Mavic Cosmic Carbone 40 C wheels - first look and ride

Alloy and carbon rim combination for new clinchers

After last year's successful launch of the CXR 80 aero wheel we were expecting Mavic to roll out the lessons learned over their existing line, especially with regards to improved aerodynamics. That's exactly what's happened with the new Cosmic Carbone 40 C. 

The 'C' stands for clincher and, in a first for Mavic, it's all carbon – well, from the exterior at least. As head of wheel design Maxime Brunard explained to BikeRadar, we're actually looking at a complex mix of carbon, speciality resins and an aluminium core.

The Cosmic Carbone 40s aren't the lightest, but at 1,545g for a 40mm-deep pair (2,085g including tyres) they aren't heavyweights – it is a wheel/tyre system after all, with the package including the 190g Yksion Pro tyres.

Mavic do, however, claim that the wheels are the best in terms of other features real-world riders are looking for. Firstly, superior and consistent braking – in the dry they supposedly match the best carbon clinchers on the market, but in the wet they claim a braking distance twice as short as the best of the rivals, and even shorter than Mavic's own alloy rims.

Secondly, stiffness, which is claimed to be 10 percent greater than the best of the competition, and close to 50 percent better laterally for the whole wheel. This could make brake rub a thing of the past.

The pair weighs 1,545g

Finally, the Cosmic Carbone 40 is meant to be an easy wheel to live with – simple to maintain and repair, with strong component parts and tough construction, with consistent braking in any conditions. 

Mavic hope these benefits, plus a price that won't break the bank (€2,000 for wheels, tyres, tubes, skewers and bags; UK and US prices to be announced), should see the wheels become the number one choice for committed sportive riders.

Alloy/carbon fusion

For a long time, Mavic have been at the forefront of wheel technology, but in recent years they've fallen behind the competition on carbon clinchers. They've explained that creating a wheel that's light and strong enough and has the consistency of braking they'd expect is a tough job. 

They admit that some of the competition have achieved this but that prices then become prohibitively expensive. Not that the new Cosmic Carbone 40s are going to be at the budget end of the spectrum.

The challenge in designing the wheel has been in dealing with the stresses on a clincher, which Mavic define as three distinct physical forces:

  1. Air pressure – the force of the tyre pushing on the rim bead
  2. Ground impact – bumps and hits transmitted through the tyre
  3. Brake pressure – forces pushing  on the rim wall's brake surface

Aside from these mechanical forces, the biggest problem has been heat build-up. A long descent with heavy bouts of braking will see rim temperatures exceeding 200°C/400°F, so Mavic's new clincher had to be able to manage and surpass those figures with no adverse effects.

The brake track is carbon - backed by alloy

Both carbon and alloy have pluses and minuses when used as a rim material – aluminium alloy dissipates heat effectively and the brake surface can be machined post-manufacture to be perfectly smooth, but its relatively soft surface is prone to wear and score damage. 

A carbon rim is lighter and lends itself to more complex aero shapes. Plus, if moulded with enough care it can be as smooth as a machined rim. It's strong for its given weight, and won't wear out like a alloy rim. However, while carbon fibres aren't affected by temperature at all, the resin that gives them structure can be seriously affected. In the worst cases, it will hit its glass transition point, referred to as 'Tg'. When this happens the resin will revert back to its liquid form and your rim will fail. 

We've already seen the likes of Zipp, HED and ENVE putting plenty of work into combatting these problems, but all those companies are firmly routed in carbon. Mavic's history in both alloy and carbon has led to them developing a way to combine the two materials; one that's very different to using an alloy rim with a carbon fairing bonded to it.

A super-light alloy extrusion is the basis of the rim. It remains undrilled so there's no need for rim tape, saving a few grams, but isn't tubeless compatible (we think Mavic might be missing a trick here).

The spoke bed is more rounded than past Carbones

The alloy extrusion is bonded within the carbon structure. Mavic go to great lengths to explain that this isn't a mechanical bond (ie, glue) but a chemical one – both the carbon and alloy have a proprietary treatment process that's taken years to perfect. They also claim that the bond will strengthen over time, not weaken as a traditional alu/carbon hybrid could – whether that's true remains to be seen, but it's a very bold claim.

The carbon on the brake track is combined with a new resin Mavic call 'Tg Max'. It is, in fact, made up of two different resins with distinct Tg temperature ratings, the idea being that mixing the two achieves heat resistance without creating the grabby brake feel some carbon surfaces can generate.

Through the layup, this 'secret' resin and the way it's treated, Mavic claim to have improved all-round performance and created a rim that surpasses an alloy-only version in terms of wet weather performance.

The rim is joined to the new carbon/alloy hubs via bladed spokes that thread into alloy inserts bonded to the rim's inner edge. The rim profile now has a more curvy inner edge to allow for this, as opposed to the distinct sharp edge of the previous Cosmic clincher.

Mavic have used their Fore drilling design and large spoke nipples, the claimed advantage being that it's easier to service and replace spokes without the hassle of internal or hidden nipples.

The 40 C uses the same carbon/alloy hubset as Mavic's CXR80

Prototype testing

Aside from the usual testing in Mavic's Annecy labs, which emulates heavy and sustained use, the wheels were subjected to months of trials on Mont Ventoux. The wheels were used for multiple high-speed runs down the 10km descent, with the 100kg test riders (some attached ballasts to reach the target weight) dragging the brakes to induce heat. 

The rims were fitted with heat sensitive patches, which recorded the maximum temperatures reached. After the tests, each wheel was evaluated and analysed, and only Mavic's strict standards were reached was the clincher given the go ahead.

The shape has been optimised in a wind tunnel, too. It's not claimed to be the fastest, but offers good all-round capabilities at all (yaw) angles of wind. The shape is closer to the rounded profiles found on the latest designs from competitor brands, and is worlds away from the blade-like profile of the old Cosmic. Mavic have resisted the urge to go for a wider rim, at a fairly slim 19mm.

We tested the wheels on a mountainous circuit

First ride impressions

We've had the chance to ride the new 40 Cs on a 110km loop out of Pellion, north of Monaco. We took in, amongst other climbs, the Col de Braus and the challenging descent from its peak, which takes in numerous tight, fast bends. 

On the climbs we could feel the relative lack of mass at the rim, making for little in the way of inertia when accelerating into steps in gradient. It's easy to maintain a constant speed, too. 

What we've all been wondering, however, is how they descend. On the plus side, the construction is as tight and stiff as a Ksyrium, with no amount of sprinting and honking on the bars or leaning over in a corner inducing any sort of brake rub.

We found the braking strongly positive

As for the braking, it's consistent, strongly positive and predictable. It feels instant, with less in the way of feel and modulation compared to an alloy rim; it takes some getting used to, and braking later into corners becomes a viable option. 

On the minus side it does suffer from some noise, but box-fresh rims and pads could be to blame, especially as the test ride started with a 5km fast descent, so the brakes were instantly put into service. Performance in the brief wet sections we hit was impressive, improving on the already high benchmark set by the likes of Zipp and ENVE.

We'll be spending more time on the 40 Cs in due course, but first impressions are good.

For more information see www.mavic.com.

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