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Yes, they can gain or lose pressure as the weather changes.
That said, as long as they've been filled within their specs, they're relatively unlikely to explode even with significant swings if they're just sitting there.
That said, it's still a good idea to check your pressure at the start of every day before you ride and adjust accordingly: Too much or too little pressure can cause all sorts of problems from pinch flats to premature wear to blow outs.
In short, keep the pressure constant, because 8bar will be 8bar in winter and in summer. It's kind of a 1kg of steel vs 1kg of feather type of deal. It's still 1kg.
But if you want the details, yes pressure will increase with temperature, they are directly related. Charles's law state "The absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system." Since in bike tires volume is constant, it's given that pressure is the one to change.
And yes, tires do explode. I had mine explode when bike was left on the sun but it had underlying issue. Under normal circumstances they are usually engineered to withstand normally expected temperatures. Also tires get hotter when they are ridden and they also experience sudden raise in pressure when running over pot holes and similar.
Considering that you need to check tire pressures every 6-12 weeks, I wouldn't worry about the summer/winter difference.
On my bike the recommended pressure is in the 4-6 bar range. so way more than the expected variation from temperature (or day to day pressure).
Something I thought about recently as well. I might be wrong, but is pressure not just a differential from inside to the outside? If it gets warm, air expands inside the tire, but so does the air outside, pushing back. It kinda sounds right, but I don't know.
Atmosferic pressure doesn't change as much as air density with temperature, because its not a closed system.
Actually easier to ride faster in summertime due to less dense air in which the cycler will have to move trough...
This is easy enough to test. Take a tire and fill it. Test the pressure. Let it sit outside overnight on a cold night and test it again. The pressure will be lower.
Consider this, as well: yes, it's about differential pressure, but it's also volumes. "Pressure" is the outward force from all of the molecules in the air bouncing around in a space. As temperature increases, those molecules move faster and bounce more. Since pressure is just us measuring that bouncing, increased temperature increases pressure.
Why doesn't the atmosphere increasing in temp balance it out? Size. The tire is SIGNIFICANTLY smaller. This means each individual molecule only has to go a little bit before it's hitting another wall. Compared to outside the tire, those same molecules bounce off everything, some ricocheting into the tire, and others in whatever random other direction. The change in movement speed of the particles may be the same, but the change in how frequently they're smashing into the tire is different, thus different pressures.
But at the same time, tire itself expands reducing the pressure.
I think the atmosphere can increase in volume when it gets warm because it's not a proper closed system, so the pressure doesn't go up in the same way.
This makes sense. Thank you!
We have a couple of bikes in our garage. In Australian summers it gets to a minimum of 50°c in there. No explosions to date.
Pressure, volume and temperature are all interrelated.
Assuming constant volume; as temperature goes up, so does pressure to compensate. (Alternatively volume can also increase. While tire generally don’t expand much, they do expand slightly, since rubber is… well, rubber.)
Look up the ideal gas law.
But even then your tires won't explode due to temperature induced pressure change, unless you're about to blow them up already when cold.
It's not a bad idea to deflate them if you go through sudden temperature changes but it's important to remember that tires are porous and will slowly leak air over time so it's less of an issue in that direction... you also don't hear about it as much because people tend to bike more in warm weather so it's more likely for you to go long stretches of time without biking when it's getting colder.
So there are quite a few reasons why the deflation problem gets talked about more.
you also don’t hear about it as much because people tend to bike more in warm weather so it’s more likely for you to go long stretches of time without biking when it’s getting colder.
Off topic, but I think it's funny how cycling is viewed in different parts of the world. You look at it as a hobby that is naturally done less in the winter. For me it's just a way to get to work and I still have to work when it's cold, so obviously I'm still cycling just as much. And this is true for a lot of people, the bike rack at my job is almost as full in the winter as it is in the summer.
I don't view it as a hobby but biking in 12 cm of snow with an icy crust isn't realistic. When the snow hits it's the train or bus for me.
Yeah, it's entirely the way the city is design. Biking to work save shit tons of money and time from fuel, traffic jam, and maintenance, and if people are given the choice of doing it safely, a lot will shift into biking.
Another person listed a good graph but yeah, the amount of volume change in air by temperature (assuming normal ‘human life’ ranges) are a matter of just a few percentage points. Any increase in air pressure is undoubtedly nullified by ambient leaks of air and similar in your tires.
You are overthinking it my man. Yes, the pressure does go up, but overinflated tires need to be way way way over inflated to explode. Unless you are a pro cyclist or store your bike in the trunk of your Kar in the Sahara desert... no, they don't pressurize enough to matter.
/not an expert
To do the math, an assuming constant volume, a 30C increase corresponds to around 10% increase in pressure. That's well within the margins of the tyre even if you go to the max rated.
If you then consider deformation and most importantly leakage over several weeks, this is a non-issue.
Overpressure can cause its own issues, it can cause uneven wear. That uneven wear can lead to bald spot that can cause the tire to blow.
Optimal tire pressure should be maintained at all times, not overthinking at all.
Optimal everything should be maintained at all times, yes, of course...
Just a small note: the pressures in this chart are absolute, not gauge. In everyday usage (like talking about tire pressure) we mean gauge pressure - that is, the difference in pressure from atmospheric pressure.
Your overall point is well taken (the change in temperature doesn't matter much), but the numbers will be slightly different. For example, a tire filled to 100 psig (gauge) will reach 106.496 psig at 100 deg F, versus 105.663 in the original chart (assuming 14.7 psia atmospheric pressure).