Mavic Cosmic Pro Carbon SL C wheelset

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.

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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.

> Check out our guide to road bike wheels here

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.

Verdict

Lightweight and fast full-carbon clinchers with excellent braking in both wet and dry conditions