What does a 40-ton humpback whale have in common with cutting edge wheel design? Just ask Zipp. It looked to these huge mammals to inspire the next generation of its cutting edge wheels using the science of bio-mimicry. If nature has spent billions of years solving problems why not let it influence engineering? The result is the new Zipp 454 NSW carbon clincher and a radical new design that Michael Hall, Zipp’s Director of Advanced Development, says will lead to a “total change in the dynamics of the wheel industry.”
Every Zipp wheel launch since the Firecrest shape debuted in 2010 has been about refining the new wide body shape – evolution not revolution. The Zipp 454 NSW carbon clincher is clearly not just an evolution of the Firecrest shape, it is a wholly new concept in wheel design and wears its technology on its sleeve, even if fully understanding what it does takes a PhD.
Zipp calls the new rim shape “Sawtooth” due to the undulations on its inner diameter. These undulations were inspired by the tubercles on the leading edge of a Humpback whale’s pectoral fins. But tubercles doesn’t have a sexy ring to it, so Zipp calls them HyperFoil nodes. Like the tubercles that help these 40-ton animals swim at 25 mph and turn on a dime, the Zipp 454 NSW carbon clincher’s nodes are designed to create a more stable wheel in challenging wind conditions.
It’s Zipp’s continued search for what it calls aero balance – a wheel that has both slippery aerodynamics and stable road manners in blustery conditions. At the risk of simplifying a very complex subject, the deeper a rim profile is the more aerodynamic it is, but the more susceptible it becomes to instability in crosswinds. If a wheel stays in the wheel bag because it is too difficult to handle, how fast it may be in the wind tunnel is irrelevant, hence Zipp’s pursuit of aero balance – low drag and low side force.
So the intention of the new rim shape and its HyperFoils is not to make the rim faster than the 404 in a pure aero drag sense, it is to make the speed a 58mm deep rim has more usable, for more riders in more conditions. These hyper foils are designed to increase the rim’s vortex shedding frequency. Rims that have low vortex shedding frequency create the big unstable gut churning lurches we associate with ill-handling. Side force builds up and hangs on to the rim, forcing the rider to lean into the wind to stay on line, when all that side force releases in one big dump, it feels sketchy indeed. The HyperFoils increase the frequency of that shedding, so instead of building up, it is released more frequently and in very manageable amounts, limiting its influence on your bars. When riding in still conditions the HyperFoils are essentially invisible to airflow, it’s only when crosswinds build and the wind’s yaw angle increases that they go to work. The higher the yaw, the harder they work and more effective they become. That’s the concept – at least in broad strokes. What’s really nice about this is it means a slower rider will get even more benefit. With more forward speed, faster riders see less apparent side wind or effective yaw so the HyperFoils have less work to do.
Zipp benchmarks the rim agains what it calls the ‘closest competitive product.’ Think Bontrager or ENVE, not the old fashioned 23mm wide NACA airfoil. Since the 454 seeks aero balance, not pure drag reduction, there weren’t any of the usual charts calculating seconds saved over a theoretical 40km time trial. Instead, Zipp claims a five percent reduction in side force and crosswind feedback is 15-percent lower on average across typical wind angles versus a 60mm ‘closest competitive product.’ Not huge numbers, but then the current crop of deep aero rims are getting better and better in cross winds.
Energy saved with this technology is more subjective. What is it worth to not be fighting a crosswind all day? While very significant, those type of numbers are harder to quantify. Zipp does claim that 454 now has the same handling characteristics in a crosswind as a 303, so smaller riders that felt over matched by the 404 can now ride a 454. That’s worth about 11 seconds over 40km.
The rims are now front and rear specific. Both feature a max width similar to Firecrest – 27.8mm – but now undulate between 53mm at their shallowest and 58mm deep at the peak of the nodes. Zipp tried prototypes with between eight and 120 nodes per rim. In a happy coincidence, it found that the sweet spot for these nodes was between 18 and 24 per rim, which just happens to match spoke counts. The front 454 has 18 spokes and 18 HyperFoils while the rear has 24 of each. Zipp spent four years getting to this shape with 36 prototypes and 252 hours in the wind tunnel, plus 6000 CPU hours of computational fluid dynamics and countless real world miles with wind sensing telemetry equipment to validate it all.
Zipp’s now ubiquitous dimples have also been redesigned to help the nodes do their job. Instead of covering the entire rim wall they are now in staggered sections that align with the nodes. Instead of round, each individual dimple is now a hexagon, which of course gets its own snappy name – Hexfin.
To make rims with these complex shapes was the biggest challenge ever faced by Zipp engineers huddled in their secret development lab, the Nest. Despite the increased surface area added by the undulations, the Zipp 454 NSW carbon clincher is actually lighter than the 404 NSW – 1525 grams vs 1555 grams – with similar lateral stiffness and better radial stiffness. An engineer fairly new to the Zipp team, Ruan Trouw, developed a layup for the 454 based on his aerospace background. This is the first Zipp rim to use a single-ply joint, symmetrical layup. By no longer wrapping single carbon sheets from rim wall to rim wall across the rim bed Zipp was able to eliminate any negative torque load in the structure from the carbon itself. This almost doubled the sheets of carbon needed and pushed construction time to 12 hours to make a single rim. Trouw personally trained all the personnel that are part of the 454 layup team. This is one of the reasons the NSW is the most expensive set of wheels Zipp has ever made – $4000.
As part of the NSW family the new wheels share Zipp’s other apex technologies from the Showstopper brake track to the Impress graphics. They are built around the new Cognition hub set with the magnetic free hub that cuts the friction of a traditional pawl hub in half. For now Zipp is launching just the 454 NSW as a carbon clincher, rim brake only wheel, but we expect a tubular and disc version will follow in short order. We also expect to see this new Sawtooth rim shape on deeper and shallower Zipp rims soon, its engineers assured us there is no reason the design would not be beneficial at other depths.
At first glance it would be easy to write the Sawtooth rim shape off as gimmick and some surely will, although if they do we doubt they will get this far into our report. But as we’ve seen in carbon frame design, carbon bicycle wheel development is a mature art. There is no more low hanging fruit to be picked. Improvements will be smaller and it will take big leaps to get there. Look at Trek’s IsoSpeed technology. It was written off as a gimmick back when it first launched in 2012 but has now become a staple in Trek’s line and proven its worth again and again on the race course. Perhaps Michael Hall, Zipp’s Director of Advanced Development is right and the new 454 NSW will lead to a “total change in the dynamics of the wheel industry.”
The new wheel is available right now, but there was no ride planned at the unveiling so any ride report will need to wait for another day and fully understanding what this technology offers will undoubtedly take a long term test. We’ve been riding 404’s for a decade now and the latest 404 NSW is a great wheel, already providing much of the aero balance Zipp is aiming at with the new Sawtooth rim shape. Will the new rim provide a noticeably different ride, will it be truly better? Zipp engineers are confident it will and we look forward to finding out.
454 NSW Carbon Clincher
1525g wheel set total
690g front / 835g rear
53 & 58 mm wheel depth
27.8mm max width
17mm internal width
26.4mm brake track width
18 front / 24 rear spoke count
Sapim® secure-lock nipples
Sapim® CX-Ray® spokes
MSRP: $ 4000
Retail Availability: November 2016
For more on these check out Zipp.com