Carbon Wheels

[moose12]

Hi there , please could someone  explain what the advantage of carbon wheels are if any ?

 

Why would you choose a carbon clincher to a normal aluminium ?

 

[Larry]

They are usually lighter

[Christie]

The main advantage is in aerodynamics. Aero wheels will save you in the region of 1 to 2 minutes over a 40km time trial. They will also save you energy if you go on solo attacks, breaks, or if you ride a lot at the front of the bunch in a road race. (If you suck wheel in the bunch most of the time, like what I do when I race elite, deep sections is a waste of money)

The other reason is for looks.

Lower mass won't make much difference, the races in South Africa is too flat.

 

 

[turtlek]

lighter, sexier, apparently faster.... its all in the mind!!!

[davidtinker]

Not just lighter but less weight on the rim -> less weight to spin up -> quicker acceleration. Deep section carbon wheels may also be stiffer as the spokes are shorter.

[Johan Bornman]

Not just lighter but less weight on the rim -> less weight to spin up -> quicker acceleration. Deep section carbon wheels may also be stiffer as the spokes are shorter.

 

Dave, this tenatious myth was busted here just before you joined. Search for rotating weight and you'll come across a long argument explaining why this is a myth.

 

As for stiffness, carbon wheels are stiffer but not because of shorter spokes but because the material is stiffer and there is more of it.

 

For a long or short spoke, for a given mass attached to it, it'll elongate the same amount. Therefore from a spoke deflection point of view, both are equally stiff.

 

Carbon is the preferred material for making deep section wheels. Aluminium in these volumes is just too heavy. Deep section carbon wheels thus have a weight advantage over deep section alu wheels but that advantage diminishes as the section becomes shallower and shallower, to the point where the best material for a box section rim is aluminium.

 

 

[Christie]

Not just lighter but less weight on the rim -> less weight to spin up -> quicker acceleration. 

 

I agree with JB. Your statement is correct in an academic sense, but accelerations in a bike race are fairly small. If you look at a graph of speed (logged by polar etc) during a road race, the changes in slope (acceleration) is fairly gentle.

Christie2009-06-14 11:57:12

[Jon0]

i find they make a diffrence =) keep on spinning....2,3 km for free....

[buckstopper]

Christie, if you look at a course like Junior Worlds in Moscow (on th UCI site) there are some 50 significant turns per lap of 13km - boys about 10 laps and girls about 6. For the guys, assuming there is a fairly significant acceleration, 500w+ out of each corner for 10 laps, thats a lot of accelerating. Weight saving must surely be an issue here.

[Christie]

On a course like what you describe, buckstopper, perhaps there will be a small benefit. I say a small benefit, because the speed will drop to 25km/h through the corner, then go up to 40km/h after that - that is not a big acceleration as far as physics go. But granted, at that level, any small benefit is probably worthwhile.

In SA, very few races are like that. Not a lot of criteriums or lap races over here.  

[1kTT]

Hi John,

 

 

 

I agree that carbon's advantage reduces as the profile of the rim reduces but   I am surprised that you say that at some point an ali rim will be the best material. Could you give an example ?

 

 

 

How do you factor in the superior design and construction techniques that are only available for carbon wheels ?

 

 

 

Finally are you saying that a carbon spoke is the same stiffness as an ali or steel one for the same length ?

 

 

 

 

[flex]

Deep section carbons just look SOOOO good

[Johan Bornman]

Hi John' date='

I agree that carbon's advantage reduces as the profile of the rim reduces but   I am surprised that you say that at some point an ali rim will be the best material. Could you give an example ?

How do you factor in the superior design and construction techniques that are only available for carbon wheels ?

Finally are you saying that a carbon spoke is the same stiffness as an ali or steel one for the same length ?

[/quote']

 

Carbon brake tracks are notoriously poor brakers. You need special pads and then still suffer performance, hence the inclusion of an aluminium brake strip in good carbon clinchers. At some point the vestigal piece of carbon becomes senseless. Some people will disagree with me on braking performance and say that good enough is good enough. They're right too, I suppose and we'll differ there.

 

However, if you look at a good carbon deep section that's both light and strong (most of the cheaper ones are heavy and strong, just like alu), you'll see that the spoke bed is a solid piece of carbon and the deep section walls very thin strips of carbon, soft enough to press in with your finger. The tubby bed is once again a thick substantial piece of carbon.

 

The weight saving here is only in the sidewalls, not in the spokebed and tubby bed. These two pieces have to be thick and strong, the tubby bed for inward compressive forces from inflation and the spoke bed from inwards tensile forces from spoke pull.

 

As the section gets shallower and shallower the weight saving area gets smaller and smaller until, at a point roughly what looks like an Open Pro box section, the entire rim is thick carbon and resin and weighs exactly what an alu rim would weigh. At a tenth of the cost, you may as well then have an alu rim.

 

 

[1kTT]

 

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However' date=' if you look at a good carbon deep section that's both light and strong (most of the cheaper ones are heavy and strong, just like alu), you'll see that the spoke bed is a solid piece of carbon and the deep section walls very thin strips of carbon, soft enough to press in with your finger. The tubby bed is once again a thick substantial piece of carbon.

 

?

 

The weight saving here is only in the sidewalls, not in the spokebed and tubby bed. These two pieces have to be thick and strong, the tubby bed for inward compressive forces from inflation and the spoke bed from inwards tensile forces from spoke pull.

 

?

 

As the section gets shallower and shallower the weight saving area gets smaller and smaller until, at a point roughly what looks like an Open Pro box section, the entire rim is thick carbon and resin and weighs exactly what an alu rim would weigh. At a tenth of the cost, you may as well then have an alu rim.

 

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[/quote']

 

 

 

Hi John,

 

 

 

I think you should be careful about generalizations here.

 

 

 

Not all carbon rims are created equal and what you have described certainly applies to rims like Zipps. Others like Lightweights use different construction techniques where spokes, hubs and rims are a single integrated unit. In this case, their lightest rims are also their low profile ones and at 950g for a set are substantially lighter than any ali wheelset that i have seen that is robust enough to be ridable on a daily basis and doesn't carry a ridiculous weight limit.

 

 

 

I do agree with you on price- Carbon rims, especially the exotic ones re substantially more expensive than ali.