Author's Note: This is not a full review. Please do not treat it as such. Instead the objective is to illuminate Mavic's claims about its new carbon clincher wheels, and present our very preliminary impressions (aka: one test ride). RoadBikeReview will have these wheels for an additional week before returning them to Mavic, and will present follow-up impressions soon after.
The carbon clincher is a curious beast. Over the years it seems to have created equal parts ecstasy and agony. They look great and allow users to reap at least some of the benefits of carbon aero wheels without the headaches of gluing and maintaining tubulars.
But they also have drawbacks. Unlike aluminum, carbon fiber does a poor job of dissipating heat, and that can be a real problem when you're bombing a long descent. You grab the brakes, heat builds up, and the next thing you know you're on the side of the road repairing a flat - or worse.
In February 2012, organizers of the popular Levi's Gran Fondo went so far as to ask participants in the popular, mass-start amateur road ride in Northern California to not use carbon clinchers at the event. "Please leave them at home," read the communiqué. "Carbon clincher wheels are strongly discouraged because they can fail/explode under the extreme braking necessary on sections of this route."
Of course anyone who's ridden Levi's ride knows that there are some extremely steep descents, making this request at least in part a case of Cover-Your-Ass diplomacy. But there's no denying that the carbon clincher experience can be interesting if nothing else. Warped rims, sometimes dubious braking effectiveness (especially in the wet), tire blowouts, and the ever-present shrill can leave you questioning whether the convenience and aero efficiency is worth the trouble.
But that's a debate we are going to steer clear of. Love them or loathe them, carbon clinchers are here to stay. And the new Mavic Cosmic Carbone 40C's are a player in that market.
The Mavic Party Line
During our one-on-one sit-down with Mavic PR man Zack Vestal on March 20, he walked us through the chronology that brought us to this point. That story started with an explanation on why the famed French wheel maker was so late to the party, as this is Mavic's first carbon clincher wheelset. (Actually they are a carbon-alloy hybrid, but more on that later).
"The reasons boiled down to the engineering challenges of maintaining structural integrity, withstanding braking heat, and coming up with a solution that is actually beneficial in terms of weight and rim shape," he said. "We've seen many examples of carbon rims being flared out due to heating of the clincher bead, and the reality is that after some time, the industry has recognized that they are not the best wheel choice in all situations."
Of course some of this is truth, some is PR speak, and some of it is Mavic being Mavic. Early adapter is not necessarily part of the company's mission statement. But they do have a long history in the wheel-making realm, so some benefit of the doubt is warranted.
Whatever the case, after three years of development, the Mavic Cosmic Carbone 40C was born. Retail price is $2,750 and they'll become available to the North American public starting June 1. They are 40mm deep, 19mm wide, and weigh 1545 grams per pair, which as any wheel aficionado knows, is a decidedly middle-of-the-road number in this game.
"We never win the weight war because we build durability," explained Vestal. "Weight was not the driving motivator. Building a safe, durable, nice riding carbon clincher was the goal."
For comparisons sake, which Mavic did a lot of during the presentation, Zipp's 303 Firecrest 45mm carbon clincher weigh a claimed 1475 grams and the Reynolds 46mm clincher comes in at a claimed 1440 grams. However, as Mavic was quick to point out, these numbers do not include rim tape, which their new wheels do not need (more on that soon).
"That can be 25-30 grams per wheel or more," said Vestal. "So the differences are not as big as they might seem."
For $2,750 you get wheels, wheel bags, QRs, brake pads, and tools
Mavic also claims that due to their new offering's unique design, the Comic Carbone 40C actually have the lowest inertia weight of the three. Obviously we haven't verified this, but that is what they said so we'll pass it on. It's also worth noting that their presentation only looked at these three wheelsets. There was no mention of ENVE or Mad Fiber who also have wheel offerings in this category.
The real meat of this story isn't about weight, it's about the way Mavic claims to have addressed those aforementioned carbon clincher issues, primarily heat dissipation and bunk braking.
"That is where our unique engineering approach came in," explained Vestal, who went on to offer this laundry list of features.
-- The wheels use threaded inserts in the spoke bed. This is done to help distribute spoke load, ensure tolerance, and means no cutting of the actual rim bed which would otherwise create weakness. This is done using what Mavic calls its FORE process, where a big oversized thread receives the spoke nipple (see diagram).
-- Because of this, there is no need to add carbon fiber along the spoke bed, so you have consistent wall thickness. That consistent surface improves braking and allows for easy service because the nipples are accessible from the outside.
-- The tire bed itself is a thin aluminum insert with carbon fiber wrapped around this alloy core (thus making it a hybrid). By using aluminum for the bed and bead hooks 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. The bed's un-impaled state also means no rim tape is needed, reducing overall weight. However, they are not tubeless compatible.
Carbon and aluminum working together.
-- Utilizing what it calls a secret sauce blend of two resins that wont melt, Mavic claims heating is not an issue. That means no warping, bulging, or any other catastrophic occurrence.
-- More secret sauce is in play when it comes to the surface treatment on the outside of the wheel, which gives it a slightly raw, abrasive feel as is designed to improve braking. This point was hammered home later, when RoadBikeReview was shown a slide that claimed in dry conditions our three-wheel sample size all stopped at about the same rate. But mix in an afternoon thunderstorm and the Cosmic Carbone 40C came to a halt in less than half the distance, 43 meters versus 88 and 91, claimed Mavic. We don't know what the exact protocol was, but it's a pretty significant safety claim and one that Mavic is hanging its hat on.
-- Mavic also addressed the issue of what happens when two disparate materials such as aluminum and carbon fiber are bonded together and then subjected to immense heat. All else being equal, different materials typically expand at different rates, which would lead to a breaking of the bond. But Mavic says another super secret sauce that is a chemical bond not a mechanical bond keeps things together. "The way it's been explained to me is that it's a living junction that gets stronger over time," said Vestal. "So basically our engineers are saying it's not a problem. These wheels are meant to perform in all conditions."
-- As for the all-important aerodynamic considerations, which is why many people will be interested in these wheels in the first place, Mavic basically said the Cosmic Carbone 40C was decent, not great. Utilizing a chart that compared the new CC40C to the Zipp 303, the two tracked a similar line until the 12-13-degree of Yaw range, where Zipp won out. Further down the spectrum the two competitors came back together.
-- Finally there is the question of why, as in why do people really need wheels like this given there inherent drawbacks and production difficulties, not to mention the stiff $2750 price tag. "Some people will argue that if you really want the lightest, most aero carbon wheel then you should be running tubulars," said Vestal. "But that is not realistic for most people who are not proficient in gluing tubulars and don't want to risk the hassle of flatting a tubular. So instead you can ride aero shapes in a clincher format with lower weight, safety, reliability and get the undeniable aesthetic."
- 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
Very Preliminary First Impressions
My one and only ride on these wheels thus far was a 20-mile jaunt up Boulder's Super Flagstaff climb with nearly 3,000 feet of ascending -- and the accompanying descending. (You can check out the Strava File here.) It was not raining, so I have no opinion on wet-weather braking efficiency yet.
What I can say is that the dry-weather braking was consistent and predictable, with no grabbing, pulsing or fading. And with pitches in excess of 17 percent coming down, it felt like a legitimate, if not brief, test sample. So thumbs up there. Stiffness was also not an issue, something which Mavic claims is 10-perecnt better than the competition.
What Mavic did not solve is the shrill noise that most carbon clinchers produce when you grab a lot of brake. Instead the din ranged for a whirring hum during gradual braking to a loud whistle when digging deep. But this shouldn't necessarily count against the Cosmic Carbone 40C's since this cacophony issue plagues most if not all carbon clincher wheels. It just needs to be pointed out.
After the ride, I called Mavic's Vestal and he seemed to think some of this noise could be eliminated by toeing in the brakes, and also suggested that there may be a subtle bedding-in phase where noise will gradually decline. We'll keep climbing and descending next week and let you know if anything does change.
One ascetic issue we noticed was that some of the coloring from the yellow SwissStop brake pads was wearing off onto the wheel's braking area. Vestal said he'd also seen this during 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. Again, we'll get back to you on this.
Bottom line, the RoadBikeReview first impression is that the new Cosmic Carbone 40C delivers on its promised high-level braking performance, while at the same timer maintaining stiffness and acceptable -- but not exceptional -- weight. And for whatever it's worth they look pretty cool, too. But nobody buys carbon clinchers for the looks, do they?