Carbon wheels for descending?
piersj01
Posts: 32
Hello,
I'm looking to buy a set of Zipp 202 Firecrest carbon clinchers with a powertap hub and will use them for the all my riding on various different events including the Maratona and Marmotte. I'm not a brilliant descender but don't drag my brakes the whole way down.
Do you think these wheels are now safe for long alpine type descents?
Amy thoughts really appreciated.
Thanks,
I'm looking to buy a set of Zipp 202 Firecrest carbon clinchers with a powertap hub and will use them for the all my riding on various different events including the Maratona and Marmotte. I'm not a brilliant descender but don't drag my brakes the whole way down.
Do you think these wheels are now safe for long alpine type descents?
Amy thoughts really appreciated.
Thanks,
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Comments
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By that do you mean is it now ok to drag your brakes because the wheels put up with it a bit better?0
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Read what Wheelsmith have to say re carbon wheels.M.Rushton0
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No. Tubulars or alu clinchers for Alpine descents.English Cycles V3 | Cervelo P5 | Cervelo T4 | Trek Domane Koppenberg0
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Thanks. What about if you have a carbon clincher rear wheel (because of the Powertap hub that you have in it , like a zipp 202) but change the front wheel for an aluminium clincher just for big alpine events, as the front takes most of the braking force?0
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No.English Cycles V3 | Cervelo P5 | Cervelo T4 | Trek Domane Koppenberg0
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Don't see the point of 202 clinchers. They're 1450g. I could build you a set of alloy clinchers that weigh the same for less than £400. There are endless factory alloy choices at around that weight, too, again for less money.0
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If weight is a concern then Tune Mig/Mags on Pacenti SL25's. If you want something that will last forever go with DA9000 hubs.English Cycles V3 | Cervelo P5 | Cervelo T4 | Trek Domane Koppenberg0
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I did the Maratona last year and there is no way I would ever recommend carbon rims for that terrain/ event.
There were quite a few extremely ill-disciplined riders (amongst the many decent riders) who were quite happy to zip by and cut others up on approaches to bends - extremely good brakes needed in such circumstances.
On the final significant climb and descent the rain came on quite heavy - this is the very last situation you want to have carbon rims fitted. In the mountains, the weather can change very quickly and you only have one set of wheels with you. My advice is to make sure they are alloy rimmed, not carbon. Please note, I apply alot more pressure on the rear rim braking than I imagined. I did try a combo of Zipp 303 firecrest rear and DA C35 front following the same logic the OP expressed - very enjoyable, in the dry!
Peter0 -
Don't see the point of 202 clinchers. They're 1450g. I could build you a set of alloy clinchers that weigh the same for less than £400. There are endless factory alloy choices at around that weight, too, again for less money.
Indeed. I built a pair of wheels that weigh 100g less than that and that cost me £200. OK, light rider in dry weather only but I guess most people would be keeping their 202s out of the rain!Faster than a tent.......0 -
http://www.bikeradar.com/forums/viewtopic.php?f=40091&t=13037993
What's wrong with using the r-sys you are selling by the way? You said "I am selling as I rarely use" and yet you're looking for more wheels?0 -
Basically selling three pairs of wheels (haven't posted the others yet) and selling Garmin Vector pedals as well with a view to buying one set of wheels with a powertap rear hub, which I can't do with the R-SYS. That's why I was considering Zipp 202s.0
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What about a powertap crankset instead - then the world's your lobster as far as wheels are concerned
For the price of the Zipp's you could have a powertap crankset and plenty of change for some decent wheels0 -
I agree with everyone else here. Carbon rims are not good for big descents- hell I don't even use mine in North Wales! Apart from crap braking, especially in the wet, carbon composite doesn't dissipate heat as well as alloy and you see a lot of cyclists on the first descent of the likes of the Marmotte who have cooked their rims and tubes and punctured. One of the big advantages of disk brakes I think will be being able to have fancy carbon rims but with proper braking. If you must go Powertap then get it built into a good set of alloys. Personally I'd rather have a crank based power meter and be able to swap wheels as I wished.0
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I don't understand the appeal of shallow carbon clincher wheels. They're not that much lighter than their alu counterparts and have quite a big drawback. You already have everything you need, so why sell all your stuff to buy overpriced wheels that don't have any advantages over your current kit?English Cycles V3 | Cervelo P5 | Cervelo T4 | Trek Domane Koppenberg0
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I used Bora 35s clinchers on mountain descents and they were fine. It was dry thoughPegoretti
Colnago
Cervelo
Campagnolo0 -
Now I really don't understand. You already have power-metering pedals and light-weight wheels. What is the benefit of 202s with a PowerTap, apart from adding 350g to your bike? I mean I'm all for pointless expenditure on bike bling, but surely you'd want it to constitute an improvement, even if only when calculated using man-maths? If you really need carbon rims, do it properly and go tubular. 202 tubs are 1180g the pair (claimed). Wouldn't be my first choice - I'd go with Enve 45s on Chris King (in fact, I did), but at least there'd be some logic. If you want a power-meter that moves easily between bikes, then sure - get them built on a PowerTap, but remember the G3 is hardly the lightest hub out there. By the time you've finished your current plan, I'm sure it would have been cheaper to buy a metered crank for all of the relevant bikes. I'm using Rotor Power LT in both of my "proper" bikes - about £650 out of Germany at the moment, stiff as a stiff thing and still very light.0
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It's not the rain, although that matters - it's the risk with clinchers of heating the rim past the glass transition temperature, at which point the CFRP softens and the rim can fail. The reason people recommend tubs instead of clinchers is that the rim of a tub is under no lateral stress, whereas a clincher is constantly holding back the pressure in the tube (which will increase as heat from the rim transfers to the air in the tube). Manufacturers are making continual progress in dealing with this, either by (ironically) adding alloy reinforcement to the rim (Mavic) or by innovating new braking surfaces and pad materials, but the fact remains that the rim of a carbon clincher is being asked to do three jobs at the same time (wheel, brake and pressure vessel) where a tub only has to do two.I used Bora 35s clinchers on mountain descents and they were fine. It was dry though0 -
I thought campag had overcome all that which is why its taken them so long to launch them? I also have Bora 50 tubs which are much nicer to ride on but dont brake as well and are lethal when wet.
It's not the rain, although that matters - it's the risk with clinchers of heating the rim past the glass transition temperature, at which point the CFRP softens and the rim can fail. The reason people recommend tubs instead of clinchers is that the rim of a tub is under no lateral stress, whereas a clincher is constantly holding back the pressure in the tube (which will increase as heat from the rim transfers to the air in the tube). Manufacturers are making continual progress in dealing with this, either by (ironically) adding alloy reinforcement to the rim (Mavic) or by innovating new braking surfaces and pad materials, but the fact remains that the rim of a carbon clincher is being asked to do three jobs at the same time (wheel, brake and pressure vessel) where a tub only has to do two.I used Bora 35s clinchers on mountain descents and they were fine. It was dry thoughPegoretti
Colnago
Cervelo
Campagnolo0 -
The latest Giant climbing wheels are lighter than the Zipps and have a higher temperature rating.0
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I went to the Pyrenees in September with Bora One 35 clinchers and survived.
I was a bit worried based on all the horror stories I'd read, but I had no issues descending all the big Cols there. If anything, heat buildup was more of an issue on the descents of the shorter/steeper Cat4 and Cat3s. Campag assured me their new rim technology was safe providing you don't drag the brakes and are a "pro racer".
For reference, this was in the dry with rider weight of 60kg and first time in the mountains so not exactly Peter Sagan descending skills.0 -
You can comfortably get down an alpine descent on carbon clinchers and have no issues, but the margin for error is significantly reduced against a set of alu wheels for the reasons everyone has mentioned. I've had a fantastic descent down one side of the stelvio where brakes were hardly touched, the next day I had a hairy descent down the Mortirolo where I was glad on I was my C24's. The difference was the consistent stream of motorbikes and sports cars who had all decided to have a rally up the mountain, at one point I actually stopped to check the heat on my wheels after heavy braking on pretty much every bend to avoid traffic swinging wide on the way up.
The point is that you can't control all of the elements that will influence your ride, and halfway up a mountain isn't a great place to have an issue. So ride something that gives you the broadest margin for error, be that wet weather braking or heat dissipation. Not least as you don't actually need the aero advantage that Zipp wheels were designed for in the mountains.0 -
Agree with all of that. Weight is also a factor. Shamrock is 60kg. I'm 78kg at my lightest; 80kg on average - so 33% heavier. That puts a lot more energy through the brakes, thus generating a lot more heat. There's a also a risk in saying "Alpine descents" as if they're all the same. Croix de Fer to St Jean de Maurienne, which apart from the first bit is long and sweeping, is quite different to Alpe d'Huez, for instance - the famed 21 hairpins of the latter take a lot more out of the brakes. By the same token, you wouldn't want to be a cautious descender coming back down into the river valley from Croix de Fer if you didn't absolutely have faith in your brakes (it's very steep, very very fast and then there's a tight right hander at the bottom).0
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This is super awesome!no matter what the problem would be resolved, we will become more and more popular bars!I used Bora 35s clinchers on mountain descents and they were fine. It was dry though
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Wut? :shock:English Cycles V3 | Cervelo P5 | Cervelo T4 | Trek Domane Koppenberg0 -
Go to a disc equipped bike!0
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best thing to do is get as Grill and others say, some ightweight alloy clinchers. pacenti sl23 hoops are good for this. if your budget goes to it, go for tubs if you are doing nice alpine climbs. dura ace hubs, for year round reliability. Job done.0
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It's not the rain, although that matters - it's the risk with clinchers of heating the rim past the glass transition temperature, at which point the CFRP softens and the rim can fail.
Very unlikely. Most carbon composite uses thermoset polymer matrix so it doesn't have a glass transition.0 -
Odd then that the industry is full of stories about this. Here are quotes from Zipp & Reynolds on the subject:It's not the rain, although that matters - it's the risk with clinchers of heating the rim past the glass transition temperature, at which point the CFRP softens and the rim can fail.
Very unlikely. Most carbon composite uses thermoset polymer matrix so it doesn't have a glass transition.Two words: glass transition (Tg). Tg is the temperature at which the epoxy begins to deteriorate. In the case of clinchers, when the epoxy reaches Tg the outward pressure of the tire and tube can cause the rim’s sidewall to deform, potentially resulting in a catastrophic failure.
On a long descent, braking temperatures can reach 300 degrees Fahrenheit; resins not designed for high heat will reach their Tg point well below that, resulting in rim failure. Raising the Tg point of the resin is the obvious answer, and one that carbon clincher makers have been trying to perfect for years.
When talking about Zipp’s resin woes in developing their carbon clincher rims, Josh Poertner states, ‘The thing we had the hardest time with was finding the right resin to use. High-temp resins are usually not tough enough, while highly toughened resins make great handlebars but can’t necessarily handle high temperatures. What you dope the resin with to get one feature comes out at the expense of the other feature. We sat down with nearly every resin vendor around the world and said we need both A and B. We finally found a small vendor that specializes in Formula One racing who was able to provide the specs we needed.’
While the resin development has evolved to allow for a higher Tg temperature, brake pad technology has evolved too. ‘We developed a polymer brake pad in conjunction with a polymer brake track. Together they lower the braking temperature by 100 degrees Fahrenheit,’ said Lew of Reynolds.
From: http://roadbikeaction.com/features/rba-features/tech-report-the-real-story-behind-carbon-clinchers. Google produces 2,530 results for "carbon clincher glass transition temperature".0 -
I stand corrected. Long time since I did any polymer chemistry. Epoxy won't melt and flow like polythene because its crosslinked but it does look like it will soften enough to cause issues.0
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I got down Monte Grappa on a pair of Miche SWR RC carbon clinchers. There's a fair few hairpins on the particular descent I went down.
If you choose some premium quality carbon clinchers, fit some Swiss Stop Black Prince pads and have good technique then you'll be fine.
Braking quality and durability has come a long way. Miche spent years developing their rim to withstand hard braking0 -
I got down Monte Grappa on a pair of Miche SWR RC carbon clinchers. There's a fair few hairpins on the particular descent I went down.
If you choose some premium quality carbon clinchers, fit some Swiss Stop Black Prince pads and have good technique then you'll be fine.
Braking quality and durability has come a long way. Miche spent years developing their rim to withstand hard braking
Would that commentary be equally valid in the wet? Black Prince are next on my shopping list, but I'd be hard to convince carbon works on long wet descents. Interested to hear if you found them ok in those conditions.
Peter0
