Touring - Why do tubes lose air?

New tube, out of the box. Installed, pumped up to 100 psi, trued the wheel, went to bed. Got ready to ride the next day, checked the tire, 80 psi. I had checked the tire for debris, rim for burrs, etc. prior to installing the tube. I've also noticed this on other tires/tubes as well. Where does it go? Poor tubes? Bad valve? Bad brand? Anybody else experience this?

New tube, out of the box. Installed, pumped up to 100 psi, trued the wheel, went to bed. Got ready to ride the next day, checked the tire, 80 psi. I had checked the tire for debris, rim for burrs, etc. prior to installing the tube. I've also noticed this on other tires/tubes as well. Where does it go? Poor tubes? Bad valve? Bad brand? Anybody else experience this?

They have a certain amount of porosity. Also, perhaps your air chuck removal technique needs honing. I notice that many let out more air than necessary in the way they remove said chuck.

http://www.kenkifer.com./bikepages/humor/air.htm

I HAVE definitely noticed that after installing a "new" tube that it ALWAYS needs to be pumped up again the next day and then they settle in and don't lose as much from there on. I don't know, maybe the rubber on new tubes is so tight that it doesn't fill out all the spaces in the tire at first, but give it a few hours and it stretches out and relaxes and therefore needs more air.

I HAVE definitely noticed that after installing a "new" tube that it ALWAYS needs to be pumped up again the next day and then they settle in and don't lose as much from there on. I don't know, maybe the rubber on new tubes is so tight that it doesn't fill out all the spaces in the tire at first, but give it a few hours and it stretches out and relaxes and therefore needs more air.

I ride every day, and want to ride at a certain pressure. The next day, my tires are not at that pressure regardless of the age/brand/type of tube used. Bottom line: I pump up my tires every day.

I ride every day, and want to ride at a certain pressure. The next day, my tires are not at that pressure regardless of the age/brand/type of tube used. Bottom line: I pump up my tires every day.
I agree, I like to ride at a certain pressure and pump mine up almost every time I ride. Sometimes I go a day or two and don't pump them up if I'm just going out for a casual ride. You are right, ALL tubes lose air and if you notice I said they "don't lose as much" after that very first day, but I've just noticed that the first day they seem to lose a lot more pressure than they do after that. Keep on pumpin'.

It's because of "molecules."

Maintaining tire pressure is frequently recommended to save fuel and increase safety in motor vehicles. Bike tires are smaller, thinner, and pressurized a good deal higher. I am not surprised that I need to pump them up so often.