GhostRider62

No. I bought new tubeless rims with claims and some tests showing that they are better and safer than others. I checked the claims. Why? I had a double blowout thru debris on the road in September breaking 10 bones in the ensuing crash, so, a blowout isn't necessarily a benign event. I normally sit up and let the air cool me down as part of my braking strategy, so, I have never had a problem overheating carbon rims but I wanted to see for myself.

Iride01 

You still aren't helping me want to make that move to tubeless!

rydabent

This is why some cyclist that run extreme air pressure have tires fail. They start with extreme pressure, and then hot road ways take the pressure way up.

On a car they say for every 10 degrees increase you get another one pound of pressure.

GhostRider62

I have hooked tubeless rims and have not had a flat all year.

The biggest issue for me is lack of tires (supply chain) or the puffy prices if you can find them.

Bill Kapaun

For all of you taking air pressure measurements-
What's the temperature error of the gauge itself?
A bladder type gauge is likely to show higher pressure the warmer the gauge is.
Take a gauge that sits in the glove box of your car. Do you expect the same accuracy in sub freezing temps to 120+ that a car interior can reach?
How many spirits can dance on the head of a pin after lunch vs before?

cyccommute 

I consider 5 psi to be extremely slight. You also have to consider that the pressure fluctuates with impact and/or just pedaling. The impact decrease the volume of the tire which increase the pressure in the tire. If your tire is so sensitive to a 5 psi fluctuation, you probably shouldn’t be riding it anywhere but an extremely smooth surface.

It’s not the size of the temperature increase but the impact. A 2% increase is tiny. If you heat a tire from 32°F to 112°F, the total pressure increase is 20 psi. To get a 5 psi increase in pressure, you need to heat the tire 25°F. That’s a lot of heat for a very small pressure change.

Clyde1820

Good point.

Inherent error of the measuring device plus the increase in tire air temp from usage/roadway, I would think 5-7psi or more is to be expected, depending. (Say, inflating and measuring at 70deg, but riding in 85-90deg on a roadway that's ~125deg or more.)

IIRC, for example, the Meiser Accu-Gage line is rated at +/- 3% accuracy, for the gauge itself.

vespasianus

Might want to talk with the NFL and Tom Brady. Actually, the person you should talk with with is Jacques Charles, but he has been dead for a couple hundred years.

Check your car tire pressure after driving it.

curbtender

I can see what you are talking about, but I doubt he was taking pressure readings while riding, lol.

GhostRider62

Go listen to Josh's podcast after re-reading what I wrote. You have a very annoying habit of twisting **** around. I was specifically talking about the risk of over-inflating hookless rims , the much smaller safety margin of such a setup AND lastly. I do not have hookless rims.

dedhed

https://www.calculatorsoup.com/calcu...al-gas-law.php

79pmooney

If the OP inflated the tires indoors at 70F and it was sunny (late May in North Carolina if I read his location correctly) the pavement could easily be 10 degrees warmer than the thermometer reads. Now, the OP did not say what his starting pressure was so I am going to presume 80 psi for this calculation. So that's 25 degrees hotter. (25+70+491)/(70+491) X (80+14.7) - 14.7 = 1.045 X 94.7 - 14.7 = 98.9-14.7 = 84.2F or an increase of 4.2psi. (5F with the gauge? 0.8F margin of error? Do we ever see better in this world of bicycles? Oh, my guess of a starting pressure affects the pressure change. A higher starting point would raise the gain. In fact, starting at 100 psi yields 5.1 PSI gain. I could do this backwards and tell you your starting pressure if you promise me that 5 psi gain is good to two decimal places. But, my school days are long past and a better grade gets me nothing so I'll pass.)

For the Perfect Gas Law to work, everything must be absolute; ie measured from zero. The added 491 takes Fahrenheit to zero. The added 14.7psi takes the pressure to zero. It must then be subtracted out of the end result so we see the relative pressure we are used to.

And that 10 degree temperature difference due to the sun on the pavement? Well I just rode 30 miles on my rain bike through two light showers. SUn after both. And both times I got to ride through a low, warm cloud of damp air evaporating off the pavement. While I rode with arm warmers, leg wamers and several tees under my spring/fall jersey.

2manybikes

How long is a rope?

Polaris OBark

If your starting temperature (the one where you made your initial pressure reading) was about 60°F, and your initial pressure was about 100 psi, this would be expected for an ideal gas (assuming no change in tire volume).

cyccommute 

Nope. Not Jacques Charles. That gas law relates temperature to volume with a constant pressure. Joseph Louis Gay-Lussac is the one who related pressure and temperature. He also co-discovered boron, discovered that water is made of 2 parts hydrogen and 1 part oxygen, and recognized iodine as an element, among other discoveries.

cyccommute 

Perhaps you should also reread what I wrote. The effect of temperature on a pressure isn’t nearly as large as people think it is. Hookless rims may have a smaller margin of safety but heating the tire isn’t that much of a concern. Heating a tire over a range of 80°F (32° to 112°) results in a 16psi increase. That’s not much of a pressure increase for a very large temperature change. It takes about a 30°F temperature increase to get a 5 psi increase in pressure.

For rbrides, he is finish temperature was 83°. Did he fill the tires at 53°F? I would still suspect some kind of measurement error over a pressure increase due to temperature change.

But your cautions are a bit of a red herring. rbrides isn’t using a hookless system.

Fredo76

I suppose that depends on what a person is thinking. I do know that 40 psi in your car tires at 70 degrees F will mean flat tires at minus 50 degrees. That's more effect than some people would think, I'm pretty sure.

rbrides

Ya got that right!

rbrides

Isn't that the true!

Kapusta

I have not read all the replies, so this may already be mentioned, but when doing gas law calculations, keep in mind that what pressure gauges read (and what actually matters) is NOT the pressure inside the tire, but rather the DIFFERENCE between the pressure inside the tire and outside the tire.

rumrunn6

are you also measuring the tire width w/ a caliper before & after?

regardless, that sounds like an impressive ride! how much water did you use?

cyccommute 

Nope. At -50°F (227K), the pressure would be 30 psi. The tires might go flat because the rubber isn’t flexible anymore and may crack but the pressure wouldn’t be zero. You’d need to condense the air to get to near zero pressure which is -320°F (196°C). The rubber will definitely shatter at that temperature. But notice that the pressure change is only 10 psi.

I’ve done demonstrations with balloons in liquid nitrogen where I can show liquid air (and zero pressure in the balloon). It’s very cool to watch the balloon collapse and a pool of liquid form in the bottom. It’s also very cool to watch the balloon expand as the liquid air boils off.

cyccommute 

Not really. There are many different designs for pressure gauges but all of them are sealed systems that measure the pressure in the tire directly. They don’t compare the pressure inside to the pressure outside. Gauges can be calibrated in absolute pressure (i.e. atmospheric pressure included) and “gauge” pressure (i.e. just the pressure in the vessel) which matters for some measurements but for determining the change in pressure with temperature, either would work. Most every bicycle gauge is going to be measure in psig (psi gauge).

Kapusta

Every pressure gauge that a consumer uses measures relative pressure. Which it should, because that is what matters.

This is why the pressure you read for a tire will increase when you go higher in altitude.

cyccommute 

It measures relative pressure but that’s not the same as measuring the difference between the pressure outside the tire and the pressure inside the tire. A psia gauge measures the pressure in the vessel compared to a vacuum while a psig gauge measures the pressure compared to a standard atmospheric pressure. But there is no physical comparison of the pressure inside the vessel vs the pressure outside during the measurement.

From the standpoint of the Ideal Gas Law, the absolute pressure is important because that law contains a variable for the amount of gas present. But the Ideal Gas Law is the wrong law to use for determining changes in pressure due to temperature. The Ideal Gas Law is derived from Charles Law (V/T=k), Boyles Law (PV=k), Guy-Lussac’s Law (P/T=k) and Avogadro’s Law (V/n=k), where n is the number of particles of gas). Since the volume and the amount of gas is constant, all that is needed is the relationship between pressure and temperature.

You can get to Guy-Lussac’s Law from the Ideal Gas Law but it’s the long way around.

Partly but it’s mostly because the “gauge” part in psig is calibrated for sea level pressure.