Carbon wheel question

MJS996

Hi
First post here, be gentle with me! Apologies if this has been asked before.

I've read plenty that carbon clinchers are not great for descending, particularly if you're not a great descender and tend to use the brakes a lot. I've read it's about heat build-up resulting in increased pressure in the tube, and hence blow-outs etc.

Question is - do carbon wheels specifically designed for tubeless tyres have the same problem, given there is no tube and the opportunity for lower pressures? I know tubs are ok, just wondered if tubeless solves the problem as well?

Thanks
Martin

cycleclinic

Tube or no tube carbon clincher will all suffer if the heat build is high enough. Tubeless will help in that there is no tube to burst and it will be more difficult for the tyre to blow off but the rim can still fail due to heat as the tyre is still trying to push the rim apart, however use wide tubeless tyres at low pressures 60 or 70 psi then that will go a long way to help.

fenix

Where are you riding ? Most people are talking about descents in the Alps - we dont have many descents that can match it here.

trek_dan

The biggest risk is melting the rim not bursting the tube, I don't think going tubeless will make any difference.

northpole

Mavic make great claims for their C40 wheels which have carbon finish to all visible surfaces and an aluminium core which in part is meant to address heat problems. Suggest you view their web site.

Bigger issue for me with carbon rims would be rain and long descents.

Peter

MJS996

Thanks for the advice.

Descents I am thinking about are in the Alps and Pyrenees, and most notably Ventoux which I found the scariest descent of all - most of the Alps didn't seem too bad!

I may only go once per year, and even then not every year, but I don't want to spend a lot of money on wheels then not be able to use them on the best trip of the year!

I think I'll stick with aluminium rims - no desire to go down the tubs route

Thanks
Martin

nicklong

Alu-carbon rims can fix that issue. Look at Shimano c35 / c50s, Fulcrum Red Winds, HED Jets etc.

You pay a 100g penalty at each rim.

antsmithmk

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19737277#p19737277]MJS996[/url] wrote:

Thanks for the advice.

Descents I am thinking about are in the Alps and Pyrenees, and most notably Ventoux which I found the scariest descent of all - most of the Alps didn't seem too bad!

I may only go once per year, and even then not every year, but I don't want to spend a lot of money on wheels then not be able to use them on the best trip of the year!

I think I'll stick with aluminium rims - no desire to go down the tubs route

Thanks
Martin

A decent set of aluminium wheels is what you want. Deep section carbon wheels are not that light... which is what you want going uphill.

MJS996

[url=http://www.bikeradar.com/forums/viewtopic.php?p=19738110#p19738110]nicklong[/url] wrote:

Alu-carbon rims can fix that issue. Look at Shimano c35 / c50s, Fulcrum Red Winds, HED Jets etc.

You pay a 100g penalty at each rim.

I really like the Shimano C35 - ticks pretty much all the boxes for me, but they're not tubeless compatible, and I have a hunch that is where the future lies (witnessed a great demo from Schwalbe at the bike show), so buying wheels which don't support tubeless tyres seems like buying something which is already obsolete.

Now - if Shimano produced a DuraAce C35TL....

cycleclinic

If you have 1600g or 1700g carbon wheels and try riding up Ventoux and replace with campagnolo zonda's for example or Shamal, how much time do you think saving 200 to 300g will save. On that kind of climb it is seconds at best.

The point about tubeless carbon wheels is that while the rim still gets hot it is the high pressure from a tubed tyre that cause the rim to fail. Given the lower pressures in a tubeless setup try 60 psi on 25mm tyres on a wide rim (they will spread to 27mm) then rim will have to get hotter for it to fail under that pressure.

That said I prefer alloy rimmed wheels when doing proper mountains or tubs. Carbon tubular wheels don't have a tyre trying to blow the rim apart. Carbon tubular wheels are also light, light enough that the time savings might be a hit more real depending on the wheels you are used to.

964cup

There's already a long thread on this topic on here.

Short answer: neither tubed nor tubeless pure carbon clinchers are truly appropriate for Alpine descending. Either get an alloy rim, or a hybrid, like the Mavic or Shimano variants. Note that just because tubeless can run with lower pressure doesn't mean you'd want to - you still need the correct pressure to get the right (roughly 15%) "squish" for your weight. Too low a pressure will slow you down and affect the bike's handling when descending. Note that also, although pressure is an issue in CFRP rim failure, it's really the rim reaching its glass transition temperature (a property of the resin), at which point the rim softens. All sorts of different stresses, including tyre retention pressure, can then cause it to fail.

If you want a tubeless setup that's appropriate for Alpine climbs, try Shimano C24TL or Fulcrum Racing 1 or Zero two-way fit. Deep sections won't make any difference to your performance in the mountains, apart from potentially slowing you down with the extra weight. Or get a handbuilt wheelset; Stans Alpha 340s can come in at around 1350g in a mid-price (£450-ish) build, with Pacenti SL23s about 100g heavier. Both of these will be much cheaper to service than either the Shimanos or the Fulcrums. The Fulcrums are notably horrible to work on, speaking from experience.