Barrettscv 

I have tubeless ready carbon fiber rims on my rim-brake road bike. I've had two blow-outs while using tubes. Both happened after braking for a stop sign after descending a half mile hill of about 15% or more.

The rims are heating up and causing the tubes to fail.

Do tubeless tires and sealant eliminate this risk?

On long descents that are moderately steep. I alternate front and rear braking and can avoid a blowout. But on shorter steep hills stopping quickly is required.

terrymorse 

No, switching to tubeless will not prevent a heat-related blow off.

Heat does not cause tubes to fail. Heat causes tire blow offs.

Heat:

• increases the temperature of the pressurized air
• increases the internal pressure of the tire

If the internal pressure exceeds the rated pressure for the tire (and rim), the tire's bead will blow off the hook of the rim.

What can you do?

1. lower your tire pressure (good bet that you're already running too high a pressure, see this Silca tire pressure calculator)
2. install wider tires, if your frame will accommodate them
3. learn how to brake better (coast, coast, coast, brake, coast, coast coast)
4. get a bike with disc brakes

Barrettscv 

Good explanation, thank you.

My disc-brake endurance bike just got the prime spot in the bike quiver and the rim brake road bike will only come out on perfectly flat routes. The Endurance bike was already the most versatile bike in the quiver, It's now the bike for any routes that aren't perfectly flat.

phrantic09

…..

eduskator

Did you try thicker tubes?

It may be worth trying tubeless, especially if it's the tube that blows and not the tire.

terrymorse 

Tubes don't blow up or melt. The tire fails to hold the pressure, the tube escapes, boom!

Trakhak

Exactly. The tire already contains the total pressure of air in the tube (and is all that is keeping the tube from exploding). A "melted" tube would not alter the pressure inside the tire.

phrantic09

Regardless the bead rim interface on a TL or TLR tire is much stronger than a normal clincher, making it less likely- especially if running proper pressures

t2p

yikes - what brand/type rim and tire ?

DaveSSS 

I climb and descend quite a bit in Colorado and I've hit 57 mph, but I have no road conditions that require much braking. If the descent is winding, I brake briefly before each corner, if the turn radius requires it. The only road condition that might require extensive braking, is a rough or pot holed surface. I'd stay off that kind of road.

Racing Dan

Are you absolutely certain its the tube failing from heat? What kind of tube is it? - Might be the tyre blowing off of the rim, causing the tube to blow out, or the tyre bead separating from heat.

Tubeless carbon rim .. the hookless kind of TL rim?!

terrymorse 

I doubt that. Do you have any references to support this claim that tubeless tire beads are stronger?

I’ve inspected the beads on tubed and tubeless versions of the same model tire. I saw nothing in the bead structure that would suggest a difference in blow off resistance.

Trakhak

Yes. People were reporting clincher tire/hooked rim combinations where the tire was almost impossible to install on or remove from the rim decades ago, long before tubeless tires and rims showed up on the market. I remember sometime in the 1980s listening to a sales rep for a tire manufacturer who claimed that if his tire was giving us problems, we were just using the wrong technique. So I handed him the tire and wheel in question and asked him to show us the correct technique. After struggling with the tire and wheel for 15 minutes, he gave up.

chaadster

Innertube manufacturers disagree with your assessment, and many warn about overheating the tube. There’s less fuss about it these days what with disc brakes n’ all, but Tubolito still indicate their S model is for disc only because of the heat issue.

Here’s a quote from Vittoria on the matter, from the VeloNews Technical FAQs column. It’s particular to latex, but also address the issues of butyl and heat generally:

“What is the heat tolerance of the average lightweight butyl tube and latex tube?
If the tube reaches the level of 100-140 degrees Celsius, all kinds of inner tubes will be destroyed.

And, how often do carbon clinchers reach temperatures that would lead a latex tube to fail?
This really depend on several factors, such as rim construction, -size, -resin and -tape. But mainly [it depends] on the end-user brake skills.

Agree that, “shorter, more powerful braking produces less heat buildup than does prolonged braking.” Similar to car brakes.

It’s not the tire bead, but the tube that cannot withstand the heat and give a sudden high pressure to tire bead. By the way, our tires run through a CQ that request 200 percent of the suggested maximum pressure. Example: Open CORSA CX 23mm 10.0 bar max tires have to withstand 20.0 bar at our derailing machine.

Is there another reason besides the heat issue that makes latex tubes unsafe for carbon clinchers?
Tubes are a rather sensitive product in general. Either Latex- or superlight Butyl tubes tend to explode suddenly, if not being used correctly. Some rules need to be followed:

1. Do not overheat the system
2. Do not lock the tube in between tire bead and rim hook
3. Prevent tube over-stretching in general — use recommended air pressure, rim tape and tube size
4. Prevent any sharp edges in the system
5. Prevent contamination with any oily substances”

— Christian Lademann
Product Manager, Vittoria S.p.A.

https://www.velonews.com/gear/techni...ubes-and-more/

terrymorse 

Granted, tubes can soften at very high temperatures, leading to failures. Certain thermoplastic TPU tubes have low melting points, leading manufactures to "cover their backsides" warnings like "never use these tubes with rim brakes (triple-bang!)".

But a melted tube does not cause a sudden blow off (the subject of this thread). Blow offs are caused by the tire bead coming off the rim hook.

If your tire goes "boom", it is not because your tube failed.

chaadster

The OP clearly states “blow-outs,” not “blow-offs.”

terrymorse 

Semantics. Two phrases that describe the same phenomenon, with the second one being more accurate.

If you hear a "boom", the tire came off the rim.

Kontact

Reading the OP, I can't tell if he's having blow offs. If the tube suddenly failed internally due just to melting, I don't see why you wouldn't get a popping noise as the pressure escaped out through the rim. Many would call that a "blow out".

The OP ought to relate whether the bead came off or not, and what the tube looked like.

Kontact

Also, is this a front tire phenomenon? If not, you're building up heat using the ineffective rear brake too much.

chaadster

Could be, could be not. It is you who introduced the ideas of the tire coming off the rim and "boom" sounds, not the OP, and it seems a common distinction to me that a "blow out" is sudden, rapid, total air loss and a "blow off" is indeed the tire coming off the rim. In any case, it's easy for the OP to clarify that.

terrymorse 

People can hypothesize day and night about melting (actually softening) tubes, how they might fail, and what they may sound like when they fail, but here's something that is unequivocal:

The common heat-induced failure mechanism is tire blow-off, caused by overpressure [EDIT: and the softening of the tire's bead]. It has been happening the same way, ever since cyclists with clincher tires started descending steep roads. Without exceeding the temperature limit of a butyl tube, an overpressure of 50% is possible, which is more than enough to blow a tire. Braking steadily for 30 seconds on a steep downhill will do the trick.

chaadster

Not hypothetical; something happened to the OP, so only need clarification, although it seems likely that if the tire de-beaded, they'd have mentioned it, but yeah, they only need to clarify.

Maelochs

Agree. Absent more information from the OP none of us know what we are talking about .... How's that for a straight line?

Polaris OBark

(1) No, as others have said. It will potentially make the problem worse.

(2) This is exactly why I insisted on getting hydraulic disc brakes. Those grades are prevalent where I live, and I am a bit paranoid on descents, and ride the brakes more than I rationally need to. If there was ever a compelling reason to get a new bike, it is this.

Polaris OBark

Which, although I am sure you aren't intending it, is potentially the best reason I have yet heard for using the rear brake more. If it is a front tire phenomenon, there is a good chance he is posting from the graveyard.