Our test rig is a Parlee Z5sl with SRAM Red, except for Rival cranks to accommodate a Stages Power Meter and Rotor Q-Ring chainrings (52x36).

First, let's get some important details out of the way. Due to limited availability of test wheels, RoadBikeReview was only able to log four rides on Mavic's new Cosmic Carbone 40C carbon clinchers before having to return them. Thus we can only label this a short-term review.

That also means we did not get a chance to ride them in wet road conditions, which for some potential buyers will be a very important consideration. The reason being is that among several heady claims, Mavic says its new $2750 carbon hoops are far better than Zipp's 303 Firecrest or the Reynolds 46 when it comes to wet-weather braking. In fact, during internal testing, Mavic claims the 40C's stopped in less than half the distance, 43 meters versus 88 meters and 91 meters respectively.

Like we wrote in our initial assessment of the wheels, which you can read here, we don't know exact protocol for those braking tests, but it's a significant claim and one that Mavic is very proud of. (Obviously, if we get another crack at riding these wheels, we'll do our best to (safely) test stopping distance in wet weather.)

Like all Mavic wheels, the Cosmic Carbone 40C are part of a wheel-tire system. These come with a 190-gram, dual compound 120 TPI GripLink front tire and PowerLink rear tire.

What We Did Learn

From the beginning, Mavic has been pushing these new wheels as a best-in-class performer when it comes to safety. During its product launch, the France-based wheel-and-apparel maker made a PR push to point out past instances of carbon clincher failure, and proudly beat its own drum when it came to its new wheels' braking performance and overall safety.

Some might argue this was a subtle attempt at scare tactics. We'll simply say that during our four test rides, the wheels performed as advertised. Dry-weather braking, even at speeds in excess of 40mph, was consistent and predictable, with no grabbing, pulsing or fading. And there were no catastrophic failures to speak of.

Each of our rides took place in the hills around Boulder, Colorado, and included significant climbing and the requisite descending, with downhill pitches of at least 8 percent, and one near-quarter-mile-long section that's over 17 percent. Here are the four Strava files from our test rides:

Based on our admittedly small test sample, it appears Mavic has overcome some of the past material problems, which centered on inconsistent braking and carbon fiber's inability to dissipate heat. As a refresher, when heat builds up in a carbon fiber wheel, bad things tend to happen: warped rims, dubious braking effectiveness, and tire blowouts to name a few.

To alleviate the braking issue, Mavic used what it calls a proprietary surface treatment on the brake track, and this treatment is in the resin itself, meaning it will last the life of the rim.

Mavic also utilized threaded inserts in the spoke bed. That means no hole drilling in the tire bed and no added carbon fiber along the spoke bed, which results in consistent wall thickness. In turn, this consistent surface improves braking and allows for easy service because the spoke nipples are accessible from the outside.

The alloy rim bed is not drilled meaning no rim tape needed. However, they are not tubeless compatible.

The tire bed itself is a thin aluminum insert with carbon fiber wrapped around this alloy core. By using aluminum for the bed and bead hooks, the idea is that you get improved tolerance, and no risk of damage from tire levers. Alloy also adds impact resistance, because unlike the directional nature of carbon fiber's strength, aluminum can handle loads in multiple directions.

Now comes the ubiquitous secret sauce. Utilizing what it calls a blend of two non-melting resins, Mavic says it's solved the issue of warping, bulging, or any other catastrophic occurrence. At this point, we cant prove any of this, but obviously we didn't encounter any catastrophic occurrences either.

Mavic also addressed the issue of what happens when two disparate materials (in this case aluminum and carbon fiber) are bonded together and then heated. Normally this results in differing rates of material expansion, which leads to a broken bond. But Mavic says another spoonful of secret sauce keeps things together. "The way it's been explained to me is that it's a living (chemical not mechanical) junction that gets stronger over time," said Mavic PR man Zack Vestal. "So basically our engineers are saying it's not a problem. These wheels are meant to perform in all conditions."

Again, we cant prove or disprove these claims except to say the wheels performed as advertised during our test time.

The Cosmic Carbone 40C also get a thumbs up for stiffness, which is another Mavic selling point. They claims the new wheels are 10-percent stiffer than the competition. And while I have no idea where that number comes from, or if it's valid, I can say that during aggressive out-of-the-saddle efforts going uphill, downhill, and on the flats there was no brake rub.

However, Mavic did not solve the occasional loud shrill that is part-and-parcel with most carbon wheels. Under moderate braking force the 40C made a low-level whirring noise. Dig a little deeper and they let out a full-fledged squeal. And that noise pattern was just as prevalent on our first ride as it was on our last.

Afterwards, I asked Mavic's Vestal if he thought the brake noise would eventually diminish. "Occasional brake noise is generally part of the carbon clincher package," he said. "However, it should diminish over time or may be resolved with a little effort at brake pad toe in adjustment."

Another issue that was more aesthetic in nature was that some of the coloring from the yellow SwissStop brake pads was wearing off onto the wheel's braking area during our first ride. Vestal said he'd also seen this during his personal test rides, and acknowledged that it might be a case of accelerated pad wear due to the special treatment on the wheels, or it could be part of the bedding-in phase.

With a little hindsight, the guess here is that it was part of the bedding-in phase, as this yellowing had stopped by our fourth ride. What we don't know is how quickly the pads will wear out over the long term. The guess is that users may experience somewhat accelerated pad wear, because as Mavic says themselves, the wheels have an almost raw texture in the braking area (think very light sandpaper grit) which would naturally wear away another surface quicker than if the brake track was smooth alloy.

Now The Bad News
Carbon and aluminum working together.

During its initial presentation of the new Cosmic Carbone 40C, Vestal admitted that Mavic never wins the weight war because they "focus on durability." And indeed, at 1545 grams per pair, these hoops wont wow any of the weight weenies out there.

On the plus side, the 40C requires no rim tape, which is a net gain of 30-40 grams depending on which brand of tape you choose. For example, Velox cloth rim tape is listed on several websites at 16 grams per wheel, while SRAM-branded nylon tape is listed at 18 grams per roll. By comparison, Zipp's 303 Firecrest has a claimed weight of 1475 grams and the Reynolds 46mm clincher comes in at a claimed 1440 grams, but both require rim tape during set-up.

Mavic also claims that due to their new wheels' unique design, the Comic Carbone 40C rims have exceptionally low inertia weight (think lower rolling resistance). Obviously we couldn't verify this during our short test time, but that's part of the message so we'll pass it on.

Where these new wheels don't make up ground is in depth and width. The 40C are 40mm deep versus 45mm and 46mm for the Firecrest and Reynolds. And the 40C's width is listed at 19mm wide, which is also less than the competition. Mavic's rationale here is a common refrain - safety first.

"Aerodynamics are generally enhanced by a wider rim," admitted Vestal. "But in the case of 40C, Mavic's first goal was to make a reliable, safe carbon clincher that brought some genuine performance benefit, including lighter weight, low inertia and low rim weight. The top 40C design goal was to keep the rim as light as possible for low inertia without sacrificing durability. By contrast, many carbon clinchers require overbuilding of the rim to withstand brake heat and radial impacts. So, any aero benefit of a wider rim wasn't top priority."

Mavic says these wheels were in development for three years.

Certainly plenty of consumers wont buy this explanation, since the primary reason they want a carbon clincher is for enhanced aerodynamics without the hassle of gluing tubulars. But Mavic is convinced many other would-be carbon clincher buyers will be won out by the all-purpose reliability and decent aero numbers of the 40C.

"When the Ksyrium wheels were introduced 12 years ago, they were hailed as the all-purpose, do everything wheel solution," said Vestal, alluding to Mavic's longtime flagship alloy wheel. "They also earned a reputation for long-term durability. Well, these new wheels are meant for the same rider who wants one pair of wheels to do everything, every day. On top of that we believe our rim shape is actually quite good in the wind, especially across a wide range of wind angles. It's not the fastest wheel at every yaw angle, but it's quite stable at extreme yaw, which is a benefit."

Obviously, we did not have a change to run these wheels through a battery of wind tunnel tests, but in the light winds we encountered during test riding the wheels were never overly buffeted.

You can't deny that these are seriously slick looking wheels.[/TD]

Bottom Line

The answer to the question, should you buy these wheels has a lot to do with what you are looking for in a set of wheels. Obviously they are not cheap, but anyone shopping for carbon clinchers has likely already gotten past that hurdle. They are also not super light, but again carbon clinchers are not meant to compete with wispy climbing hoops. And finally they are not exceptionally aero compared to some of the competition, but this was not Mavic's primary aim with these wheels.

What the new Mavic Cosmic Carbone 40C does deliver is reliable braking performance and claimed long-term durability. And that's something that should not be understated. When you fully trust that a wheel is going to perform exactly the way you want it to, you'll be more willing to dive hard into corners and open up the throttle on long downhill descents. That equals increased speed, which is what we're all chasing at the end of the day.

  • Reliable and predicable braking
  • Stiffness during hard efforts
  • No tubular tire gluing required
  • Alloy rim bed insert increases strength
  • No rim tape required
  • Attractive aesthetics
  • Ease of spoke servicing
  • Low inertia weight
  • Narrow rim profile
  • Shallower rim depth than core competitors
  • Middle-of-road overall weight
  • Braking noise
  • Price

Overall Rating:
3.5 out of 5

Complete Specs:
  • Price: $2750 including wheel bags, tires, tubes, brake pads, tools, QRs
  • 1545 grams per pair (670g front/875g rear)
  • No added weight from rim tape
  • 2085 grams for complete wheel-tire System
  • 40mm deep profile carbon rim with 19mm outside width
  • Carbon hub shells with aerodynamic aluminum flanges
  • QRM+ adjustable preload bearings and aluminum axles
  • Bladed/butted stainless steel spokes with external, integrated alloy nipples
  • 16 radially laced spokes in front; 20 laced radially non-drive/1-cross drive
  • Wheel-tire system with 190-gram, dual compound 120TPI Mavic GripLink front tire and Mavic PowerLink rear tire

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