How hot do your carbon clinchers get?

[RocketRacing]

This is a tough question, so i will say we are measuring by feel. Lets define options as: Cool, warm, hot, very hot (so hot you can’t keep your finger on it.).

Also, the longer we ride before feeling... the cooler the rim will get.

The true question here, is “how hot must a rim get before it will blow. More specifically a latex tube. And i know that depends on braking texhnique, rim brake track design, air temp, rim temp, pad compound, rider speed, rider weight, etc.

I guess what i am trying to sort is if layex tubes pop at shockengly low temps, or if you need to be running the rims so hot that they hurt to touch them.

My rims have never progressed passed “warm” on our local descents. And i run latex tubes, and have yet (in my short time in the hobby) had a blown latex tube (due to heat).

[TonyM]

I suppose that the rims have to be very hot and for quite a while until the latex tube blows.
That's why it is more a problem for heavy guys and/or poor downhill riders.

I am not that heavy and quite good at downhill on the road but I always used butyl tubes and aluminum rims whenever I did some alpine climbs. Better safe than sorry. The risk to have a problem with the latex tube and the carbon rims is maybe small but the consequences can be quite terrible (just think about the crash of Froome today at the Dauphiné...). For everything less than alpine climbs I always used latex tubes and never had a problem however.

[TobinHatesYou]

I've seen people burn their calves after longish >10% descents while standing over their bike.

[Calnago]

I guess what i am trying to sort is if layex tubes pop at shockengly low temps, or if you need to be running the rims so hot that they hurt to touch them.

I think with latex tubes and clinchers it’s more about the ability of latex to find its way into every nook and cranny, and the higher the pressure (high temps) the more it will be able to creep. I don’t think they just spontaneously blow up unless they can find an escape route which typically is underneath the bead of the tire or a spoke hole and it can blow the bead off the rim along with it when it blows. With tubulars, the tube is fully contained and cannot escape the tire unless the tire itself gets cut right through.
I’ve stopped only a few times due to what I thought could be excessive heat happening. One time was in Arizona coming off a steep descent with lots of turns and an ambient temperature of over 100F. Alloy rims and butyl tubes, but the principle was the same. I did feel the rims when we stopped part way down and you could have fried an egg on them. On another occasion while having lunch at the restaurant about 6km from the top of Mont Ventoux, I remember two “bangs” as riders would come down then stop there for a bit. If you know you’re going to be descending a long technical descent where you’ll be using your brakes a lot, it’s probably not a bad idea to let a bit of pressure out of your tires beforehand to give yourself a little leeway. And or stop to take a picture or two. I mean, unless it’s a race, why not.

[pdlpsher1]

It's not hard to find out. Just take a balloon and put a lighter under it. Vary the heat and see what happens to the balloon

[Marin]

Even been in a Sauna? You can sit on wood that has 100°C.

You'll burn your fingers on metal at 60°.

Touching warm carbon doesn't tell you what you want to know.

[RocketRacing]

Even been in a Sauna? You can sit on wood that has 100°C.

You'll burn your fingers on metal at 60°.

Touching warm carbon doesn't tell you what you want to know.

Thus my origiNal question, and this thread. How hot were your carbon rims when the latex tube failed due to heat? Or, if that has never happened, how hot have they felt, and they had no issue.

Most failures i have read about (or experienced) were not failures due to the tube, but the rim tape/plugs/equivalent becoming soft, and then puncturing, resulting in a spoke hole popping the tube.

Is warm a sign of near death? Is warm no worse then they will get sitting in the sun? Or do a lot of us really have no idea? (Realizing that touching a rim is not a hard science and accuracy will be suspect... but i am looking for generalizations... again, if a carbon rim needs to be able to cook and egg/burn a leg on contact, to cook a latex tube... that is a useful to know, as my rims have never progressed beyond mildly warm).

[alcatraz]

After coming down some steep descents (maybe 200 altitude meters in 1-2 minutes) and braking without care for the rims, after stopping and feeling the front wheel brake track I could almost burn myself. I'd guess I was at around 70 degrees C maybe.

That means I might have been peaking at (wild guess) 120 degrees perhaps? (I have a 70kg total riding weight)

I think latex is in the risk zone around 150-200C. I wish I knew the exact number for the mixture of latex used in tubes.

[RocketRacing]

After coming down some steep descents (maybe 200 altitude meters in 1-2 minutes) and braking without care for the rims, after stopping and feeling the front wheel brake track I could almost burn myself. I'd guess I was at around 70 degrees C maybe.

That means I might have been peaking at (wild guess) 120 degrees perhaps? (I have a 70kg total riding weight)

I think latex is in the risk zone around 150-200C. I wish I knew the exact number for the mixture of latex used in tubes.

Thanks. That says a lot.

I will ask josh at silca through the marginal gains podcast. I am sure he has interesting stories/data

My warning to others reading this is that is may be less about the latex itself, and more about rim tape gettin soft and this stretchy as the rim heats up. Combine this with heat increasing air pressure, and together the system works to bust through the rim holes.

[robertbb]

Seems to me alloy/metal parts seem to take on the outside temperature moreso than any carbon part.

Brake levers, bars, stems.. and yes.. wheels, seem to be very cold to touch in freezing weather and likewise very hot to touch when in the sun and in hot climates. Carbon parts seem to be more consistent in their temperature.

How this translates to carbon clinchers and tubes popping, I have no idea. I get there is friction involved. But i've never, ever, ever had an issue with Carbon Bora's running Michelin A1 butyl tubes (which are every bit as light as Latex tubes and actually hold air). Long alpine descents.... never an issue.

[TobinHatesYou]

Aluminum is a fairly good conductor...it was the material of choice for heatsinks and even transistors before copper replaced it in tech. Pure carbon is no slouch at conducting heat either, but the “carbon” in bikes is a composite of carbon tows/fabric and plastic/resin. So the resin is a pretty big variable when it comes to thermal conductivity and glass temps...also the composite nature of CFRP means you’ll get tiny air gaps/bubbles in the structure. Obviously air is a poor thermal conductor / good insulator.

Basically alloy might get hot faster, but it will also cool faster when given a chance. CFRP will insulate the heat on the pads, and perhaps heat up the calipers/brake cable/etc., while steadily building up heat in the rim too. That heat won’t spread to the rest of the rim either thanks to the insulative properties of the composite...whereas a deeper 30mm alloy rim will cool faster than a shallower box section alloy rim. The heat built up in the carbon /resin brake track will take longer to dissipate, which is why carbon rims end up way hotter given the right conditions.

[Marin]

Brake levers, bars, stems.. and yes.. wheels, seem to be very cold to touch in freezing weather and likewise very hot to touch when in the sun and in hot climates. Carbon parts seem to be more consistent in their temperature.

No, the carbon, metal, leather and plastic parts on you bike will all have the same temperature.

They just conduct differently and this is what you feel - how fast heat is moved away from or into your fingertips.