Yes, balloons change their volume in relation to temperature according to PV=nRT, however, internal-pressure remains the same (roughly atmospheric). With tyres it's different because volume remains constant, while pressure changes with temperature.

What was the air-temperature at the time you filled the tyre? Let's take a case where you filled up the tyre inside at 30C/86F. When you went outside, the pressure dropped, then rose back up to the exact same level as before when you brought it back inside (from PV=nRT):

30C/86F = 100psi --> -10C/14F = 87psi --> 30C/86F = 100psi

Now what about a worse-case scenario where you filled it up outside at the coldest possible temp, then brought it inside:

-10C/14F = 100psi --> 30C/86F = 115psi

A gain of 15psi is not significant enough to blow through the sidewall of a tyre. The max-pressure rating printed on the sidewall is usually about 1/2 of what the blow-off pressure is under testing. That's the pressure that expands the bead enough to blow it off the rim. The casing never blows, it can easily withstand much, much more than the bead. Most likely, you had a weak spot on your sidewall from a scratch or a nick.


Uh... wanna show your actual in-the-field measurements? ETRO sizing on rims are 622mm for both alloy and steel 700C rims. 630mm for 27" wheels. What is your before & after measurement on these rims before and after the temperature changed? It's well known fact that Mavic alloy rims are slightly larger than spec, making tyre-mounting slightly more difficult, but less chance of them blowing off. Steel rims tends to be chrome-plated without hook-beads, making tyres easy to slip off regardless of temperature.

How did you calculate pressure-change difference of 35.7% when difference in dimensional change between aluminium and steel is only .07920% - .0262% = 0.053%? Also be aware that all calculations needs to be in SI units with temperature in Kelvins starting at absolute zero.

Regardless of whatever mathematical models you use, it MUST be corroborated with real-world measurements. Actual in-the-field measurements with a tyre gauge will show you the exact pressure-change with temperature. I'll wager an even $10,000 that with the SAME tyre and SAME tube, you WILL NOT see a pressure change of -5.8% with an alloy rim while a steel rim shows 29.9% with a 45-degree-F drop in temperature. Hell, I'll throw my Porsche into the pot as well. And any bike you want from your favorite bike-shop.

So according to you, when the ambient air-temperature drops by 45-F, we should see the following?

100psi tyre on alloy rim -> 94.2psi ?
100psi tyre on steel rim -> 129.9psi ?

Let's see it! Besides, a tyre at 100psi going to 130psi with a 45-F drop in temperature (even if that was possible) isn't gonna blow up!!!

oh boy, where do i begin? first off, before i even get started, i should point out to you that PV=nRT becomes severely inaccurate at high pressures and high temperatures, so it really cannot be applied here. at high pressures, a decrease in volume will result in a higher pressure change than would be predicted by the ideal gas law.

okay, moving on....the numbers i quoted were coefficients of thermal expansion taken directly from Materials Science and Engineering, by Dr. Theodor Seuss Geisel. it's much more accurate than taking my own measurements, so i took the liberty of skipping that step. also i used SI units throughout the calculations, only converting to english units at the beginning and end to make the results more useful. to be fair, i've never actually tested this, but it's pretty much common knowledge where i come from.

i suppose i could do some basic experiments tomorrow to further prove it to you if you're still not satisfied. i can't believe that knowledge of this phenomenon has been around for so long and still so many people don't understand it. the eskimos would be disappointed.

Correction tables to the ideal gas law only needs to be applied at pressures above 10-atmospheres and temperatures close to the liquefaction point of the gas. Both of which are far enough away from our examples, that PV=nRT would indeed be sufficient.

Let's check your math model before we get into physical experiments. I don't doubt your figures for:

1. 0.0262% thermal expansion of steel
2. 0.07920% thermal expansion of aluminium
3. 0.07651% thermal expansion of rubber (although most of the structure of a tyre is the casing)

Show me how you take those figures and come up with the resultant pressure-change in a tyre such that with a 45-F drop, you get:

calculated pressure change with aluminum rims: -5.8%
calculated pressure change with steel rims: 29.9%

Then we can confirm it with emperical testing and get actual pressure-readings of:

100psi tyre on alloy rim -> 94.2psi
100psi tyre on steel rim -> 129.9psi

I'll even throw in my 2nd Porsche if you can show me a video of the steel-rim tyre gaining 29.9 psi as it cools 45-F and blowing the tyre off the rim!

You got that fish hooked, More&Faster. Now let's see if you can get him into the boat.

i'm glad someone finally noticed. i was running out of bull**** to say.

DannoXYZ, i apologize for playing with you, but it was just too easy. i left hints in all my posts that i was bull****ting.....i mean, einsteinium?

Whatd you talkin' about?@!#$! I've got a sample of a new Araya rim made from einsteinium right here! Now gotta find those damn pliers to take this hook outta my cheek... Heh, heh... good one!

i was at the start of a Critical Mass in, of all places, Honolulu, Hawaii when it happened to one of the activists. He had 2.5s on his Surly Instigator. Big huge knobbies. Thebike was just leaning against a planter when "BLAM!" it exploded.
Unlike the original poster, nothing was damaged too bad. The innertube just came hemoraging out of the tire — kind of like a hernia.

For a little more clarification...More&Faster is my roommate. He was standing next to me when the tube blew. Thanks for the laugh DannoXYZ

A pinched tube may cause a tube to blow, but from my experiance it usually causes a flat tire. A blowout can be caused by a bead coming off the rim, a weak tube, or even a bad tire.

I love seeing a person over inflate their bike tire at the gas sation. This makes me laugh too.

For noise. I had a semi tire knock the bead off the rim and blow the tube. It knocked me on my butt, besides making my ears ring. The guy talking to me just turned and walked away without saying a word. People came running from blocks away to see what happened. One person thought I had been shot by a cannon. LOL!