Zipp 404 Carbon Clincher Wheelset
The Zipp 404 Carbon Clincher is the kind of wheelset we salivate over. It puts together several wheel concepts we like at once. Light weight. Aerodynamic. Wide rims. Sapim spokes. Hubs with adjustable bearing pre-load. A rear hub with an easily-swappable cassette body.
In terms of weight, we're certainly of the mind that if you're planning on riding fast in most conditions, it's better to have a wheel that is a bit heavier and a bit more aero than it is to have a wheel that's a bit lighter but a bit less aero. At the same time, even we are sometimes deterred, or at least find ourselves pausing when looking at heavy aero wheels.
Figuring out where your tipping point is can be tricky. In terms of our own balance, we have a set of Zipp 303 clinchers for the days when we're riding to races. They're not as aero as the 404 clinchers, but we wanted more flexibility in terms of using the wheels on rolling to hilly courses and like the aerodynamics compared to the other clinchers of a similar depth.
Taking a look at the new 404 Carbon Clincher, with what Zipp is calling their Firecrest profile, we see a wheel that's both more aero and lighter than our 303s. Here is the weight break down thanks to our digital scales. The front wheel, without rim strip, skewer, or magnet, weighs in at 710g, the rear 830g (claimed weight is 718g front and 839g rear). It's a savings of 40g per wheel compared to our 303s, and about 60g per wheel compared with the hybrid carbon-aluminum 404 clinchers. The rim strips weighed 19g and 17g—you'll want to use these as they're from Zipp and designed for this wheel. The wheels also came with the new missile-shaped Zipp skewers, which weigh 35g for the front and 39g for the rear.
But as we wrote, weight is only a part of the story. The aerodynamics has to be better for the wheel to be a worthwhile consideration. They appear to be a good bit better, at least in the lab. Zipp says that in the wind tunnel, these new wheels are 80 seconds faster than Mavic Ksyrium's over 40km (the Ksyrium wheels are convenient to test against as they're one of the most popular, if not the most popular, reliable low spoke-count wheels on the market). The 2010 iteration 404 tubular, which doesn't share the new Firecrest profile of the new 404c, is 71 seconds faster; the new Firecrest shape in a clincher gains you nine seconds over the established, pretty-fast 404 tubular.
A good look at the new 404 and you know it is different than other Zipp's, both in clincher and tubular. The only rim that it even vaguely seems similar to is the Hed Stinger 6, a tubular wheel. The rim looks wide and almost heavy. It is wide. The inside width at the tire bead is 16.35mm, the outside width at the same spot is 23.5mm and the rim only gets wider as you go towards the spoke bed. 25.20mm at the bottom of the brake track, and then getting to 27mm wide 36mm from the top of the rim and then turning rather abruptly and flattening in the next 22mm. Looking at the rim with an inflated 23mm wide tire mounted and the overall shape seems almost oval, but wider at the spoke side of the rim.
We've been admiring the wide rim concept for some time. The idea of making rims wider, as wide as the tires used, and mating the rims with 23-25mm tires to improve road grip, smooth out transitions from riding straight to taking a turn, and improve aerodynamics all makes sense to us. The wide rim changes the profile of the 23mm tire from a bulb to more of a U shape. Zipp has been embracing the wide rim concept as well with their tubulars for a number of years, and has already done their 101 clincher as a wide rim, but this is the first time we've seen them bring the concept to their deep dish clincher wheels.
As much as an idea makes sense, it would be good to have some evidence to back it up. Hed, which probably started the wide rim trend, has been taking their time putting out a promised white paper on the subject. Bike Tech Review has a wide rim rolling resistance test posted by a member. The member does a good job of limiting variables and being precise in protocols. The result doesn't find any reduction of rolling resistance benefit to the wider rim; no penalty either. But the test seems limited because it is performed on rollers rather than on a road. We'll continue to search for tests that try to examine whether or not wider rims can reduce rolling resistance, but we do take a little confidence from the fact that the idea was pioneered by small companies and we can see other companies adopting the concept as well. Not only has Hed-advised Trek come out with wider-rimmed deep-section wheels, but so has rim-maker Velocity. Reynolds new 90mm deep tubular supposedly is getting wider, as is Mavic's new 80mm deep tubular . Wouldn't be surprised if this becomes a bandwagon.
The explanation from Hed as to why wider rims should make tires roll better is fairly complicated, but can be simplified to the following: the tire rolls faster because with straighter walls, the tire is deforming less, by squishing less on the sides, as you roll down the road. The people at Zipp add that with increased air volume from the greater width, there is less tire squirm when side-loaded, and you can drop a few psi from the total to get better grip without increasing the likelihood of pinch-flatting. Yes, you may either sacrifice a little rolling resistance or get the tire up to what it would be if you ran a narrow rim, but in the scheme of things, staying upright has its advantages and lower tire pressure can sometimes reduce rolling resistance.
The Firecrest rim shape is not only supposed to be more aerodynamic and optimized for 23mm clincher tires, but the shape is supposed to be more stable as well. By stable this means that the pressure differential between the windward and leeward side of the wheels in a crosswind is not dramatically different. You don't feel like you're holding a sail too tightly in a small boat as you're riding.
How the front wheel reacts to a side wind is what makes steering an issue. With the new design, the center of pressure from a side wind is located slightly behind the front hub, where most wheels have the pressure in front of the hub. By having the pressure behind, the side wind is not pushing you strongly away from the wind, but slightly into it. Only slightly, as the point is close enough to the hub that the effective "lever" length is short, and with the fork rake and wheel direction, it's easy to almost cancel out the force.
The Firecrest shape is such that the rim aerodynamics now work very well not only for the front half of the wheel, as in the leading edge of the wheel, the tire to rim to spoke section as well as the back half, the spoke to rim to tire. When viewed from the back half of the wheel, the shape is almost like a wing; others have suggested it kind of resembles a Toyota Prius or the currently vogue Kamm-tail design. This back half works both on the front wheel, as helping with the above, and on the back wheel, as the back half of the wheel is seen much more by the wind than the front half tucked behind the seat tube.
Despite all this goodness, carbon clincher rims, with their unsupported rim walls, make us a bit nervous. Yes, we know carbon-fiber can be as strong or stronger than aluminum. But carbon fiber can be brittle. And the rim walls heating up significantly while braking never makes us happy. Zipp claims the lay-up makes the rim strong enough. We wonder if making the rim wider reduces pressure a bit as the tire might have less of an inclination to push out. As for the heating up, they claim to have put a new heat-resistant layer at the braking track to eliminate notable heat build up at the tire. Zipp engineers felt this was the big failure of carbon clinchers in the past and they didn't want to repeat it.
Zipp recommends their Tangente Cork Brake Pads for the rims and they ship the wheels with a set of these pads. The reliable SwissStop Carbon King yellow pads aren't recommended as highly but are not prohibited.
We decided to start with the cork pads. Setting up Michelin Pro3 Race tires was easy. Scary easy. We decided to first mount them without tubes to see what kind of effort would be needed to get the tires on, and if they needed stretching, it would happen without the tubes in. They went on without any need of a plastic tire lever. They came off by hand as well. When we added the tube, we still only needed our hands to mount and remove the tires. This ease is due to the re-design, but it's a good thing for carbon clinchers regardless; the thought of putting a lever against carbon-fiber walls is a bit scary. If you need to use tire levers, stick to plastic levers only.
We could barely contain ourselves when we first took these on the road. Our first ride was a 12-mile warm-up en route to a race. They felt fast as we beat out a nice tempo en route. In the race, maybe it was our excitement, but it felt like the wheels were singing when we attacked, though the almost 28mph average speed of the rolling circuit and the 90 some-odd hungry racers made even good attacks seem weak. The wider rim or the all-carbon design, or both seemed to contribute to a laterally stiffer ride. All good. Then we felt our bike jump. The rear skewer had come loose. Ugh! We didn't like the feel of the throw and even though we thought we had tightened it sufficiently, it seems like we didn't. Race over.
The next day, we jumped into an unfamiliar group ride. Here again, the skewer came loose. But on the good side, even in a fast group of guys knowing the route and setting up for the sprint lines we didn't know, we were able to do everything but win the sprints.
Another good sign was going out with some tall, meaty time trial/triathlete hammerheads prepping for the state championships on their tt bikes and deep-dish wheels. We had no problem matching or exceeding their pulls on our standard road bike equipped with the 404c.
The cork pads performed well. They definitely were not grabby and when we poured water on the front wheel while riding and braked (no rain during the test period), the sensation was similar to riding on aluminum rims. After a few rides, we swapped out the cork pads for our SwissStop Carbon Kings. Initially, they felt a bit grabby. Over time, that sensation disappeared. We also did the water test to the wheels with the SwissStops. No change in wet brake performance.
In terms of the wheel's stability in crosswinds, for most riding conditions, we didn't feel like the wheels handled any differently than our daily 28-spoke training wheels. These wheels have a traditional box-section rim design and weigh about the same as the 404c. We did find a few places where there was a little extra buffeting. First was on a curvaceous 46mph descent on a windy day. Felt like we needed a bit more attention to keeping the wheel going precisely where we wanted it. The second was having a tractor-trailer accelerate away from us in the high 30s mph. Must have had an empty trailer. As we were exiting through the turbulent air zone at the end of the trailer's draft, we were pushed around a bit, but that probably could have happened with any wheelset.
As mentioned earlier, one of our abiding concerns with carbon clinchers is that they are too stiff or brittle to stand up to getting pounded by potholes, badly-timed jumps and the occasional hard landing. We had no fear or worry doing slow and controlled curb-hopping, but that kind of force is not the kind that concerns us. At the end of one ride, we slammed into a pothole and pinch-flatted. The wheel was fine. Two days later, we did a poor jump to clear a set of train tracks at the end of a downhill. Cleared no problem, but the landing was less than ideal, onto some cracked pavement. There, too, even though there was a noise, the rim was fine.
While we don't think we noticed a difference in rolling resistance or comfort due to the wider rims, and we didn't try to find the limits of their cornering ability, we loved how the wheels moved when hammering the flats. Moving from lower speeds to higher speeds seemed to have a bit less of a momentum shift than we're used to with deep section wheels. On the moderate hills, we noticed no penalty. Even on the steep stuff, while the wheels didn't feel sprightly, they also didn't feel like they were weighing us down. The Zipp 404 Carbon Clincher is exciting; we can't wait to see what else Zipp does with the Firecrest shape.