Hondo6

FWIW: the link in question does seem to work - just not with a secure HTTPS connection. What follows should be the nonsecure (unencrypted) version of the link. However, this site (bikeforums) often seems to convert nonsecure links in comments to the secure version. If the displayed link below begins with "https", cut and paste the link into your browser's URL input area, then delete the "s" from "https" to get the nonsecure version of the link. (Depending on your specific browser and setup, you may or may not get a security warning and/or have to configure your browser to allow nonsecure HTTP connections.)

https://www.smitherequip.com/lit/SE1iPDF1.pdf

I have no "dog in this fight". However, I've noticed previously that some browsers don't handle older versions of HTTPS and/or TLS very well. Unfortunately, and some websites still user older versions of HTTPS and/or TLS, or use nonsecure (HTTP) links. This can sometimes cause people to believe links are invalid/don't work when they are in fact still working links.

In particular, the Firefox browser does not handle older HTTPS and/or TLS very elegantly. I use Firefox and run into this situation on occasion. I suspect that other browsers may handle older versions of HTTPS and/or TLS similarly.

WizardOfBoz

I come at it differently. Observing that a pressure rise was measured, and that there is no added air during the ride, we are forced to conclude by mass conservation that something is driving pressure up. The idealization (the Ideal Gas law) should apply, within a few percent, for air at the 4-9 bar pressure range. Above about 2 bar, engineers generally apply a compressibility factor, z, so that the law is PV = z nRT. For air in this range, z is nearly 1 and can be ignored. Specifically for air at 300K (23C) and 10 bar z = 0.9974. So, effectively, PV = nRT. Assuming that the tire does not expand much we are left with P = (nR/V) T. The (nR/V) term can be assumed constant as a starting point. Pressure is then related to the absolute temperature proportionally. So if the inital pressure is 100psi, and we end up with 105psi, we might expect the absolute temperature to rise about 5%. Is this reasonable? Assuming we start at 20°C, or 293°K, we'd get to 307.7°K, or 35°C, or 94.4°F. That seems an entirely reasonable temperature for a tire after a ride on hot pavement. In fact, I suspect that this calcuated temperature rise is low, and that the tire does stretch a bit as pressure rises.

duffer1960

As pointed out in Post #45, should use absolute pressure in the formula. So, at sea level, start with 114.7 psi. If the end of ride pressure (absolute) is 5 psi greater, that would be 119.7 psi. The calculation becomes 293 * 119.7/114.7 = 305.8 -> 90.9 °F. Reasonable, even more so.

PS -- about 'moles', something that surprised me when I learned it, but maybe shouldn't have, is using different values for Avogadro's Number allows work in different mass units. The number 6.02 x 10^23 is the one learned in intro courses, but engineers might use 6.02 x 10^26 when working in kilograms, 'kg-mols'. Or a different number if working in some other odd units like pounds.

smd4

Those are some pretty high pressures!

pdlamb

Remember to subtract the 14.7 psi for sea level pressure to convert absolute pressure back to gauge pressure.

It's higher than I like, which is why I use wider tires so I don't need to pump them up to 100 psi. If I were riding 23-25 tires, I'd probably need the 100 psi to prevent snakebite flats.

smd4

I was kidding...I think duffer1960's numbers are off about 100 pounds...

GhostRider62

I started today's ride with tires at 68F. Ambient temperatures during the 90 minute ride ranges from 77-80F. My tires were 117-120F at the end of the ride. Tar was melting on the chip seal for us non-analytical types.

2manybikes

What pressure did you start at?

cyccommute 

You do understand equivalencies, don’t you? If one thing is equal to another, it can be substituted for that thing. If you have a certain number of particles, you can use the number of particles in the equation. Of course, you have to change the units on the gas constant to get the right answer but that is trivial.

The discussion, by the way, isn’t about the Ideal Gas Law but Avogadro’s Law which states

Here’s the original paper in English if you like.

My statement is not incorrect.

No joke. I clicked on the link and it went right to the page. Here’s the link
https://www.smitherequip.com/lit/SE1iPDF1.pdf

From the text of the PDF

Yes, I made up that statistic but it isn’t that far off. Most people don’t understand moles and many…I’d say most…have never been exposed to the idea. Of those who have been exposed to the idea, most don’t remember it.

It is most certainly not incorrect. Yes, a mole is a number of items but just like a score or a dozen or a gross , all of those are just a short hand for 20, 12, or 144, respectively. No, one mole isn’t equal to on particle. I never said that at all. As I pointed out earlier, Avogadro didn’t even know the definition of “his” number. He used “equivalent amounts”, not even a mass unit. Moles, as a concept, predate Avogadro’s number and was originally used as mass of something.

You seem to be guilty of the same assumption. Just saying “moles of gas” goes over most people’s head. Saying number of particles…even if that number is almost unimaginably large…is easier to understand. I do a lot of explaining of concepts to non-technical people as well. I tend to keep the terminology as simple as possible. If people understand the terminology, I would hope that they can see the value of the idea of keeping things simple.