# Carbon Clincher Melting - Still an Issue?



## MTBMaven (Dec 17, 2005)

I'm not a regular on the forums like I used to be so I'm not up on the day-to-day happenings. I know carbon clinchers have come a long way in the last few years. Back when I was purchasing mine about 1.5-2 years ago melting was just getting solved on high end wheels but lower end and Chinese wheels were melting like hot cakes. 

So question is, can one reasonably expect NOT to melt a carbon clincher from someone like Boyd or Williams these days? How about FarSport?

Now, I mean in the mountains. >10% grade decent for over one mile assuming braking into turns but not necessarily riding the brakes hard the whole time. Also assuming you use the right brake pads, it's not wet, etc.

Or should one sick with high-end wheels from Enve, Zipp, or carbon/aluminum from Mavic?


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## SwiftSolo (Jun 7, 2008)

The braking surface on carbon makes for poor braking, especially in the environment you described. With hydro discs brakes your braking will be more precise and carbon wheels will not be a problem.


MTBMaven said:


> I'm not a regular on the forums like I used to be so I'm not up on the day-to-day happenings. I know carbon clinchers have come a long way in the last few years. Back when I was purchasing mine about 1.5-2 years ago melting was just getting solved on high end wheels but lower end and Chinese wheels were melting like hot cakes.
> 
> So question is, can one reasonably expect NOT to melt a carbon clincher from someone like Boyd or Williams these days? How about FarSport?
> 
> ...


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## ericm979 (Jun 26, 2005)

If you use the correct pads for the rims, don't ride the brakes and don't go down super steep and extremely technical descents, carbon clinchers are fine. I have used Reynolds and a couple different sets of FarSports in the Death Ride, Everest Challenge and Alta Alpina double. All have 55 mph descents but not too much in the way of tight turns. Also in the Mt Hamilton road race, which has the steepest and most technical descent we race down in NorCal. It regularly claims multiple victims. 

But that is the steepest and most technical descent I'll use them on. We have even gnarlier ones which I only ride on aluminium rims. I'm 145 lbs and a long time motorcyclist so I am confident on descents.

Edit- most places you're hard pressed to find a true > 10% descent that lasts for a significant distance. If it's really > 10% (not just marked with a road sign, that's only the steepest section) for long, and it's got tight turns, I'd not ride it on carbon rims.

I've also ridden Onion Valley (9% for 13 miles, steepest 10 miles in California) and Horseshoe Meadows on FarSports.


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## Kerry Irons (Feb 25, 2002)

MTBMaven said:


> lower end and Chinese wheels were melting like hot cakes.


I can't imagine the circumstances in which hot cakes (pancakes) would melt. Now butter on hot cakes, yes. But hot cakes? No.


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## MTBMaven (Dec 17, 2005)

Cute Kerry, that made me smile. Thanks!

@ ericm979. Thank you, that is the kind of information that helps. I've ridden Death Ride as well as Horseshoe Meadows and Whitney Portal. Knowing you've descended these mountains on FarSport wheels is impressive. I live in the LA area so common descents are Highway 39/Azusa , GMR, seGMRveral step ones in the Santa Monica Mountains. Deer Creek comes to mind as a decent that always made me worry I'd melt a tube with aluminum rims.

Curious what FarSport wheels you have? I have some with the basalt brake surface but not their newer rims with some high temp brake area. Lastly, what pads are you using?


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## coachboyd (Jan 13, 2008)

I can only speak to the testing that we have done on our rims but will provide a little testing numbers as well. It's kind of long, but. . . 

If you ride the brakes long enough on any carbon wheelset, you can still have issues. I have seen rims damaged from even the brands that claim they've never had a wheel damaged from heat. We have a Gran Fondo here that goes down a 3 mile downhill with most places around 15-18% in grade. In the first year (2012) I think there was something like 19 sets of carbon clinchers across all brands that melted. The second year it was about 30 degrees F when we descended that mountain and I didn't hear any reports of any rims having issues. This past year it was warm and sunny, about 65-70 degrees by the time most people started descending. So far I have not heard of any issues, but I am sure there were a couple. With the event being in Greenville, we had quite a few people riding on our newer carbon clinchers and everybody was perfectly fine.

That's not to say issues can't occur. We encourage proper braking technique with all of our customers and try to educate people on how to ride and brake. We just don't hand the keys to the shiny new toy over and hope all will be ok. Things like modulating the brakes and proper brake pad selection can make a huge difference.

I am about to write a blog about proper braking technique as there is a lot of people that think modulation means they should alternate between front and rear brakes. That is probably the worst thing you can do on a steep descent as it puts almost all the braking force (and heat build up) and you front wheel. Then when you are riding the rear brake, it's not doing hardly anything to slow you down, on very steep descents if you hold just the rear brake you will actually speed up). The best method for modulating the brakes is to brake hard with both the front and the rear at the same time. Brake fairly hard for a few seconds and then release with a few seconds. This allows the rim temperature to rise and then fall.

Getting to the testing we have done on our rims. There are two main tests that we look for. The modulation test and the torture test. Conditions are the same, there is 75Kg of weight pushing down on the wheel, the wheel is being run at 25km/h and the braking force is 12KgF (pretty high in terms of braking power).

The first test is the modulation test, and we did 4 seconds on, 4 seconds off. The rim temperature would rise and then fall. After about 10 minutes of this, everything stabilized and the temperatures would reach the same peaks and valleys on every rep. The test ran for on hour and we finally stopped it because there's no point in going on any further. The max temperature reached was 68 degrees Celsius with our brake pads that were designed with the rim, and 110 degrees Celsius with a different set of pads (that are popular but build up more heat). So, with good modulation and running in an on/off braking method you can run the brakes as long as you want.

The next test was the torture test, which is basically run the brakes continuously until something bad happens. The exact same braking conditions (weight, speed, braking force) were used as before. Temperature and PSI were monitored throughout the test. The temperature gradually rose over the first minute and a half of the test and then plateaued at about 110 degrees Celsius. It stayed at this temperature until the seven and a half minute mark. At this point the heat had kept transferring into the tube and tire and the PSI in the tire had risen to 175PSI (started the test at 100). This was enough to cause the tube to blow, and then blow the tire off the rim. The rim was holding up fine, but blowing off of the tire was enough to damage the rim with the weight on it. We obviously do not want people to pop tires going down mountains, which is why the proper braking technique is encouraged.

We then did the test with the other popular pads (that we don't recommend). Same exact braking conditions as before. In that torture test the temperature rose very quickly and very high, getting to over 200 degrees Celsius in just under 2 minutes. This was enough to melt the rim and cause a failure. 

So, the heat issue has improved by leaps and bounds since even 2012 on a lot of different models. We still see rims being melted from time to time across all lines, but the newest stuff from most brands seem to have really stabilized. To me, it's a three part approach. . having rims that can withstand very high temperatures (180 degrees Celsius and above), having brakes pads developed with those rims to help keep the temperatures lower, and having people understand to pulse both brakes at the same time vs. riding and dragging the brakes the entire way down a mountain to control and limit speed.


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## tvad (Aug 31, 2003)

coachboyd said:


> We have a Gran Fondo here that goes down a 3 mile downhill with most places around 15-18% in grade.


I read your whole post Coachboyd, but this quoted sentence made the biggest impression. Three mile descent at 15-18% grade? Yikes. That's hairy. IMO.

I would ride my aluminum wheels in that situation...and I _love_ my carbon clinchers.


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## goodboyr (Apr 19, 2006)

I'm having trouble understanding how tire pressure can rise by 75 psi if the wheel temp rises 180 deg c at most. PV=nRT .............


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## ericm979 (Jun 26, 2005)

MTBmaven- I have done the Mullholland Challenge a number of times and use aluminum rims because of Deer Creek. I think it'd be ok for me to descend it if there was no traffic but about half the times I've done it there's been car traffic slowing me down. The rest of the roads in that ride would be no problem for me on carbon rims.

The traffic issue is a problem in the Levi's Grand Fondo which is the ride Boyd is referring to. There it's other bikes which are causing the slowdown, but either way if you're having to brake because of traffic you will be braking much more than you'd need for the descent. Something to keep in mind. Even in races you can get stuck behind someone or something going slow.

My FarSports have the Basalt brake surface or the new "high temp" surface. I'm using their older blue pads or older Reynolds blue pads, which seem to be the same. Their new blue pads, and new Reynolds, seem to be of a different compound which brakes ok but squeals. Their "ceramic" pads are nice and stiff and quiet but don't brake very well. SwissStop yellows should not be used, they put a lot of heat into the rims. Bontrager cork (also recommended by FarSport) brake well but squeal when you brake hard.


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## ibericb (Oct 28, 2014)

goodboyr said:


> I'm having trouble understanding how tire pressure can rise by 75 psi if the wheel temp rises 180 deg c at most. PV=nRT .............



Simplified .. [P1 V1/T1] = [P2 V2/T2], T in degrees Kelvin
Assume V1 = V2
So, P1 T2/T1 = P2
use deg K, T1 = 294 (21 C), T2 = 473 (200 C)
T2/T1= 1.6

It's probably in the ballpark given the challenges to accurately measuring pressures, and additional contributions that may come from outgassing from the tube at elevated temperatures.


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## coachboyd (Jan 13, 2008)

ericm979 said:


> The traffic issue is a problem in the Levi's Grand Fondo which is the ride Boyd is referring to.


Actually it's the Hincapie Gran Fondo. I have never done Levi's one, but from people I have talked to who have done both, the descent of White Oak Mountain (which is used in the Hincapie) is way worse than anything in Levi's.

We have some good mountains here in the Carolinas!


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## November Dave (Dec 7, 2011)

I can corroborate what Boyd's seen in his testing. We've got lab tests that show similar rates of heat build and maintenance/dispersion, and our rims have fairly similar heat tolerances from what I know. 

The nagging question to us being "okay that's great, but what temperature happens on the road?" To answer that, we went to Vermont and North Carolina (they DO have some good mountains in the Carolinas!), specifically Smuggler's Notch and Beech Mountain, and rode down them using various braking techniques and with various rider weights. 

The highest temps achieved were very similar to Boyd's highest temps - 215* f for us. This was achieved in two ways. First was riding the brakes continuously down Smuggler's Notch, which is a very very steep and switchbacked 1k section, with a rider weight of 200 pounds (me with a 40# backpack on), maintaining a speed of very close to 10mph. 

The second was going much faster, around 22, down Beech Mountain outside of Boone, NC. This was a continuous application of both brakes as well, basically no letup, maintaining that speed. I weighed 185# in this instance - me with a 25# backpack. Based on comparisons to other tests, we can assume that the extra 15# would have added some extra heat but the number of times one can climb Beech Mountain in one day, especially carrying up to 25% of his bodyweight in a backpack, is limited. This was the very epitome of "dragging the brakes." Temperature was measured by a scanning thermometer that I kept tucked in the leg of my bibs. The differences in my temps to Boyd's could easily be captured in the few seconds that it took to deploy the thermometer and get a measurement. The rims begin to cool quite quickly, which also reinforces how beneficial good technique is. 

I'd honestly prefer not to ride either road with any brake or tire in heavy rain, it would be quite dangerous. These are crazy roads, the 1% of what you might experience - that's why we went to them. 

It's certainly not impossible to have a heat-related failure, but what failure is impossible to have? A part of this discussion that always puts me on edge is the thought-by-comparison that it's impossible to have a braking-related failure of carbon or aluminum tubulars, or aluminum clinchers, or any kind of disc brakes. Braking technique is very important and limits of brake systems should always be respected.


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## goodboyr (Apr 19, 2006)

ibericb said:


> Simplified .. [P1 V1/T1] = [P2 V2/T2], T in degrees Kelvin
> Assume V1 = V2
> So, P1 T2/T1 = P2
> use deg K, T1 = 294 (21 C), T2 = 473 (200 C)
> ...


Sorry. He said the rim melted at 200 c or so. The tire blew at 110 c. So..............


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## ibericb (Oct 28, 2014)

Not really. The 200 deg C failure is correct, but he didn't note at what temperature the tire blew in the torture test. The 110 deg C temp was the steady state temp in the modulation test. That temp was passed in the torture test. I used 180 deg C because that is what you had cited n your question.

FWIW, ENVE on there lab test system noted the highest temps they have seen are 350 deg F, or 175 deg C on their wheel systems; it's not with real world riders on bikes.

What I had taken from several sources is that a 1.5-1.6 X increase in pressure with a clincher in possible in extreme situations, but probably quite rare.


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## coachboyd (Jan 13, 2008)

goodboyr said:


> Sorry. He said the rim melted at 200 c or so. The tire blew at 110 c. So..............


In the test where we ran the brakes continuously for seven and a half minutes is the test where the tube burst at 175PSI.

This is where the rim had plateaued at 110degrees Celsius. That heat the was constantly in the rim was constantly transferring into the tube. This would cause the tube to gradually rise in terms of pressure as there was constant heat going into it. When the test first started the air temperature was around 26 degrees Celsius. 

On the test where the rim failed, this rim got up to the 200 degrees fairly quickly because of the brake pads. There was not enough time for the heat to transfer through the rim into the tube and tire to cause the PSI to rise. It takes quite a while for the tube to rise in pressure because of the heat having to transfer through a carbon rim.


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## goodboyr (Apr 19, 2006)

coachboyd said:


> In the test where we ran the brakes continuously for seven and a half minutes is the test where the tube burst at 175PSI.
> 
> This is where the rim had plateaued at 110degrees Celsius. That heat the was constantly in the rim was constantly transferring into the tube. This would cause the tube to gradually rise in terms of pressure as there was constant heat going into it. When the test first started the air temperature was around 26 degrees Celsius.
> 
> On the test where the rim failed, this rim got up to the 200 degrees fairly quickly because of the brake pads. There was not enough time for the heat to transfer through the rim into the tube and tire to cause the PSI to rise. It takes quite a while for the tube to rise in pressure because of the heat having to transfer through a carbon rim.


? OK. Now I am puzzled. Unless the temperature went up to 180 c or so, the psi won't rise. Pressure drop doesn't change due to "steady heat input", it rises due to temperature changes.


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## ibericb (Oct 28, 2014)

If 110 deg C was the max temperature in noted in the source (wheel), then you won't move heat to the tube beyond that temp (simple heat flow transfer issue). 

A rise from 26 C to 110 C would lead to an expected isovolumetric increase in pressure of about 1.28X, not 1.75X. Not doubting the blowout, but the pressure question is valid.


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## ericm979 (Jun 26, 2005)

Since CF does not conduct heat well the temps will vary quite a bit across the rim. So I wonder where the temp sensor was?

Thanks for November and Boyd posting test results. If you guys write more detailed blog posts please put a link here.


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## spdntrxi (Jul 25, 2013)

I did Levi's on my enve 3.4 this year.. Never again. The had a big wreck near the metal bridge.. We all piled up waiting for them to open the roads at the station above the descent. Can you imagine the traffic! I stopped because it was simply not safe and I think I descend alright 

Next year I'm bring Al clinchers


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## aclinjury (Sep 12, 2011)

I'd like to see a test something like this (short of being real world). Put a bike with the wheels on a roller. Put a 175-lb rider (or a bag of 175-lb weight) on the bike. Now the spin the wheel up to 60 mph. Now jam on the brake as hard as possible (without locking up the wheel) until the wheel speed slows down to 10 mph. Then spin the roller up again to get wheel speed to 60 mph, jam on brakes hard again to slow down to 10 mph. Repeat, and oberve temp data. 

And the roller should have some weight on them to add inertia (because during a real world descent, gravity always act to pull the bike down (ie, speed up the bike), and this is unlike riding on a flat surface. So roller should have some weight to them to provide inertia.

I believe manufacturers are not testing their rims rigourous enough to simulate real world conditions, and that's why we still see rim failures (even from the big makes) yet they continue to show us their fabulous data (however, data acquired under condition that is not close to real world). If the condition was closer to real world, then there wouldn't be so many rim unexpected failures, because rim manufacturers would be able to tell their users exactly under what condition could they expect the failure to occur. Testing protocol, in this case, is critical to the real world application of the data.

On another note, before every long and steep descent, I always let out a quick tap of air in both my front and rear tires, aluminum or carbon. A quick tap (not a squeeze!) of the tube-valve lets approximately 10-15 psi out, depending on how much psi was in the tire before the airletting (I run 90 psi). After doing this airletting procedure, by the time I'm done with any decent descent, my tires always feel just as hard as when I started the climb. So this goes to show, if anything, letting out 1 quick tap of air is absolutely fine and I'm tempted to say even say "recommended" for carbon rims.


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## redondoaveb (Jan 16, 2011)

I've done the same steep descent on my aluminum Neuvation clinchers and Farsports 50mm carbon clinchers and when I stopped at the bottom I felt the brake track on each. The Neuvations were so hot I couldn't even touch the brake track. The Farsports were barely warm.


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## aclinjury (Sep 12, 2011)

MTBMaven said:


> I'm not a regular on the forums like I used to be so I'm not up on the day-to-day happenings. I know carbon clinchers have come a long way in the last few years. Back when I was purchasing mine about 1.5-2 years ago melting was just getting solved on high end wheels but lower end and Chinese wheels were melting like hot cakes.
> 
> So question is, can one reasonably expect NOT to melt a carbon clincher from someone like Boyd or Williams these days? How about FarSport?
> 
> ...


I ride GMR and Hwy39 a lot of the Zipp 404 Firecrest, and absolutely no problem. I'm also under 120 lbs. But a buddy of mine, 168 lbs, he's an absolute demon going down GMR (top 6 on Strava) and he has passed even motorcycles goind down GMR, he rides Enve SES 6.7, and again he has zero issue with those rims (and he doesn't even bother to let some air out before his descent). Needless to say, he is quite a skilled descender and barely needs to brake (dude rails corners faster than motorcycles).

Now if you're descending from the top of Baldy, then that 2 mile section from the top can be hairy fast, with lots of 15%-20% switchbacks, and it is the braking into these switchbacks that will put the most heat into your rims. On my Dura Ace aluminum rims, during cool weather months (such as now), the rims get warm to the touch (yes, I have actually stopped and feel the temp of the rims!), but never hot to the touch where you feel like your fingers are burning. On the Zipp 404, it feels about as hot as the Dura Ace, nothing like "melting hot" and no smelly brake pads (due to extreme temps). Again, this is under cool weather, and I'm under 120 lbs. If I was 160 lbs and riding under hotter weather, than I would take the aluminum rims going down from the top of Baldy to Baldy Village. Going down Hwy39 (from Crystal Lake, carbon rims is fine).

Now for the Santa Monica mountains, like said above, Deer Creek is one of the hairy descent, but Tuna is also hairy. Though I have not used my Zipp 404 Firecrest for any Santa Monica mt. ride, I did use my Dura Ace aluminum, and the aluminum pass Tuna and Deer Creek without a flinch, and the DA rims did not feel any hotter than going down from top of Mt Baldy. Again, I rode in the DA rims during cool weather (such as now). but I'm under 120 lbs so I'm not going to stress any rim!

*disclaimer: what we human feel as "hot" when touching aluminum (metal) and carbon, is not necessarily what the heat content is in those rim. There is a subtle difference between "temperature" and "heat". You can google this concept up. But touching a metal surface will always feel a bit "cooler" than touching a carbon surface even though both surfaces are at the same temperature. Imagine touching a metal pole and a wooden chair in the same room. The metal pole feels cooler than the wooden chair, yet both metal pole and wooden chair are at the same temperature (ie. at room temperature).

But to get back to your question regarding carbon rims and heat, the latest generation of carbon rims from the big makes are far far better than what was out there a few years ago, even a couple years ago. Zipp claims that their latest generation Firestrike rims has ceramic particles embbed into the resin, and claims that braking is just as good as the best aluminum rims in both wet *and* dry conditions. And I'm guessing by the next generation of carbon rims (in 3 years?), folks will not be even asking this questiong regarding braking on carbon rims. The improvement is really in the resin.


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## MTBMaven (Dec 17, 2005)

All, thank you so much for all the great feedback. Boyd, especially great work!


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## Mr645 (Jun 14, 2013)

Why not consider something like the Shimano Dura Ace C24 or C35 wheel?


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