Mavic

Cosmic Pro Carbon SL UST Wheelset - Tubeless

While tubeless setups have taken off in far the distant land of mountain bikes, they've had a much slower reveal on the road side of things. Maybe it's due to roadies' affinity for tradition. Maybe it's a bit of stubbornness. Or maybe we just needed the reassurance of the industry's first tubeless crafters to step into the market and fulfill the big promises that a tubeless setup grants without the massive pain of setup that we've seen from other tubeless designs. And so we're eager, excited, and (admittedly) maybe a little too giddy to get our hands on the Mavic Cosmic Pro Carbon SL UST Tubeless Wheelset.

This lightweight wheelset takes road tubeless to the next level. As with most tubeless setups, it reduces weight, puncture potential, and PSI for less rolling resistance and more comfort. The deviation comes in ease of installation: the tires pop-on without tire levers and inflate without a compressor, CO2, or high-volume floor pump. Just use the same beat-up old pump you've been repairing the hose on for years—though we do recommend sticking with Mavic's UST-specific tires, which come stock on the rims.

Some of us were under the impression that Mavic was sitting on the backburner while the road tubeless scene started to boom, but with the unveiling of Road UST it is evident that we couldn't have been more wrong. Instead, it's apparent that there was a certain level of patience and discipline exhibited while Mavic's engineers were hard at work perfecting the technology, prioritizing safety and ease of use before release. The result is a tire and rim interface that were designed in conjunction with one another, harnessing all of the benefits of tubeless that we crave, like lower rolling resistance and puncture resistance, and skipping the downside that has most cyclists complaining—tire installation. Since road tires require much higher pressures and sit on narrower rims, the tolerances were tighter than on MTB wheels, so Mavic took its time until total satisfaction was achieved, with less than a millimeter of tolerance on the tire that assures you the tire will go on with ease, and stay on.

Of course, some of us found frustration from this level of perfectionism, though that kind of stubbornness and patience is only negative if you value industry trends over proven, effective, and safe technology. To illustrate the point, consider that at a recent sportive event associated with that big race in France, Mavic reportedly provided neutral service support for 38 instances of carbon clincher failures. This tells us what Mavic knew all along: delamination, deformation, cracking, and the like are all still common occurrences in the carbon wheel world. To deal with this, Mavic has long used aluminum inserts in its carbon wheels to serve as reinforcing spines and heat sinks. The risks of full-carbon rims were unacceptable to the brand, which is built on reliability, safety, and longevity as much as it is low weight and aerodynamics — all of which are reasons why generations of cyclists have been grateful for that stubbornness.

The brand recently poached an engineer from the aerospace indsutry, one Jean-Christophe Minni, and gave him two years to develop carbon fiber technology that would allow it to assuage its own concerns with the safety of composite materials. The full-carbon Cosmic Pro Carbon SL UST is the result. Minni's construction process produces rims that can withstand a claimed 392 degrees Fahrenheit before the resin begins to detach, and braking tests on descents like Mont Ventoux and the Col de la Madone — which blend tight switchbacks and long, sweeping sections — don't cause the rims to approach that temperature threshold. This towering tolerance may seem like overkill while you're sitting on the couch browsing Competitive, but we can confirm that it's very reassuring during 20 minute descents that require a bit of brake drag. And that's why Mavic is such a trusted name in the cycling industry. The brand leaves nothing to chance.

While that heat resistance is mostly about improvements to resin, deformed rims aren't the only wheel failure woe Mavic's iTgMax technology addresses. The all-important layers of material in the tire bed are wholly intact. There's no cutting fibers, no Frankensteining, no creative gap filling, and no machine finishing. By keeping each layer intact and not disturbing the finished product, Mavic reduces the chance of introducing the artificial weak points that plague piecemeal carbon lay-ups, maintaining a solid surface for increased structural integrity. Instead of a puzzle of carbon fiber scraps glued together with resin, the carbon is already a unified piece.

The brake tracks themselves are finished with lasers. Our shared cultural imagination typically treats lasers as precision finishing instruments, tools applied with a surgeon's delicate discretion in order to meet impossibly meticulous manufacturing standards. The opposite is true for brake tracks, though, as Mavic uses the lasers in order to literally rough the rims up. The lasers are the sci-fi equivalent of sand paper, removing the outer, smooth layer of resin to expose a more erratic texture that better grips the soft, SwissStop Yellow King brake pads shipped with the wheels. And we should stress that the Mavic-yellow pads are soft. Given that softness, a fair amount of sloughed-off material (in the form of yellow powder) and more frequent pad replacement are the only immediately obvious downsides to the wheelset's exceptional braking. Mavic claims harder, more durable pads will work, but we strongly discourage it as they may damage the rims. We like the idea of the pad shredding much better than the rim shredding. Plus, the harder pads won't be Mavic yellow. Aesthetics matter—especially with a brand and color so significant in cycling.

When the pads engage the exposed fabric of the rims' brake tracks, the wheels emit a sound like the whir of a jet engine heard at a distance that's not unlike the sound of Mavic's Exalith brake tracks. It's a reassuringly positive indication that the brakes are engaged, and the sound is especially welcome as a warning to those around you while riding in a group or pace line. It's essentially the French brand's aural version of brake lights for bicycles, and given how responsive the braking is, that signature whirring is almost a necessity. With each new generation of carbon wheels, we're bombarded with claims of carbon braking that's so good it rivals or is better than alloy brake tracks—you know the drill. This time, those claims are actually true, and we suspect it's another part of the reason why Mavic took its sweet time sending the full-carbon rims to market.

In addition to improved braking, the rims also feature a new aerodynamic profile that Mavic claims compares favorably to some of our top-selling wheels in the 40-50mm range. The French brand credits the Cosmic Pro Carbon SL with saving 2.3 watts across yaw angles up to 10 degrees, which means the aerodynamic properties don't disappear as soon as you take the wheels out of the wind tunnel and onto the actual roads. The new profile is less pointy than Mavic's usual models. Instead, it features a dramatically blunted inner face and represents the most radical departure from a pure NACA airfoil shape from the stubborn French firm to date. The shape better manages oblique resistance, combining the aerodynamic benefits of deep rims with additional crosswind stability.

With all the excitement about the new rims, it's easy to overlook the Cosmic Carbon SL's Instant Drive 360 hubs. The hubs represent yet another drastic departure from tradition, as the engagement mechanism replaces the usual pawl system with the dual-ratcheting rings formally found only in designer hubs on custom hand-builts. The design involves two rings that press together laterally. One face of the rings' teeth are sloped, so they ramp off of each other while freewheeling. The other face isn't, so the rings engage with pedal input. The design cuts the engagement angle down to nine degrees, a number we might expect to see on a mountain bike hub but are pleasantly surprised to find on the road.

As metioned above, the wheels ship with Mavic-branded SwissStop Yellow King brake pads. We recommend only using this model of pad. The axles are hollow, which allows for conversion to different axle standards by using various end caps. The wheels also ship with Mavic's 25mm Yksion Pro UST tires for the front and rear, ensuring you hit the road with the exceptional attention to detail that went into crafting the wheelset.