural integrity at the high operating temperatures that can often be produced from prolonged braking in mountainous regions. With the new 404 NSW, though, it’s all about stronger braking in general.
The new “Showstopper” sidewalls feature a lightly roughened surface for increased pad-rim friction in dry conditions, but also molded-in grooves to lend an extra measure of mechanical grip between the rim and brake pads. Those arc-shaped channels are meant to help evacuate water for more predictable stopping in the wet, too, not unlike how grooved tires are supposed to do the same for traction in Formula 1 cars.
The “Showstopper” sidewalls feature a roughened surface, embedded silicon carbide ceramic particles, and molded-in grooves that are designed to boost both dry- and wet-conditions braking performance.
Meanwhile, that entire area is littered with silicon carbide ceramic particles embedded within the high-temperature resin matrix. Zipp doesn’t include these to increase stopping power, though, instead using the material to boost long-term durability. After all, carbon brake tracks eventually wear out, just like aluminum ones do, but with a much higher replacement cost so it’s nice to see some attention paid in that department.
Zipp includes its own Tangente pads (for use with Shimano/SRAM holders) for use with the 404 NSW wheels, which are made by SwissStop to its own specifications.
The ultimate purpose of any aero wheelset is to be more, well, aero. However, we didn’t conduct any independent wind-tunnel testing of the new Zipp 404 NSW carbon clinchers to verify the company’s drag claims, and any Chung methods of aero testing on open roads would only have told us how well they did for one particular bike and rider.
That said, Zipp’s flagship wheels have generally been at least among the best available in terms of aerodynamic performance, and based on my several months of test rides here in Boulder, Colorado, I have little reason to dispute the claims. Truth be told, most top-end aero wheelsets are within spitting distance of each other in terms of drag, so it makes more sense to concentrate on other performance traits that better set each option apart, such as crosswind stability, stiffness, and braking performance — and it’s here where the 404 NSWs mostly shine.
Colorado’s Front Range area is notorious for violent winds that sweep down out of the Rocky Mountains and onto the flatter plains to the east. Coincidentally, this foothills area is precisely where Boulder is situated, which makes it an ideal place to test the crosswind behavior of aero wheels.
The maximum 28.5mm width of the 404 NSW profile actually falls roughly halfway down the side of the rim.
In general, I’d characterize the 404 NSW’s handling behavior in crosswinds to be noticeably better than most other wheels of this depth, but not quite the bastion of stability Zipp’s marketing might have you believe. Make no mistake — as good as it is, this is still a deeper-section wheel that requires attention when the winds start to blow. Mild and steady breezes required just a slight windward lean to stay on the straight-and-narrow, and sudden gusts were mostly easy to correct provided they weren’t too severe. High-speed descents in swirling conditions were slightly unnerving, though, with an occasional light-feeling front end.
Riders who rarely have to deal with such conditions likely won’t find much of an issue at all with the 404 NSW’s stability, but others might want to consider downsizing to a shallower 303 NSW up front instead. I’ve spent plenty of time on Enve’s differential-profile SES 4.5 aero wheelset, for example, and have generally found that sort of staggered setup easier to manage overall.
I’ve nothing but praise for the 404 NSW’s braking performance, however, which is remarkably good in dry conditions — far better than any other full-carbon rim I’ve used over the years, and even better than many aluminum rims I’ve used, in fact. When paired with the included Tangente pads, initial bite is confidently strong and immediate, with minimal hand effort required, a predictable and linear build in power all the way to lock-up, and only a bit of squealing when very hot.
The 404 NSW wheels feature printed-on graphics, a process that Zipp says allows the surface dimples to better perform their intended job. It looks neater, too.
Wet-weather braking is somewhat better than usual, too, although that’s not saying much given the low bar set by most carbon rims. The 404 NSW’s molded-in grooves seem to help evacuate water as intended, but it still can’t match an average aluminum rim.
The rims’ fat profile and the wide spoke-bracing angles also make for outstanding side-to-side stiffness — so much so that I found it noticeable on especially fast and tight downhill corners, where lesser wheels would sometimes start to fold a bit under the loads applied. Brake pad rub was nonexistent, too, even when sprinting and climbing out of the saddle.
As the best wheels often do, the 404 NSW even manage to feel lighter than its numbers would suggest with a lively feel when you apply the power. Although I can’t say for certain, credit likely goes to the stout two-cross lacing pattern out back along with the large effective spoke flange diameters.
As for the Cognition rear hub, its Axial Clutch mechanism is unquestionably neat, but I can’t say I noticed any performance benefit on the road. I should also point out that while the system is very hushed while coasting, it is not completely silent. Moreover, a thorough tear-down of the mechanism reveals that there isn’t actually any sort of device built into the system to pull the ratchet rings apart when you aren’t pedaling, despite what the company’s marketing materials suggest. The ramped teeth still slide against each other, just as they do on a Star Ratchet-equipped DT Swiss rear hub, but the Axial Clutch’s magnets seem to exert a lower spring force than the steel springs used by DT Swiss so the “click” isn’t as pronounced.
The Cognition rear hub’s Axial Clutch driver mechanism looks unusual, but in essence is very similar to DT Swiss’s long-running Star Ratchet design, only with magnets in lieu of conventional steel springs. Freehubs are interchangeable between SRAM/Shimano 11spd, Campagnolo 11spd, and SRAM XD standards.
The Axial Clutch perhaps isn’t quite everything Zipp makes it out to be, but that doesn’t give it as much credit as it perhaps deserves. The metal injection molded mechanism is incredibly thin, and its larger diameter allows the driveside hub shell bearing to be pushed further outboard than usual.
At its essence, Zipp’s Axial Clutch driver is very similar to DT Swiss’s Star Ratchet mechanism with two opposing steel ratchet rings — one anchored in the hub shell, and the other in the freehub body. The difference here, though, is that only one ring has ramped teeth; the other one is flat, but with cutouts into which those teeth engage.
Three magnets pull the ratchet rings against each other, similar to what steel springs would do in a conventional hub.
I can’t help but wonder how well that lower spring force will play out over time as a result. Whereas current DT Swiss hubs use two springs to push the ratchet rings together, earlier examples — dating all the way back to the Hügi days — used just one. At least in those hubs, the lower spring force was sometimes problematic under higher pedal loads, or if there was insufficient lubrication inside the hub shell to keep the ratchets from sliding axially as they should. Zipp also hasn’t exactly has the best track record when it comes to long-term hub durability, but time will tell with this all-new Cognition design.
In any event, Zipp continues to be at the head of the pack in terms of aerodynamics, but is still frustratingly slow to adopt some of the latest (positive) performance trends. Zipp only just introduced the 404 NSW a few months ago, and yet the internal rim width is only a modest 17.25mm — 2-4mm narrower than more progressive options such as from HED, Bontrager, and even Roval. As a result, the Zipps don’t offer quite the same boost in cornering grip, ride quality, and drive traction, nor do they allow for as much flexibility in terms of inflation pressure without adversely affecting performance.
The traditional tire bed profile doesn’t allow tires to be run tubeless, either — hardly a dealbreaker, but a bummer that the option isn’t at least offered. And as much as I feel like I’m beating the proverbial dead horse about complaining about this issue for so many years, I’m still continually disappointed to see external-cam quick-release skewers. The brass cam carriers used here admittedly operate with much less friction than the nylon ones normally found on these things, but they still don’t work as well as good internal-cam skewers, which consistently produce more clamping force for a given amount of hand effort.
Zipp’s new 404 NSW wheels are the company’s most advanced carbon clinchers to date.
NSW, or Nest Speed Weaponry, is a reference to Zipp’s advanced development lab, affectionately referred to as “The Nest.”
Because of the dimpling pattern and the shape of the sidewall grooves, the rims are marked with a directional arrow.
The aluminum spoke nipples will require extra care over the long haul, but they’re externally located for far easier servicing than if they were hidden away inside the rim.
Each set of Zipp 404 NSW wheels comes with special brake pads, titanium skewers, and valve extenders made for Zipp by Silca. The silicone rubber coating seems like a minor detail, but it keeps the valve from rattling without the need for any supplemental tape.
The star-shaped flanges supposedly reduce the outward stress on a hub shell that can adversely affect bearing preload. Whereas spoke tension normally tries to expand a hub shell outward (thus affecting the bearing bore size), each pair of spokes effectively cancels out the opposing tensions — or so goes the theory.
The scalloped ends on the Cognition front hub are said to help offset the outward stresses created by spoke tension for more predictable and consistent bearing bores. Unlike some older Zipp hubs, these aren’t adjustable for preload (nor is any adjustment needed, according to Zipp).
The Cognition front hub uses a notably sleeker shape.
The included quick-release skewers look sharp, and work reasonably well. They’d work even better with lower-friction internal cams, though.
Doh! The silicone rubber covers on the included valve extenders help keep the valves from rattling, but they’re apparently not terribly durable.