Carbon Rims
Comments
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Might be something to do with the heat they generate under heavy braking. Not good for alpine descents on hot days. Can cause the tyres to pop.0
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I don't think that he does as it happens, not that I would buy one even if they came with a power bar made out of fried gold.
He is right though, a bit of damp or anything else and you do have problems with carbon rims. There are intrinsic risks to carbon rims, you often see riders on mountain stages with a rear carbon rim and a front alloy one...this pretty much mitigates the risk, if not negates it...Geraint was on all carbon...0 -
this is what confuses me... I thought carbon rims were less effective than alloy ones in terms of braking force, most of the accidents looked like they were caused by the wheel locking up...
i personally like the idea of carbon rims, i am currently looking at getting some myself :PFCN: 5/6 Fixed Gear (quite rapid) in normal clothes and clips
Cannondale CAAD9 / Mongoose Maurice (heavily modified)0 -
anonymousforobviousreason wrote:Iyou often see riders on mountain stages with a rear carbon rim and a front alloy one...this pretty much mitigates the risk, if not negates it...
That's usually when they get a flat and have to get a wheel from neutral service 8)0 -
Skippy2309 wrote:this is what confuses me... I thought carbon rims were less effective than alloy ones in terms of braking force, most of the accidents looked like they were caused by the wheel locking up...
i personally like the idea of carbon rims, i am currently looking at getting some myself :P
I ride Lightweights (yes lucky me)...and have had a fair few "freaky" moments...brake pads are changed once every couple of weeks minimum...
I also ride fixed a lot so am very used to thinking that much further ahead with regard to stopping....if your knees are up to it then (yes I know it has been said a gazillion times) no brakes experience makes one think differently even when one has them....
Fixies are cheap and a lot of fun but they also teach you a lot, during the winter and bombing around town on a fixie isn't a bad way to learn how to focus a little further ahead when thinking about stopping...which is what is needed with carbon rims, slam them and you will lock up....0 -
I don't normally ride carbon rims but on the occasions I have I've noticed that the brake pads can "stick" to the rim under heavy breaking. Feathering the brakes usually prevents this, but if you ahve to brake hard and suddenly, I think it could easily have you off...Head Hands Heart Lungs Legs0
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I think Chris Boardman has been listening to Richard Virenque and Jackie Durand. What Virenque said when GT crashed (or screamed really!) was "change your wheels!" and he kept screaming it all the way down the col until he noticed that GT had done so. Same comment today for Jens Voight (and it is a comment that has been made a lot of times since the beginning of the Tour).
There are two problems. One is the brutality of the braking effort on carbon rims which tends to catch people out in the wet (even with the right blocks). It did my neighbour with his carbon wheels out training and it is a known problem. He was warned about it and the same comment has been made several times since the beginning of the Tour (all those damp stages).
The second problem is that of a very rigid wheel skipping on the rough road surfaces at altitude (and elsewhere). Tyre pressures also play a part. Thomas Voeckler changed bikes (yesterday I think, not the Tourmalet stage) because his tyre pressures were too hard and he couldn't control the bike on the descents (second thought, it must have been the Tourmalet stage, I have a vivd memory of him stopping next to a camping-car but can't remember which stage)0 -
Because of the way carbon rims are made, it's almost impossible to get the finish/tolerance of the braking surface and so they tend to be a bit 'grabby' and therefore braking can be harder to regulate and at times it's easy to overcook it. The stiffness of the rim can be difficult on a rippled surface - the wheel hops and skips. Pros ride tubulars so the issues about overheating and punctures is irrelevant. Carbon rims in heavy rain can be really 'interesting' often with brakes having little effect which makes corners and descents a challenge at high speed - I've had times going into bends where I wasn't sure I'd get round.Make mine an Italian, with Campagnolo on the side..0
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Monty Dog wrote:Because of the way carbon rims are made, it's almost impossible to get the finish/tolerance of the braking surface and so they tend to be a bit 'grabby' and therefore braking can be harder to regulate and at times it's easy to overcook it. The stiffness of the rim can be difficult on a rippled surface - the wheel hops and skips. Pros ride tubulars so the issues about overheating and punctures is irrelevant. Carbon rims in heavy rain can be really 'interesting' often with brakes having little effect which makes corners and descents a challenge at high speed - I've had times going into bends where I wasn't sure I'd get round.
So why use them on mountain stages? Genuine question- sounds like some pretty serious disadvantages to them, do the advantages outweigh them that much?0 -
The aero and weight benefits do make life easier in the mountains or at high speed but I guess it also comes down to what the team / sponsors provide and rider preference. The other problem is that you can't change brake pads mid-ride so unless you swap bikes - not an option available to domestiques, then having a carbon brake pad with an alloy rim can also be sub-optimal.Make mine an Italian, with Campagnolo on the side..0
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Monty Dog wrote:The aero and weight benefits do make life easier in the mountains or at high speed but I guess it also comes down to what the team / sponsors provide and rider preference. The other problem is that you can't change brake pads mid-ride so unless you swap bikes - not an option available to domestiques, then having a carbon brake pad with an alloy rim can also be sub-optimal.
Agreed, but it's a risk. Falling off a mountain is also sub-optimal.....Head Hands Heart Lungs Legs0 -
maybe it's something for the UCI to look into. If they are causing problems maybe they should only be used on flat stages or TTs.0
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I work in the prosthetics industry and we use carbon fibre in many products. We engineer our feet and legs to store then release energy and carbon is excellent in this application, Note the amputee running on carbon blades during the ads. I wonder if carbon rims get loaded up on those tight hairpins and release the energy causing the rider to get spat off line?
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