Last night I went to an event at Sausalito’s Above Category in which Zipp Speed Weaponry presented a new wheel, called the 454. Well, not just a new wheel, but a new generation of wheel. It represents as big a departure from existing technology and know-how as Firecrest did when it was first introduced more than five years ago.
What makes this rim different is easily apparent to the eye. The sawtooth shape is another expression of Zipp’s pursuit of improved boundary-layer aerodynamics. Firecrest, and it’s rounded spoke bed was undertaken for two reasons, to make the wheel fast and to handle better. The handling piece was a matter of low-frequency vortex shedding. That’s the buffeting you feel when you ride a deep-section wheel in a crosswind. Those dimples that dot Zipp rims—they’re termed ABLC for Advanced Boundary Layer Control—create a microturbulence at the surface of the rim so that the wind attaches and stays attached until it releases more gently than it would were the surface smooth. This new sawtooth shape performs the same sort of function; in creating turbulence at the spoke bed, the passing airflow attaches better and releases better.
The shape came about from Zipp’s study of natural structures with similar functions. The structure they noted most earnestly were the tubercles at the end up humpback whale fins that allow a beast bigger than a school bus to turn like a Mini Cooper. This field of inquiry is termed biomimicry, and Zipp pursued a number of sources of inspiration. That these shapes are a recurring theme in nature should be some indication of the idea’s validity.
To give you some idea of Zipp’s dedication to this pursuit, they produced 36 different rim prototypes. There were more than 6000 hours of CPU time in CFD testing, a volume I’ve never encountered in the bike industry. Consider that often how CFD testing is doing is that an engineer will often set up a test at the end of the work day and then head home. If they’re lucky, that test will be complete when they return to work the next day. On average, that’s 12-ish hours of testing per day. Real world wind-tunnel testing was similarly gargantuan, with a whopping 252 hours spent in the wind tunnel.
The sawtooth shape results in a rim that varies between 53 and 58mm of depth. The node, or bump that helps give the rim its sawtooth shape is called Hyperfoil; it’s this shape that increases the frequency of the vortex shedding so that in crosswinds a deep-section wheel can feel like a box rim.
The ABLC dimples have changed shape—yet again—and are now hexagonal, a development they are calling Hexfin.
For the record, I have not had the opportunity to ride the 454 wheels, yet. And I’m presenting their claims to you with some explanation but no jaundiced suspicion. Why? My experience with Zipp’s work has been that with each new generation of Zipp wheels they have met their claims. I’ve never melted one of their carbon clinchers, and they continue to be the best-braking carbon clincher on the market—Zipp even asserts that it’s Showstopper brake surface stops better than an aluminum rim, when paired with their Tangente brake pads; I can at least report satisfying braking. When it comes to deep-section carbon wheels in windy circumstances, especially gusty ones, only Enve rivals Zipp for the handling title. Without Enve as a competitor, Zipp would be peerless for carbon wheel performance.
These wheels are the most challenging to produce Zipp has ever offered. Each rim requires 12 hours of hand labor to produce, and all the rims are made, and wheels built, in Zipp’s facility in Speedway, Indiana.
Zipp uses Sapim CX-Ray spokes for their builds, 18 front and 24 rear. The front wheel weighs in at 690 grams front and 835g rear, for a total of 1525 for the wheelset. The rim has a 17mm internal width and a 27.8mm maximum outer width; it’s optimized for 25mm tires, and for the time being, this is a clincher-only wheel.
There’s a bottom line, performance-wise. The 454 is reported to be faster than Zipp’s 404 NSW wheels, while offering the handling of their 303 NSW wheels. It’s an intriguing assertion and one I’m eager to put to test.
Of course, all this engineering and technology comes at a price. For anyone whose frugal sensibilities are easily disturbed, just hit the back button now. For the rest of you, the take-home price is $4000 for a set, though front and rear wheels will be available individually.
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