I'll be explicit. Let's say you go out for a ride in winter and it will be 0C all day, what pressure do you put in your tire. Now it''s summer, the temp is 30C (same tires, same combined weight of you and the bike as in winter), what pressure do you use now?

very simple. The same presssure! Because the guage reads air pressue at ambient temperature.

whatever temperature it is, the guage reads the pressure at that temperature.

/markp

i.e., no temperature dependence on optimum pressure.

by about 5 psi, that's how so.

On hot summer days not only is it hot in the air like say 95 degrees, the blacktop can be around 140 degrees on a windless day with direct overhead sun. So tires can get quite hot, and when that happens up goes the psi from the heat. If you have a modern car with tire pressure read out from all 4 tires, you can see that when setting in the garage the tire heat is pretty low, but take out onto the highway and those readings slowly go up, your bike tires are doing the same thing just not as much because you're not doing 80 mph.

You're a little late to the party. See post 27.

There's one scenario where you might keep temperature in mind. If you pump up the tires in an indoor environmentally controlled room, then take the bike out into very hot or cold weather, it could be a factor. Air conditioners and heaters are real things. Obviously, if you fill your tires with 72 degree air, and then ride in 90 degree heat, there will be some pressure increase. Don't know how noticeable it might be, but if you're one of those super high pressure guys, use outdoor air.

I run around 60psi on my 28C GP5000s, which is basically what the calculators suggest for my bike's system weight (88kg rider plus 9kg bike). It's a great compromise pressure between speed and ride comfort, and most certainly doesn't feel at all sluggish to me.

I'm pretty sure he doesn't agree with post 27, they're saying very different things.

With Michelin AirStop butyl tubes (80 gm tube weight), my tires lose about 0.5 psi per day. Is your pressure gauge that accurate or do you have a slow leak or latex tubes?

.5 psi per day is about right. I ride every other day normally. So that's about 1 psi.

And yes, I do pump them up every time I check them. I use the gauge on the pump, so since it's already connected. I'll give the pump a stroke or two to top off the tire.

Don't know if the gauge is accurate, but it is consistent. And the graduation marks are sufficient and large enough so that I can easily inflate them to within a precision of .5 psi.

Only 1/2 psi a day? Are we talking about thin 700x 20 to 28c sized tubes? I use on average 100 gram tubes and for the last 40 years or so I average about a pound to two pounds a day depending on the thickness of the tube and the manufacture, maybe heavier 130 plus gram tubes would lose 1/2 psi a day, I know my touring bike that uses a 35 to 45c tube loses about a pound a week, not sure what the weight of those are. Of course latex tubes lose a lot more at around 30 psi a day if I remember correctly.

Oh, my how complicated PSI can become.

I realized I was putting too much thought into this when I measured what I considered good enough to finish a ride after a roadside flat, and it was a full 40 psi lower than I typically ride at. Basically, it really doesn't feel much different. In that context, obsessing about 5 pounds margins either way seems a bit silly.

Earlier this week, I finished a 93 mile ride (about 1/2 on gravel) and found my rear tire was at 20psi instead of the 37psi I'd started with. I hadn't noticed a thing, and in fact was pretty surprised by how fast I was riding for the last 20-30 miles of the ride. Three possible lessons:
1. Tubeless works, since I obviously punctured and didn't even realize it.
2. I should probably be running lower psi.
3. Obsessing over tiny differences is pretty silly.

I'm full of PSi!

Apparently is so complicated for some people that it's impossible for them to get it right without going on internet....How did people inflate tires before internet was invented ?

Improperly.

Remember, that was in the day of higher was better, until the 15% drop thing came along

I've always preferred my tires to be at a slightly lower pressure. Much better more comfortable ride and better traction. I have never inflated my tires to the max PSI that is on the tire sidewall.

Well I must be doing it wrong because even with internet and all the tire pressures dogmas preached out there I still choose to do it my way.

Bless your heart.

If you find people exchanging ideas and opinions on the internet so objectionable, you really don't need to be here.