It doesn't seem far fetched to me. I have a Mavic CXP 21 (clincher) rim that will blow a tire off if the PSI is => 120, which is about what a 16g CO2 will provide. It does it every time, it's not a pinched tube issue.

The safe limit for that whee/tire combo, for me, is 100.

Or it might be a good approximation.

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It doesn't really matter what Phil is saying, the music of his voice is the appropriate soundtrack for a bicycle race. HTupolev

Yes. And actually many did not.

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________
It doesn't really matter what Phil is saying, the music of his voice is the appropriate soundtrack for a bicycle race. HTupolev

10 years.

And science education hasn't improved at all. ;)

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________
It doesn't really matter what Phil is saying, the music of his voice is the appropriate soundtrack for a bicycle race. HTupolev

If that were true, you would be blowing a tire every time you hit a bump. Pressure spike way over 120psi in the real world.

If you're tires are blowing out whenever you go to 120, either you are installing them wrong or you have some bizarre combination of rim and tire that isn't eating correctly. Back in the day there was a more-is-better mentality on tire pressure. It wasn't uncommon to see guys to be pushing 130 or 150.

It was a myth 10 years ago and it looks like it's still a myth today.

It is entirely possible that tubes that blow are tubes that have minor manufacturing defects that create weak spots in the tube, but if that is the explanation, the manufacturing defects are probably a little more common than we think.

*sigh*

Tubes can't "blow" unless their container (tire and rim/strip) is compromised. The tube is under very little stress when properly installed and inflated. If a weak point happened to give way, then it would leak air but not explode.

A tire coming off the rim is the typical cause of the explosion, probably from poor installation. Add heat and cornering forces, and BOOM!

Let me say, I've seen and heard it happen. Can't remember the year but it was at St Anthony's the day before the race, over the course of the 30 minutes I was there I heard two tires pop. The bike help folks at checkin were saying it had been happening "all afternoon."

So I am trying to reconcile my own observations with the calculations. For the ideal gas law, it makes no sense, the increase in pressure would be small. And me chemical thermodynamics is admittedly rusty.

But as you stated, if you condense the water vapor then things can get crazy.

So, looking at the dewpoint under pressure calculator here, http://www.howelllabs.com/...nversion-calculator/.

You come to the race site, temps are 80 and the dewpoint is 65. You compress that ambient air to 114.7 psia, according to the calculator, the dewpoint of the air inside the tire is now 112.4 - meaning some of it condensed - if I am thinking right.

But by the same token 112.4 is a temp you can conceivably reach on a sunny afternoon with black tires, conceivably anyway, and then that condensed water will go through a phase change and really increase the pressure in the tire once you cross 112 degrees.

And obviously with small changes in the dewpoint when you fill the tire and pressure, the temperature at which you exceed dewpoint in the filled tire can get lower than 112.

You're assuming a momentary sub-second spike in pressure is sufficient to replicate the problem. I don't think that's true.


I always assume that was the case here.

I would have thought you would have at least caught the fact that degrees is not used when dealing with Kelvin - it's simply "10 Kelvin" ;)

But by the same token 112.4 is a temp you can conceivably reach on a sunny afternoon with black tires, conceivably anyway, and then that condensed water will go through a phase change and really increase the pressure in the tire once you cross 112 degrees.

Something tells me that isn't how it works...

The boiling point increases with higher pressure, so you aren't going to be boiling water. I think the table on this page will tell you what you want to know: https://en.wikipedia.org/...ur_pressure_of_water

So the partial pressure of water vapor might increase 2psi or so if you raised the temperature from 70F to 140F.

Tyres blowing was not unusual for track singles on bike hanging on racks at outdoor summer track cycling carnivals in Australia. Much less common for it to happen at indoor tracks races. Heat maybe partly a factor at lifting the pressure a few percent, but also quite possible that something already in the tyre, a shard of glass or a metal filing, just needed the heat to make the rubber just weak enough for it to blow. Many riders would pump such tyres up a lot harder at track races than you would for road racing.

Do not leave your carbon pride and joys inside a parked car in the sun on hot day. Temps inside cars can quickly exceed 70C (160F).

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http://www.cyclecoach.com
http://www.aerocoach.com.au

I love it when a 10 year old conversation picks back up like it never stopped.

I'm going to venture a guess that tires rapidly deflate in transition due to a combination of one or both of the following:

"I neeeeeeeed new tires installed the night before my race, in my hotel room, in the dark, using an ink pen as a tire lever,"

or

When you get 1500 bikes together in one place, your chances of hearing this happen are 1500 times more likely than they are sitting in your house with your own bike.

I have a couple of thoughts.
We used to be told to pump those things as high as the sidewall said was possible. And, inside of that black tire, just like inside of a black car, it is likely much hotter than the surrounding air. (Yes, I know that white cars get hotter, too, but not as hot as black. ) Could this be enough to blow the tire off of the rim? Perhaps it takes a poor mounting job, with a bit of pinched tube between the bead and the rim? Did tubies blow this way?

I think many of us are using a lot lower pressures over the last 8-10 years since data showed that, on roads, hard tires have a higher Crr, since they have to bounce over every imperfection. (This is unlike the track where the tire is rolling over a smooth surface.) Has this reduced the incidence of blowing tires? Anyone know?

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Dick

Take everything I say with a grain of salt. I know nothing.

I always inflate my tires ( 25mm Conti GP4000 or 24mm Turbo Cotton ) like this:

Roadbike: Front 90PSI, rear 92 PSI
Tri-Bike: Front & Read 90 PSI
For races Vittoria Latex tubes
For training: Continental butyl ones

For winter-training:
28mm Conti 4-Season tires always on 80PSI.

The good things are:
* I rarely run a flat (last week was the first >12months and it was a small sidewall puncture in a turn). #not-jinkx-myself
* Very comfy and no loss on CRR compared to 100PSI (I'd even bet that 90PSI would give a better CRR then 100PSI)
* No worries at all on blowing a tire in the heat. I'm off the believe that if it happens, it's either a faulty tire/tube or bad installation.

In hot races, they recommend you depressurize your tires, and you see people loosening the pressure all the way to a almost flat tire. I'm convinced this actually increases your risk of a tire blowout compared to no deflating and taking your chance with the heat.

S.

volunteered at bike check in for the NYC Triathlon last year, in july. it was very hot the day before the race, and I heard a few bike tires explode.

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I never pump mine up over 120 and have had a few explode in the afternoon heat here in Texas. Not a myth, definitely a thing.

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About 25 years ago I had a season where my front tire blew out on the drive home from the race, after every single race. After the race, I would put my bike on the roof rack, and throw the front wheel in the hatch (Honda CRX), hang out for the awards, get lunch, etc. A few hours later, halfway home, the tire would blow. It wasn't until the end of the season that I figured out what was happening. I was using lightweight urethane rim strips instead of Velox, and sitting in the back of the car for a few hours under the glass hatch was enough to soften the urethane enough that the tube would stretch and push the rim strip through the spoke holes until the tube was thin enough to burst. With the pressure relieved, the rim strip would go back to its original position and shape. It wasn't until the rim strip finally burst along with the tube that I realized what was happening. And when people came into my shop complaining of a similar issue, 100% of the time they also had urethane rim strips...

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"I'm thinking of a number between 1 and 10, and I don't know why!"

Guys, it's not degrees Kelvin. It's just Kelvin. No degrees.....

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Swimming Workout of the Day:

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2020 National Masters Champion - M50-54 - 50m Butterfly

Noted.

But that nitpick is based on something that's still relatively new: :-)

Ref: https://en.wikipedia.org/wiki/Kelvin
In 1967/1968 Resolution 3 of the 13th CGPM renamed the unit increment of thermodynamic temperature "kelvin", symbol K, replacing "degree Kelvin", symbol °K.[4] Furthermore, feeling it useful to more explicitly define the magnitude of the unit increment, the 13th CGPM also held in Resolution 4 that "The kelvin, unit of thermodynamic temperature, is equal to the fraction 1⁄273.16 of the thermodynamic temperature of the triple point of water."[1]


Edit: corrected "nitpick" and added smiley to set tone.

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AndyF
bike geek

By "relatively new" you mean it's been around for nearly 50 years, long enough that no one under the age of 60 should have been taught *K, right? Geologically speaking, that's relatively new....

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Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

Well, it's not just the student that has to be under 60. The textbooks and teachers at the time had to be also. Do you think that when I was learning graduate thermodynamics in 1988 from a 15 year old book, that this book was current with latest resolutions of the CGPM?

And what can I say... some of us are old, geologically speaking. :-)

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AndyF
bike geek

Now that we have all of the thermodynamics out of our systems here is my experience:-)

Tires exploding in the pits is not a myth, it happens all the time and having worked dozens of IM and other tri events I think that I've never worked an event where it didn't happen. Also not a myth is the pressure rise of gas with increasing temperature, but I've never been convinced nor seen any situation where the rising pressure was a sole cause for the failure. In fact, we had an oven at Zipp which was large enough to hold two Indy Car chassis and I put dozens and dozens of test wheel/tube/tire combinations in there during the very early days of our carbon clincher development (before we had the Chariot of Fire brake test machine..) and not once was I able to blow a rim, tire or tube by simply takin it from ambient to 275F, even with latex tubes which technically can only handle ~250F, we never once failed a rim, tube or tire simply by heating it the oven to 275. We later were able to fail tires

In my IM pit and service days, I have to say that every exploding tire I've encountered was caused by one of these things:

1. Tires that should have been replaced months ago, I cannot tell you how many completely destroyed tires with casing showing through the tread, sidewall bulges, cut casing cords etc I've seen. We even found a bike at check-in once where you could see the dollar bill boot through the casing, and the owner was quite upset that we wouldn't pass the bike..he seemed to think that we were trying to force him to spend even more money on his IM.
2. Pinched tubes. I think that this is usually the result of the night before tire swap, difficult latex tube installation (also usually done the night before) or new tires/new tubes with a pinch where the tight new tire can hold the pinched tube in place for a days or even weeks of use, but eventually as it stretches out (heat helps with this) the pinch is released
3. Rim Tape problems. Always surprised to see how many people have used filament strapping tape, duct tape or other non-rim tape in their wheels (seriously..I've seen lots of these) but moreso, non-adhesive rim tapes that are pushed off center during tire/tube install which result in blowouts. Often times, the setup is comprised of all the right parts, but the rim tape shifts in a spot so that the tape edge is nearly aligned with a hole edge and likely as the thing heats up, the aluminum rim grows, pulling additional stress in the plastic rim strip and boom..
4. Old, ozone exposed or crappy tubes. I have seen at least 2 transition explosions caused by valve stem separation from the tube. This is usually the result of breakdown of the interface between the 2 materials as a result of aging, repeated inflation stresses and possibly ozone exposure which degrades butyl over time. Both of the tubes i've seen like this were very old and were also low end tubes to begin with, low end tubes contain lots of low cost fillers that make them both less elastic and more subject to aging, heat, ozone and other forms of degradation. The lesson here is that you should buy good tubes (continental, vittoria or michelin) and replace them when you replace your tires even if you haven't flatted them.

The least common cause here is going to be rim and tire size, but it really can also be a factor. We had a collection of over 200 test rims and wheels at Zipp and it was pretty amazing to see the range of sizes across them. The ETRTO specification for bead seat diameter is actually fairly loose, so when you combine that with the tire spec and then consider tire stretch you can find certain systems that are just problematic. I know we had a couple of wind tunnel wheels at Zipp that we just couldn't test as we couldn't get our control tire to stay on them at the 100.0psi control pressure despite that same tire working just fine on hundreds of other wheels.

Essentially this: High Quality tires, tubes, and rim strips that are relatively new, installed correctly and inflated to rational pressures (<120psi) have essentially a zero % chance of blowing in transition due to heat or sunlight.

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/thread.

Thx Josh!

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float , hammer , and jog

Thanks, Josh! Great to have your input! Can you say more about the bit below? I'm guessing the tire bead diameter was too large for the rim? Not an issue with tires being too narrow or wide?

The least common cause here is going to be rim and tire size, but it really can also be a factor. We had a collection of over 200 test rims and wheels at Zipp and it was pretty amazing to see the range of sizes across them. The ETRTO specification for bead seat diameter is actually fairly loose, so when you combine that with the tire spec and then consider tire stretch you can find certain systems that are just problematic. I know we had a couple of wind tunnel wheels at Zipp that we just couldn't test as we couldn't get our control tire to stay on them at the 100.0psi control pressure despite that same tire working just fine on hundreds of other wheels.