Mavic finally has a full-carbon clincher. Two, actually: The 40-millimeter-deep Cosmic Pro Carbon SL C and more endurance-oriented Ksyrium Pro Carbon SL C. After three days of riding both in the mountains around Nice, France, we’re confident saying they’re not only fast and precise, but that they offer the best braking of any rim-brake carbon wheels we’ve encountered.
Questions of durability will, of course, require further testing. But initial impressions are that the venerable French brand has upped its game.
Until now, Mavic has used aluminum inserts in its carbon clinchers, saying that was the only way to create a clincher that lived up to the company’s internal safety and durability standards. As full-carbon wheels proliferated, however, the brand ended up seeming a bit behind the times. But after years of development, Mavic has come up with a new full-carbon construction method that it claims offers best-in-class durability and braking, with a much higher melting point than other carbon rims. (Heat from braking can melt resin, which can warp brake tracks and lead to complete rim failures.)
Both wheelsets feature 17-millimeter internal widths and will be available in disc and rim versions. The rim versions will retail for $2,200 when they hit stores (March 15 for the Cosmic and June 1 for the Ksyrium). Claimed weights for the Cosmics and Ksyriums are 1,450 and 1,390 grams, respectively. The disc versions will retail for $2,400 and will go on sale April 15 (Cosmic) and June 1 (Ksyrium).
The stopping prowess is down to a new laser treatment that melts away resin in the first layer of carbon fiber along the brake track. Cured-resin surfaces are too smooth for effective braking. Wheel manufacturers employ various methods to combat this, including adding other materials or etching patterns into the brake track. Mavic previously used a form of sand blasting to add texture.
Extra materials obviously add weight and manufacturing complexity, while methods like etching and sand blasting can compromise the integrity of the carbon fibers in the outer layer. Mavic’s treatment — which involves a single pass of a precisely calibrated laser — melts away just enough resin to expose the outer layer of carbon fiber without compromising the individual fibers. The brake track is, essentially, bare woven fabric.
The result: Stopping performance in wet conditions is almost exactly the same as in dry, with confidence-inspiring consistency and modulation. Once we got the hang of things — the rims’ bite is startling at first — we were able to take disc-like lines into downhill switchbacks.
The pads hitting the fabric of the tracks produces a sound sort of like the whine of a Formula-1 car. It’s not annoying — in fact we grew to like it — but it’s definitely noticeable. And judging by the amount of rubber tailing off the ends of our pads by just the end of the second ride, it’s a safe bet that these wheels will require frequent pad replacements. But that seems a small compromise for braking this good.
Development of the wheels was led by Mavic’s head of composites R&D, Jean-Christophe Minni, who came to the company two years ago after a career in the aerospace industry. One of his major advances was a construction method that allows Mavic to deliver seamless carbon clincher contours straight from the mold, without the need for machine finishing, which, Minni says, can compromise the integrity of the outer layers of carbon.
More importantly, he developed a curing process that produces resins capable of handling temperatures up to 200 degrees Celsius. Mavic claims that the resins used in most carbon rim manufacturing melt at temperatures well below that point, which leads to failures. The company says that at last year’s l’Etape du Tour, where it provided rider support, Mavic reps encountered 52 riders with wheel failures. Of those, 38 were carbon clinchers (though the company couldn’t say how many were down to melted rims, versus cracks or other issues).
Mavic employed aluminum inserts in its previous generation of carbon clinchers to dissipate heat and keep temperatures below the melting point. While there are curing processes that can deliver a melting temperature (Tg) above 200 degrees Celsius, Mavic claims that they are too time-consuming and expensive for wheel manufacturing. Even with iTgMax (Mavic’s name for its new rim technology), the company can produce only 300 wheelsets per week at its factory in Romania. And the company’s engineers claim that even under heavy, sustained braking on long descents (the main testing ground is Mont Ventoux), its rims don’t see temperatures in excess of 200 degrees.
In our initial test rides, the Cosmic Pro Carbon SL C wheels, with 25-millimeter tires and the now-standard blunt aero profile, spun up quickly and remained stable even in strong coastal crosswinds.
The Ksyriums, with a 26-millimeter profile, have a claimed weight only 60 grams lighter than the deep-section Cosmics. That’s not much of a difference, but all of the weight comes out at the rims. The result is that the Ksyriums do seem to spin up faster, especially on climbs. Between that and the superb braking performance, we’re looking forward to throwing these on our climbing bike for some longer-term testing. Our hunch is they’ll become a favorite.
Both sets are 18-hole front and 24-hole rear and come laced to aluminum hubs built around sealed cartridge bearings and Mavic’s Instant Drive 360 freehub. The Cosmics come with bladed, double-butted steel spokes, while the Ksyriums have slightly lighter standard steel spokes.
The disc versions of both will feature the exact same rims, minus the laser treatment. Despite the common perception that disc wheels can be built up with lighter rims, Mavic says most of the weight in its new rims is due to materials and construction needed to deal with impacts, tire pressure, and lateral stiffness, rather than braking forces. Potential weight savings in a disc-only version, according to the company, would be minimal.
Mavic will launch the wheels alongside a new worldwide demo program involving select retailers who will have specially branded (tricky to hide if you steal them) Cosmics and Ksyriums. Consumers will be able to book test rides online then throw the wheels on their own bikes for testing. That program rolls out May 1.