Zipp 404 NSW

I reach for these wheels more than any other set in the vast VeloNews stable just on instinct: The 404 NSW wheels are stiff, do-it-all hoops with a wide footprint for better traction and rolling resistance. But Zipp’s venerable 404 Firecrests cost $1,000 less, so the question is, are the NSWs a grand better?

For the top-level racer, yes. For the rest of us, perhaps not.

One of the most important differences between the Firecrests and NSW is the Cognition hubset, an upgrade that promises near-instant freehub engagement thanks to its Axial Clutch system. Instead of relying on springs to engage and disengage the freehub, the Axial Clutch relies on magnets that pull a ratchet ring away from the engagement ring. When you pedal, the rings engage; when you coast, they disengage quickly and slide smoothly over each other. Zipp says this system allows quicker engagement and lower resistance when coasting.

At first we found the engagement to be about as good as it is on Firecrests. There seemed to be a little bit of initial slop when starting to pedal, then the engagement kicked in solidly. Perhaps there was a break-in period, though, because engagement seemed to improve over the course of several rides. There was a much firmer, active engagement when starting to pedal by the third ride on the wheels. Instant? No, but very good — better than the Firecrests.

The real benefit of this system, though, is the promise of low-drag coasting. Zipp claims you’ll be able to stop pedaling earlier as you approach a high-speed curve without losing speed and pedal less when drafting. This is another intangible that was nearly impossible to gauge out on the road, so we can’t say for sure if we saved any watts or were able to stop pedaling earlier. Some serious lab testing would be necessary to determine if this claim is true, and we imagine it would have a lot to do with the type of bearings being used in the hubs, as well as the condition of those bearings. It stands to reason that the best way to truly reduce drag would be to have the engagement rings in the freehub completely disengage from each other — something Shimano is toying with when its Scylence hubs drop.

The Aerodynamic Boundary Layer Control (ABLC), which we all know as those little dimples on the sides of Zipp rims, carries over from even before the Firecrest wheels, but with a twist. ABLC dimpling — similar to the dimples on a golf ball —addresses an aerodynamic concept called Laminar separation, which occurs when air moves over the surface of an object and then at a certain point separates from that object, effectively creating turbulent drag. ABLC helps airflow adhere to the rim’s surface by “energizing” it, or essentially creating mini-turbulence as the air flows over the surface. In theory, air should then flow more completely around the leeward side of the rim at a wider range of yaw angles.

The ABLC Sawtooth dimpling on the NSWs builds on the original ABLC concept by rearranging the dimpling pattern to address what’s known as the Kármán vortex street, in which air swirls as it leaves the rear of the rim shape, causing turbulence that in turn creates drag and possibly even vibrations that can affect your bike’s handling. The new Sawtooth pattern groups dimples in a sinusoidal orientation as they approach the spoke bed to create small sheet vortices — small circuits of swirling air — at a high frequency but low magnitude. In other words, there are more tiny vortices of swirling air, but they are not as powerful and therefore won’t affect handling and drag as significantly.

“The 404 NSW has a massive drop in side force at higher yaw angles,” says Jason Fowler, Zipp’s wheel product manager, “due in large part to the rim shape and the Sawtooth dimple pattern compared to the 404 Firecrest, which is already best in class (34% side force reduction). The end result for the rider is peace of mind in gusty wind conditions and saving watts that would be expended while attempting to hold your line.”

We didn’t wind-tunnel-test the ABLC Sawtooth versus the older version of ABLC, but if it works as promised, that’s a win for you, the racer, considering the rims generally feel the same as the Firecrests in terms of lateral stiffness and responsiveness. We did notice a stability improvement in Colorado’s strong spring crosswinds: The NSW wheels seemed to dance a bit less in crosswinds than their Firecrest counterparts. Same feel plus lower watt expenditure equals a win.

The other eye-catcher is the Showstopper brake track. It’s a textured track molded into the rim, and as promised, the brakes do, in fact, grab and modulate better than most of the carbon rims we’ve tested recently. On sustained descents, we got a few squeals out of them, but braking power seemed consistent even if the rims sang to us. Get them wet and you’re reminded you’re riding a carbon rim, though: that nothing-nothing-grab feeling still applies here, though certainly to a lesser extent than the Firecrests.

So yes, these are very good wheels, but they pose an impossible question: Should you buy them? The advantages are marginal: coasting with lower rolling resistance, wind-shearing details, freehub engagement. Both the NSWs and Firecrests are rugged, reliable wheels up for any type of racing, but the NSW has those small touches that might mean the difference between crossing the line a tire ahead of another sprinter or standing on the second step, especially if it’s a windy race day. If you’re a top-level racer, those marginal gains are likely worth the cost. The rest of us may be better served to pocket that extra grand and stick with the proven 404 Firecrests.

Spoke count: 18 (f); 24 (r)
Rim Type: clincher
Rim width: 17.25mm internal; 27.8mm external
Rim depth: 58mm
Rotational inertia: 5.09 (f); 5.18 (r)
Deflection: 4.32mm (f); 8.47mm (r)