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The Torqued Wrench: Taking on the carbon clincher

  • By Caley Fretz
  • Published Mar. 13, 2013
Carbon clinchers have pitted aerodynamics, ease of use, and vanity against weight and safety. Mavic may be onto something new, however. Photo: Loris Von Siebenthal | Mavic

NICE, France (VN) — Its benefits are often questioned, its place in the industry is contentious, and its consumer value is suspect. It could even be flat out dangerous, failing where other products have no problems.

It is the carbon clincher and, despite all of this, we have seen a steady increase in its presence, a whirring proliferation through group rides and races and everyday lunch loops that shows no signs of slowing.

But why?

Certainly it’s not weight. Carbon clinchers are usually upwards of 200 grams heavier than their tubular counterparts, for a comparable rim — Zipp’s 303 Firecrest tubulars come in around 1250g and the lightest 303 Firecrest Carbon Clincher we’ve weighed tipped the scales at 1473g.

The lightest carbon clinchers, wheels like Reynolds’ MV32c and Zipp’s new 202 Firecrest CC, rarely break 1350g. Each of the aforementioned would be lucky to get within 50g of that mark. Invariably, they hold price tags over two grand, $2250 for the former and $2700 for the latter. A set of aluminum Mavic Kryrium SLRs weighs just a bit more at 1419g and costs about half of a set of Zipps: $1400. A set of aluminum NoTubes Alpha 340 wheels weighs 1326g and is only $1000. At these low wheel depths, the aerodynamic drag difference between each of these wheels is tiny.

So consumers aren’t after weight, apparently, and are certainly not looking to save a few bucks. Perhaps it’s the braking?

Hilarity! No, it’s not the braking they are after.

Every current carbon clincher has gravely (in the literal sense of the word) serious problems with heat management. Even if they rarely reach the glass transition (melting) points of their resins, an event that causes the sidewalls to warp outwards with predictably explosive results, they still generate massive localized heat figures, upwards of 400 degrees Fahrenheit — so hot that manufacturers don’t recommend using latex tubes because they’ll explode.

With full-carbon construction, the heat problems are unavoidable. At least for now, nobody has figured out how to make carbon fiber transfer heat like a metal. Rather than spread throughout the rim, much of it ends up transferred into the tire and tube. That raises the PSI inside the tire, further compounding the aforementioned explosion problems. And, even if the tire stays seated, that higher pressure — we’ve measured increases of 30 psi after a hard stop — decreases grip in the very corner you just slammed on the brakes for. Double trouble.

On top of this, carbon brake tracks are universally awful when put up against a good, machined aluminum track. They have improved dramatically, but still aren’t quite there. In the wet, even the best require a full wheel rotation, allowing the pads to wipe the water off, before any real power can be applied.

So, again, why? Heavy, expensive, potentially explosive, and unable to stop in the rain. That’s not exactly a sexy PR line.

But carbon clinchers do have three main points in their favor. The first is ease of use, the second is aerodynamics, and the third is vanity.

The first point of favor is self-explanatory. Carbon clinchers are… clinchers. No glue. Little more needs to be said.

Point two is relatively simple as well. It is very difficult to extrude deep aluminum rims, and they are always heavy. Carbon clinchers are available in depths above 50mm, and it is at these depths that aerodynamics can make a real and even noticeable difference at high speeds. These deeper carbon clincher wheels are significantly lighter than both the hybrid carbon/aluminum sets currently available and the attempts at deep, all-aluminum wheels. Plus, the shape of a carbon rim can be exquisitely tuned to improve aerodynamics and crosswind control.

If you want an aerodynamic wheelset and don’t want to ride tubulars, carbon clinchers are an option. That is assuming, of course, that the heat and braking issues don’t bother you.

Point three is a little touchier with many in the carbon clincher-buying crowd.

My bike looks good. Really good. It’s custom Ti, with couplers for travel and a silky shot-peened finish with polished details. It looks nice with almost any wheels, I think. But throw a set of medium-depth, deadly dark carbon hoops on and it comes to life. It goes from good to gorgeous.

My bike is not alone in this particular attribute. Deep wheels, with most bikes, look better. Dark and deep wheels are better for material sex appeal than aluminum hoops; they’re a step up on the hybrid carbon/aluminum options, too. That shiny brake track just doesn’t work.

It’s not a huge leap, then, to believe that the sort of individual who can afford to spend a few thousand dollars on bicycle wheels may be taking the visual into account. I would venture that it’s a major reason for the growing popularity of carbon clinchers — because, as you’ve just read, most of the time they do not perform any better than an aluminum counterpart. Often they’re worse.

Three benefits, then, to a long list of drawbacks. Drawbacks that not only hinder performance, but can actually be dangerous. Drawbacks that add tire pressure in corners, prevent the rider from slowing down in the rain, and could potentially cause the wheels to explode from underneath the rider — however unlikely that is these days. A lot of drawbacks, few gains.

It is not surprising, then, that companies continue to seek alternative solutions. From brake track treatments to metal threads to aid in heat dispersion, they poke and prod and investigate. The research and development has helped carbon clinchers go from universally frightening to largely acceptable — but they’re still far from perfect.

Why this column, today? Because in a few hours a story from Mavic’s recent press launch in Nice, France, will run on VeloNews.com, and I think the French company may have found a model that eliminates some of the truly scary side effects while maintaining acceptable performance. The new Mavics still aren’t perfect, but they are at the very least inventive. To discuss a possible solution, first the problems need to be understood.

FILED UNDER: The Torqued Wrench TAGS: /

Caley Fretz

Caley Fretz

Tech Editor Caley Fretz can usually be found chasing races along the backroads of Europe or testing bikes and gear in the mountains outside Boulder, Colorado. If you can't find him there, check the coffee shop across from VN World Headquarters.

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