Carbon tubulars better than clinchers for dealing with brake track heat on descents?

[happycampyer]

This is a longstanding and well-known issue. Not sure if the video is still on their website, but a few years ago when Zipp redesigned their clincher rims to withstand greater braking heat, they made a video showing the heat effects of braking on carbon rims. My recollection is that, when they were doing R&D for the new rims, they tested pretty much every name-brand wheel available and all failed their test except one (I have heard indirectly from a source that I believe to be reliable that the wheel that passed was the Hyperon clincher, which makes sense since Hyperons are ridiculously strong rims).

Personally, the only carbon clincher wheels I would ride would be for disc brakes. All of my carbon wheels for rim brakes are tubulars.

[pdonk]

Raoul Luescher http://luescherteknik.com.au/ provides lots of insight on this topic both on his web site and with "carbon maven" on you tube.

https://www.youtube.com/watch?v=ET1jRVynOBA

[earlfoss]

I have both carbon tubulars (Zipp 303), and clinchers (Bontrager D3 Aeolus 5). They've both done what they're supposed to with no problems. I've taken the Bontragers down the gnarliest descents in the L.A. area, given them some heavy braking, and they're totally fine. I suppose it's possible that prolonged braking on looooonnnnngggggggg descents might be another story, but for 99.9% of the situations I've have them in, they'll do the job just fine.

[Mark McM]

Originally Posted by pdmtong

What is the sustained temperature and duration the brake track of a given CF clincher rim would need to heat to in order for it to fail? And how does that translate into rider weight pad pressure descent slope and speed? How is that affected by drag : pulse brake techniques?

The Alto Cycling carbon clincher rim brake heat test:

https://bikerumor.com/2017/12/08/alt...im-brake-test/


I believe this test was discussed on the forum last year.

[hobbanero]

the issue with a softening brake track leading to blowouts on carbon clinchers is well trodden....though at 180 pounds I have never had an issue on name brand carbon clinchers made in the last 5 years on any of the steep descents in the Bay Area.

I have seen someone with carbon tubies heat the rim enough to soften the glue and the tire rolled. That could have been a bad glue job.

Coming off Mt Diablo in the Haute Route event really confirmed for me though that disc brakes are awesome. My rim brakes were doing the job, but by the bottom were making a lot of noise and pulsing. I have been down the same 3500' descent on discs and they were consistently good all the way down.

Seems like if you live in a steep area you should skip past clincher v tubie and go straight to tubeless clincher discs.

[fogrider]

I've had good luck with Reynolds Blue pads...and they now have the "power" pads that they claim to be 33% better in the dry, and I'll say they are about that much better! They claim to keep the rims cooler...

[verticaldoug]

ZIPP claims they worked with a supplier for a newer heat resistant resin for their clincher rims. I have the 303s and with the new brake pads, I think these are great.

Although you can still get the old cork brakes if you want that nostalgic smell of burnt cork first thing in the morning ride.

[glepore]

No question its documented. The temperature at which you're at risk depends on the "transition temperature" of the epoxy used, which varies from manufacturer to manufacturer. Another factor is braking style-short sharp braking followed by cooling is much less likely than constant medium braking without "off" periods.

As mentioned earlier, tubulars don't have the force against the bead, so its not a problem in most instances. And you're less likely to melt the glue on a carbon rim for the same reason they deform at the brake track-carbon doesn't conduct heat well, thus less heat gets transmitted to the rim bed.

[Dave]

I've logged over 35,000 miles in the Colorado mountains and never had a problem with aluminum clincher rims. If I had rim issues, I'd switch to aluminum or disc brakes.

[Mark McM]

Originally Posted by fogrider

I've had good luck with Reynolds Blue pads...and they now have the "power" pads that they claim to be 33% better in the dry, and I'll say they are about that much better! They claim to keep the rims cooler...

How do they support the claim that these brake pads keep the rim cooler? Brakes convert kinetic energy (energy of motion) into heat. For the same amount of braking, the same amount of heat is generated. How much the heat raises the temperature will depend on the ability to dissipate the heat (i.e. conduct and convect the energy away). The brake pads won't change the ability of the rim to conduct/convect energy, so the only way that the pads can keep the rims cooler is if the pads themselves conduct/convect heat better. But brake pads are so small (compared to the rim), I just don't see how the pads can make a big difference in the rate of heat dissipation.

[false_Aest]

Originally Posted by Mark McM

How do they support the claim that these brake pads keep the rim cooler? Brakes convert kinetic energy (energy of motion) into heat. For the same amount of braking, the same amount of heat is generated. How much the heat raises the temperature will depend on the ability to dissipate the heat (i.e. conduct and convect the energy away). The brake pads won't change the ability of the rim to conduct/convect energy, so the only way that the pads can keep the rims cooler is if the pads themselves conduct/convect heat better. But brake pads are so small (compared to the rim), I just don't see how the pads can make a big difference in the rate of heat dissipation.

You and I have wondered the same thing.

The only thing that I could come up with is that they're grabbier so you can brake later and release earlier thereby allowing the rim more time to cool down before the next brake engagement.

[fogrider]

I'm not a scientist...but Reynolds requires use if their pads or it voids the warranty. And use in the SF bay area has been pretty good with the exception of one of my brakes. I got the new 'power' pads and the do work better and pretty much as advertised.

Originally Posted by Mark McM

How do they support the claim that these brake pads keep the rim cooler? Brakes convert kinetic energy (energy of motion) into heat. For the same amount of braking, the same amount of heat is generated. How much the heat raises the temperature will depend on the ability to dissipate the heat (i.e. conduct and convect the energy away). The brake pads won't change the ability of the rim to conduct/convect energy, so the only way that the pads can keep the rims cooler is if the pads themselves conduct/convect heat better. But brake pads are so small (compared to the rim), I just don't see how the pads can make a big difference in the rate of heat dissipation.

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[verticaldoug]

Originally Posted by Mark McM

How do they support the claim that these brake pads keep the rim cooler? Brakes convert kinetic energy (energy of motion) into heat. For the same amount of braking, the same amount of heat is generated. How much the heat raises the temperature will depend on the ability to dissipate the heat (i.e. conduct and convect the energy away). The brake pads won't change the ability of the rim to conduct/convect energy, so the only way that the pads can keep the rims cooler is if the pads themselves conduct/convect heat better. But brake pads are so small (compared to the rim), I just don't see how the pads can make a big difference in the rate of heat dissipation.

I think the braking track on the newer carbon rims looks slightly bigger. The newer brake pads by all the wheel companies have a larger surface area. They claim the new diagonal grooves on the pads channel air over the track and brakes to help cools while moving. I think the science of polymers and resins has really progressed in recent years. If you think the advances Boeing has made with carbon fiber in its airplanes and how suppliers like Toray had to respond, it makes sense the technology will trickle down to other uses.
All these little changes probably add up but the manufacturer claims are still probably exaggerated.

[Mark McM]

Originally Posted by verticaldoug

I think the braking track on the newer carbon rims looks slightly bigger. The newer brake pads by all the wheel companies have a larger surface area. They claim the new diagonal grooves on the pads channel air over the track and brakes to help cools while moving. I think the science of polymers and resins has really progressed in recent years. If you think the advances Boeing has made with carbon fiber in its airplanes and how suppliers like Toray had to respond, it makes sense the technology will trickle down to other uses.
All these little changes probably add up but the manufacturer claims are still probably exaggerated.

I have no doubt that changes in the materials and construction of the rim brake track can aide in the dissipation of brake heat, and therefore limit temperature - but the claim was about brake pads reducing rim temperature.

I don't buy the claim about grooves in the pads keeping the rims cool. The pads only cover a small area of the rim, while the rest of the rim surface is open to the air, and the grooves are only a small part of the pad area. A tiny bit of extra air on the rims isn't going to make a significant difference (That being said, a little extra pad ventilation can improve pad/rim contact when operating at high temperatures, but the question isn't about brake force, it's about heat dissipation). I think the idea that the pads reduce rim temperature can be chalked up as another questionable marketing claim.