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.