rpenmanparker 

Supposing you incorporated a thin layer of aluminum foil between layers of the carbon prepreg layup when building a carbon rim, could significant heat be moved from the brake track down into the side walls of the rim and spread over more carbon mass to reduce the rise in temperature during hard braking. Of course the foil would have to be perforated to allow the CF layers sandwiching it to bond to each other and maintain the strength and integrity of the structure. And you wouldn't want to move too much heat down to the area near the spoke holes. Softening them could be disastrous. Just wondering.

wphamilton

I'm worried about this part - basically a layer of tin foil sounds like a structural flaw. But the concept is interesting and I love novel ideas. What about a hybrid type of composite? I did find this, googling around, Revolutionary aluminum composite stronger and lighter than carbon fiber, alternating layers, which seems to be almost the same as your idea.

PiLigand

I like this. I would suggest filaments rather than layers of foil for the same concern of connecting layers. Definitely an interesting idea. Could be especially effective on deep wheels.

Consider, though, that better heat dissipation could be achieved on deeper wheels while those braking often are usually doing so on hills and therefore less likely to have appreciably deep wheels?

PiLigand

Neat. Although:
As I understand, metal matrices (and I assume these metal layers) are going to be technically stronger but also more flexible than straight carbon composites. this is probably good for airplanes, but bad for bikes.

rpenmanparker 

Yes, I am concerned about the structural integrity and stiffness too. But the stiffness of aluminum is significant enough to make rims out of it along, so a thin layer should contribute reasonable stiffness to the whole structure proportionally to its thickness and weight. Not much stiffness added or subtracted, but very little aluminum used. The losses in stiffness and lightness should be minimal. As for the integrity, that is the purpose of the perforations, to let the prepreg bond through from one side of the aluminum to the other. In a way it is like rebar in concrete except the aluminum isn't being used for its strength but rather for its heat conductivity. You could say that rebar is a structural flaw in a road, but that is how composites work.

Good responses, thanks.

rpenmanparker 

Don't people who go for aero wheels ride them everywhere?

coachboyd

A couple things

It's very hard to bond anything to carbon, especially in between layers of carbon that are supposed to have structure. There have been lots of methods to trying this, from bonding carbon or a ceramic material, to using an aluminum rim bed wrapped in carbon. If the TG point of the resins is met, bad things happen. The Madfiber wheels that had an aluminum rim bed wrapped in carbon still had issues with delamination under hard braking. There are other cases where the ceramic coating will start flaking off and the heat still transfers through.

Brake pad development is currently one of the best ways to lower heat build up. It's amazing to see the difference in temperatures using different brake pads under the exact same conditions on the same wheels. There's differences of over 100 degrees Celsius using the exact same braking conditions.

Resins are getting better and better, they can withstand higher temps for prolonged periods of time. Most of the high temperature resins now can handle almost 200 degrees Celsius. With brake pads that help keep heat lower the temperatures are lower that this even with prolonged hard braking. The problem becomes with dragging the brakes there is heat constantly transferring to the tube and tire. This can raise the PSI to the point of causing blowouts, which is why braking in an on/off patter is good for building and dissipating heat.

There may be some new novel approaches, but the approach that is best working is the one that is currently in process. Good brake pads and good resins.

PiLigand

I mean, I do, but I thought I was a minority and that most hillier people liked low-profile lighter wheels.

rm -rf

You are too late!
I remembered a wheel with copper threads embedded in the carbon to dissipate heat. I googled, but didn't find it. Instead, this patent showed up.
Carbon fiber rim, bicycle including the same and manufacture method thereof

That patent really tries to cover anything related. I wonder if they've actually made one, or just want to get paid if anyone builds something similar.

~~~~~
But Reynolds claims that they use the carbon fiber itself to conduct heat away, and that their rims run cooler.

Wikipedia says that there's two kinds of carbon fibers. Interesting.I don't know which kind is used on wheels.

cale

The aluminum would have to have sufficient mass to do its job and this raises issues of overall weight. (Counterproductive in a design where the intent is to reduce mass.) The idea to incorporate a heat sink is sound but sandwiching carbon and aluminum, IMHO, will result in a weaker structure because it relies on the outer layer of carbon to transfer the heat. Ideally, it would make more sense to layer the aluminum on the outside where the efficient transfer of heat can occur.

rpenmanparker 

I don't dispute what you say, but you are ignoring the fact that the aluminum is not supposed to bond to the carbon. The carbon is supposed to bond to itself through the holes in the aluminum.

rpenmanparker 

Yes, but that would involve bonding problems as mentioned above. By sandwiching the aluminum you fix it in place with the carbon-resin-carbon bonds holding it firm through the perforations.

Also the aluminum only would have to add the weight difference between itself and the carbon composite. There would be a penalty, but very slight. The improvement in heat transfer is so great between aluminum and carbon that not a whole lot of aluminum would be needed.

rpenmanparker 

Hence the question mark after "novel" in the title of the thread. I suspected as much.

06SpiceRed

Yea if I recall MadFiber did a combination of these with their CCs like Boyd mentioned, but still had issues.

https://roadbikeaction.com/features/r...eel-comparison

Darth Steele

isn't Mavic doing something similar with their Carbon Clinchers?

wphamilton

if it turned out to be a problem, maybe you could weave aluminum fibers in with the carbon mesh or fabric.

cale

There's more than 1 way to bond carbon to itself and still maintain structural integrity. What sort of expansion allowances have been made?

Silvercivic27

Bro, that would add like 2 grams per rim. Not interested.

LansingWes

The future seems to be in graphene which is strong, light, flexible, and a good conductor. Graphene bicycles - the potential future of composites - BikeRadar USA

nhluhr

This just sounds a lot like what MadFiber and Mavic did with their not-quite-Full Carbon Clinchers.

grolby

Nothing quite like 41 armchair engineers.

rpenmanparker 

All good fun. What else do you have to post about, your junk showing through your shorts? Puhleeze!

UnfilteredDregs

You can't make a silk purse out of a sow's ear.

Dave Mayer

Enhancemnets to clinchers? No high-level riding is done on clinchers, so what is the point? Like putting a spoiler on a Pinto. Tubulars are far superior in heat dissipation, pinch flat prevention, the ability to run at higher or lower pressures, and safety in the event of a blowout. And the key insurmountable tubular (rim and tire) advantage: lower rotating mass.

UnfilteredDregs

So what happened to all those guys in Oman?