Mavic's new Cosmic Pro Carbon SL C wheels accelerate fast, hold their speed well, and offer excellent braking in both dry and wet conditions.
The Cosmic Pro Carbon SL C, like the new Ksyrium Pro Carbon SL C (£1,500), features all-carbon rims. Previously, Mavic used aluminium rim beds in its carbon clinchers for safety reasons – to dissipate heat – but the French brand believes that it has now developed a manufacturing process that allows it to dispense with the metal.
Mavic says it can now produce one-piece carbon rims that are consistent enough that they need no extra machining, which would weaken the structure, when they come out of the mould.
It has also developed a proprietary heat treatment protocol that increases the ability of the rim to cope with the high temperatures associated with prolonged braking. All of that means the aluminium insert is no longer necessary.
A laser process removes the resin from the surface of the brake track while leaving the carbon fibre intact, the idea being to ensure the best braking performance.
Let's start with the braking, then. It's excellent. With some carbon fibre wheels the braking is adequate, possibly reasonable, but not much more. With the SwissStop Flash Pro Yellow pads included, the braking on offer here is powerful. It's up there with the best carbon fibre braking in dry conditions, and it's a class apart from any other carbon fibre wheels I've ever used in the wet.
Braking on wet carbon fibre rims is notoriously unpredictable, but with the Cosmic Pro Carbon SL C wheels it's not all that much different from the dry weather performance. That's not an exaggeration; you'll be hugely surprised.
That consistency means that you don't find yourself wondering whether or not the pads will bite in wet and changeable conditions; you know that they will, and that gives you the confidence to leave your braking until you really need it rather than starting early to be on the safe side. Mavic really has set new standards here. That's especially good news if you happen to live on a rainy island like Britain.
Like most (but not all) of Mavic's existing Cosmic wheels, the Cosmic Pro Carbon SL Cs have 40mm deep rims, but these are a new rounded shape based on a NACA (National Advisory Committee for Aeronautics) profile.
The rims are wide – 25mm external, 17mm internal – so you might have to let out a bit of brake cable when you fit these. That's not as wide as Zipp's 303 Firecrest Carbon Clincher, for example (26.4mm across the brake track, 28.5mm maximum), but it's not far off. The idea is to integrate well with the wider tyres that most people are using now. Mavic recommends tyre widths from 25mm to 32mm.
The wheels are lightweight. We measured them at 601g (front) and 808g (rear) without skewers or tyres. Mavic claims a rim weight of 450g, but we're not going to disassemble them to check that. They accelerate snappily, especially for their depth, spinning up to speed fast when you want to get out of a corner quickly or jump away from other riders.
They hold their speed well too, and I didn't have any trouble at all with handling in crosswinds whatever speed I was riding. Even if you're a lighter rider, I can't imagine these being much of a handful.
The Cosmic Pro Carbon SL Cs don't flex much at all when you fling the bike about out of the saddle or corner hard, 18 straight-pull elliptical spokes at the front and 24 at the rear holding them firm. I certainly didn't feel the need to make any concessions through the bends thanks to the high level of precision.
The wheels incorporate the Instant Drive 360 freewheel system (Shimano/SRAM and Campagnolo options are available) that Mavic introduced last year. The design features a 40-tooth dual ratchet system that provides engagement in 9°. In other words, you start to drive the rear wheel almost immediately on resuming pedalling after coasting.
You get Mavic's own 25mm Yksion Pro GripLink (front) and PowerLink (rear) tyres as part of the package. I know some people don't rate Mavic options highly, but I've not had any issues here. They're not the stickiest choice out there in wet conditions, but I didn't find them especially slippy either. I'd probably replace them with something else when they wear out, but not as a matter of great urgency.
Overall, you're getting a great package here for a variety of terrains: plenty of speed and stiffness and an exceptional braking performance.
Lightweight and fast full-carbon clinchers with excellent braking in both wet and dry conditions
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road.cc test report
Make and model: Mavic Cosmic Pro Carbon SL C wheelset
Size tested: n/a
Tell us what the wheel is for, and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?
Mavic describes this as an 'Ultralight full-carbon clincher' wheelset with a 'superior aerodynamic performance' and 'best in class braking and reliability'.
It's designed as a high-performance wheelset, essentially for racing.
Tell us some more about the technical aspects of the wheel?
Mavic lists these features:
* The lowest inertia in the category
* Rim weighs just 450g, giving you instant acceleration
* 18 spokes on the front wheel and 24 on the rear, so you get increased lateral stiffness and optimal power transfer
* 40mm wind tunnel tested NACA profile rim
* 25mm external width (17mm internal) for perfect tyre integration and superior handling in all conditions
* iTgMax carbon technology for superior heat resistance and reliability
* The laser-treated brake track gives predictable braking in all weather conditions
* The unique single carbon layer rim bed wrapping is created without machining or fibre cuts
* Material: 3K carbon fibers
* Height: 40 mm
* Drilling: traditional
* Brake track: carbon with iTgMAX technology
* Valve hole diameter: 6.5 mm
* Tyre: clincher
* Internal width: 17 mm
* ETRTO size: 622x17C
* Material: steel
* Shape: straight pull, bladed, double butted
* Nipples: aluminum, ABS
* Count: front 18, rear 24
* Lacing: front radial, rear Isopulse
* Front and rear bodies: aluminium
* Axle material: aluminum
* Sealed cartridge bearings
* Freewheel: Instant Drive 360
* Yksion Pro GripLink (front) & PowerLink (rear)
* Front and Rear Tread: Single Compound
* Casing: 127 TPI
* Breaker: Front Kevlar, Rear polyamide
* Dimension: 25-622 (700x25c)
* Freewheel: Shimano/Sram or Campagnolo, convertible to XD-R with optional driver body
* Front axle: Quick Release only
* Rear axle: Quick Release only
I've given some info in the main body on Mavic's new construction technique for its all-carbon rim.
The wheels are as true now after several weeks of riding as they were out of the box. The only real sign of use is a slight yellow residue on the brake track from the pads.
The sealed cartridge bearings are running very smoothly.
They're lightweight and accelerate fast without any notable compromise to stiffness.
Zipp's 303 Firecrest Carbon Clincher (45mm deep rims) have a claimed weight of 1,625g.
The Bontrager Aeolus 3 D3 carbon clinchers that we reviewed were 1,479g, but the rims are a little shallower at 35mm.
Mavic claims weights of 645g (f) and 805g (r). Our scales said the wheels (without tyres, inner tubes or skewers) are 601g (quite a bit lower than Mavic's claim) and 808g (just a touch higher).
In that context, the weight of Mavic's Cosmic Pro Carbon SL C wheelset is very impressive.
Zipp 303 Firecrest Carbon Clincher: £1,680 RRP
Bontrager Aeolus 3 (35mm): £1,949.98 RRP
Bontrager Aeolus 5 (50mm): £1,949.98 RRP
Compared with its closest rivals (and that's the only fair comparison) the Cosmic Pro Carbon SL C looks very good value, especially considering that you get tyres and inner tubes as part of the package.
Did the wheels stay true? Any issues with spoke tension?
They've remained completely true throughout testing.
How easy did you find it to fit tyres?
I got the tyres off and on again without levers. It would have been easier with levers, of course, but you'll not struggle.
How did the wheel extras (eg skewers and rim tape) perform?
No complaints there. The SwissStop pads are very good too.
Tell us how the wheel performed overall when used for its designed purpose
This wheelset accelerates fast, holds its speed well, and the braking is first rate.
Tell us what you particularly liked about the wheel
The all-round performance is very high but one of the real highlights is the braking.
Tell us what you particularly disliked about the wheel
Although the tyres aren't bad, they're not as good as everything else here.
Did you enjoy using the wheel? Yes
Would you consider buying the wheel? Yes
Would you recommend the wheel to a friend? Yes
Use this box to explain your score
Clearly, £1,500 is a lot to spend on a pair of wheels – 'You could buy a whole bike for that,' etc – but these put in an exceptional performance and the RRP isn't as high as that of close rivals, especially when you consider that you get tyres, inner tubes and brake pads included.
About the tester
I usually ride: My best bike is:
I've been riding for: Over 20 years I ride: Most days I would class myself as: Expert
I regularly do the following types of riding: commuting, club rides, sportives, general fitness riding
Mat has worked for loads of bike magazines over 20+ years, and been editor of 220 Triathlon and Cycling Plus. He's been road.cc technical editor for eight years, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. We send him off around the world to get all the news from launches and shows too. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a past winner of the Cycling Media Award for Specialist Online Writer.