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It’s not often that cycling industry engineers cite whales as the inspiration for their designs, but the stepped leading edge on the pectoral fins of humpback whales served as the biomimetic model for Zipp’s latest 454 NSW rim shape, which the company claims reduces aerodynamic drag and improves stability in gusty conditions.
To be clear, I like whales. They’re awe-inspiring, giant mysteries of the sea. Males sing long opuses in the hopes a female might be listening. Groups of whales blow circular “bubble nets” to corral their prey. They spectacularly propel their massive bodies out of the water for reasons no one fully understands. But do whale fins truly inspire better wheel designs? As usual, Zipp has the numbers to support its argument, but the on-road experience isn’t quite as clear.
Gliding through the water, slicing through the air
High-performance submarines and airplanes have smooth leading edges on their various wings and control surfaces. The designs have been refined over hundreds of years, the result of countless hours of engineering, research, and development. Many long nights at the whiteboard, fueled by lots of coffee.
Despite that hard work, Mother Nature had a significant head start — millions of years, in fact — and the idea behind the burgeoning field of biomimicry is that those natural structures exist for very good reason. In contrast to man-made machines, a humpback whale’s pectoral fin is anything but smooth, its leading and trailing edges riddled with distinct bumps called tubercles. As it turns out, scientists have discovered that those tubercles locally vary the pectoral fins’ stall angle, allowing the whale to maneuver in much tighter circles than it would otherwise be able with smooth-edged appendages.
Tubercles are only now finding their way into bicycle components, but the design has been utilized in other industries. Engineers have been testing tubercle-equipped wind turbines for over a decade now to improve their power generating efficiency at varying wind angles. Industrial ventilation fans with saw-like leading edges are said to move more air at lower rotating speeds. And even computer fans are supposedly better able to keep internal components cool, while running quieter, when fitted with new-school blade shapes rather than traditional ones.
In fact, the business model of Canadian intellectual property company WhalePower, founded in 2005, is entirely predicated on the way bumpy leading edges improve the efficiency of rotating turbines and turbine-like devices.
It seems only a matter of time before those smooth leading edges on airplanes and submarines aren’t so smooth.
In the case of the new, fancy-looking 454 NSWs, Zipp says the so-called SawTooth stepped rim shape reduces the wheels’ aerodynamic drag by smoothing out the flow of air as it passes across the leading and trailing edges. There’s also the claimed side benefit of improving stability in crosswinds, since that staggered shape supposedly reduces the turbulence that is normally responsible for knocking a rider off-line in blustery conditions.
Zipp taps Mother Nature for yet another feature of the 454 NSW’s molded carbon fiber rim, too: the latest HexFin ABLC dimpling pattern supposedly draws its inspiration from shark skin, further reducing surface drag as compared to Zipp’s older golf ball-like texturing.
For the 454 NSW, Zipp bundles all of that natural inspiration into an alternating-depth (53-58 mm) carbon clincher with an internal width of 17 mm, and an ultra-fat maximum external width of 27.8 mm. Those rims are connected with Sapim CX-Ray bladed stainless steel spokes (18 front, 24 rear) to Zipp’s own Cognition hubset, which features a magnetically actuated driver mechanism in the rear wheel — meaning the freehub uses magnets, rather than steel springs, to push the drive rings together.
Claimed weight is 690 g for the front wheel, and 835 g for the rear. I measured my set at 680 g and 829 g, respectively, without rim strips. The included titanium-shafted quick-release skewers add another 70 g.
As for the retail price, perhaps you should sit down. Officially figures for the Zipp 454 NSW rim-brake carbon clincher wheels are US$4,000 / AU$6,100 / £3,500 / €4,000, but hey, at least you get two. A disc-compatible option has recently been added, too, and although there currently is no tubular compatibility on tap, it’d be reasonable to expect Zipp to release one in the near future.
Flying fins, or beached whales?
Having recently tested Zipp’s more conventionally shaped 404 NSW, I’ll say this straight away: while the 454 NSW wheels certainly felt fast on the road, I couldn’t detect any advantage from the saddle in terms of straight-line speed. That said, aerodynamic efficiency is a notoriously misleading thing to qualify subjectively — especially at this very pointy end of the performance spectrum — and even Zipp admits that the two wheelsets are virtually identical in terms of aerodynamic drag at most yaw angles. If anything, I apparently should have been alarmed had I felt that these were tangibly quicker.
Given that, then, what justifies the 454 NSW’s substantial price premium? In this case, it’s not about flat-out speed, but rather stability. Specifically, Zipp claims the 454 NSW’s tooth-like rim profile and unusual dimpling pattern yields a 15% reduction in “crosswind feedback” across nearly all typical yaw angles relative to the normal-looking 404 and 404 NSW rim shape (when installed on a bike, and with a rider on board). Moreover, Zipp says the way the 454 NSW reacts in crosswinds is more predictable for safer riding overall.
“The 454 rim results in a more predictable ride experience due to controlled vortex shedding,” said Zipp PR content manager Dan Lee. “This occurs at a higher and a more defined shedding frequency compared to the competitive product in the class due to the Hyperfoil nodes and HexFin Dimples.”
My usual route for testing the stability of deeper-section road wheels includes a fast and twisty downhill that rockets back into Boulder down from the surrounding foothills. Although the winds aren’t necessarily as persistent there as they are on the main drag heading north out of town, they’re consistently inconsistent: calm through one section, blowing suddenly from the left in another, then strong from the right a few seconds further down the road. Between the high speeds and multiple corners (several of which are slightly off-camber), it’s long been my go-to crucible for wheel stability.
So how did the 454 NSW fare?
Despite what Zipp has likely measured in both wind tunnel tests and computer simulations, I couldn’t tell much of an difference out on the open road between the 454 NSW and 404 NSW after multiple trials through my test segment. Take that with a grain of salt, though: a 15% difference isn’t exactly tremendous, and such subtleties are virtually impossible to distinguish without the benefit of reliably repeatable conditions. Nevertheless, according to Lee, “most riders we’ve talked with do notice the stability of the 454 NSW compared with the 404,” and at least one owner I spoke with says he can feel a tangible difference as well. Still, given how much emphasis Zipp places on the 454 NSW’s supposedly superior stability as compared to a more conventional rim shape, I had hoped for more.
It’s not just about stability
The claimed aerodynamic improvements of Zipp’s latest road wheelset may have been lost on this particular rider, but that’s not to say that the 454 NSW isn’t still noteworthy.
The textured and silicon carbide-infused Showstopper sidewalls continue to impress me with their fantastic dry-conditions performance. Initial grip is strong and positive when using the supplied Zipp Tangente Platinum Pro pads, and power ramps up in a predictably linear fashion as you squeeze the lever closer to the bar. The molded-in pattern generates more noise than an aluminum rim, but it’s not ear-piercing or annoying. Wet-weather braking is very good, although that’s relative; I still find the latest crop of textured and/or ceramic-coated aluminum rims to provide superior performance in that respect.
Either way, pad wear is noticeably accelerated (with more brake dust to match), although any rider with sufficient cash to drop on these wheels isn’t likely to fret too much about having to buy pads more frequently. According to Lee, riders on Showstopper-equipped wheels should expect to burn through two sets of pads per season on average. Based on my experience here in mountainous Colorado, I would expect that number to be substantially higher.
Regardless, it’s a comparatively small price to pay for such fantastic braking performance on a carbon rim, and Zipp’s latest models generally have superb reliability records for withstanding the high heat of prolonged braking.
Zipp has a decidedly spottier history for hub reliability, but the company might finally be shedding that reputation for good with the flagship Cognition hubs. Nearly two years have passed since they were first introduced in early 2016, and I could find nary a single failure on any of the popular online forums where Zipp’s earlier hubs have been ruthlessly bashed. That’s particularly impressive given the rear hub’s fancy AxialClutch magnetic driver mechanism.
As compared to the conventional pawl setup Zipp has used in the past (and still uses on lower-end models), AxialClutch features a pair of steel multi-tooth drive plates, whose splined housings spread the pedaling load over a much larger area than standard pawls. In concept, it’s not entirely unlike what DT Swiss uses in its bulletproof Star Ratchet driver design.
Zipp engineers have also cleverly taken advantage of magnets’ digressive force curves (meaning their attractive force greatly diminishes with increasing distance). The plates don’t completely disengage while coasting, but the teeth skim across each other so lightly that there’s a noticeable decrease in drag. The ratchet is pleasantly quick to react for a road hub, too, requiring no more than ten degrees of freehub body rotation before the driver mechanism re-engages after coasting.
“We use attracting magnets instead of mechanical springs,” Lee explained. “The resulting force is highest when the ratchets are fully engaged and drops exponentially when the ratchets are separated. At high coasting speeds, the ratchets are sliding fast enough to not fully engage. The axial engagement movement gets near zero and the ratchets are almost not touching each other.
“We use the hole pattern of our ratchets to create an oscillating magnet force,” he continued. “Basically, the magnet is switched on and off 36 times per revolution. This effect assures sufficient attraction force when it is needed and still helps to keep the ratchets sliding smoothly at high speeds.”
Be that as it may, it’s unfortunate that Zipp couldn’t produce a more pleasing soundtrack to accompany that fancy magnetic choreography. AxialClutch seems to work as intended — and so far, it also seems pretty reliable — but it sounds tinny when coasting at higher speeds. Zipp doesn’t provide official recommended service intervals, but according to Lee, the company is typically seeing riders log about 1,000 hours of use before the driver starts sounding raspy – the telltale sign that service is required. Zipp is very specific about both the type and amount of oil (not grease) to be used. Curiously, Zipp also recommends that if a freehub body bearing becomes worn or damaged, the entire freehub body assembly should be replaced, not repaired.
Otherwise, the wheels are admirably rigid when sprinting and climbing out of the saddle, and rock-solid under hard cornering loads; brake pad rub isn’t an issue. Zipp’s recent push toward tubeless compatibility unfortunately came after the introduction of the 454 NSW, though, and conversions aren’t recommended. Internal width is pegged at a modest 17 mm, too, which is a couple of (significant) millimeters narrower than more progressive shapes from HED, Reynolds, and others.