Has anyone ever noticed that if you ride every day, your tires deflate slower than if you leave the bike alone for weeks without riding? I can go for weeks riding every day, without pumping the tires, and the minute I don't ride for a week, the tires are often totally flat. Why is this?
Al Pres said: As you ride along, the air caught between the tire and the ground is pushed into the tire, replacing the air that has leaked out.
Ricardo commented: I think that the white powder in the tubes works to clog the pores of the rubber. When you ride, that powder is constantly being spread around to fill those pores. When your bike sits idly by, waiting for you to give it some attention, the powder settles down and the air begins to slowly leak out.
Perce said: Not bad! However, I think everyone else is completely wrong!
The real reason is this: The tires are really enthusiastic about riding! As long as you keep riding, they stay pumped up! But when you go without riding for a week, they become really deflated!
El Scriborino said: Actually, it's because they lose muscle tone when not being used, thus they become flabby.
Scruffy reckons: You are probably failing to park your bike with the valves up. If the bike sits around idle, the air eventually stops moving and ends up in the bottom of the tire. If you park with the valve stems near the bottom, the valves may not be able to handle the additional air and will leak.
Phil said: Maybe it's because when you ride, it heats up the tube (due to pressure the rider exerts down and the resistance of the tire on the road), which may cause the rubber material to expand a little bit like a piece of dough rising. If the bike remains cold for many days, the tube material may shrink and permit some of the pressurized air in the tube to escape.
Elvis said: But then how do we rationalise the mysterious "High pressure leak" that only occurs under high-inflation, and disappears when you inflate the tube at a lower pressure and check for holes in a tub of water? These leaks would seem more likely to occur when riding than when not. Can't the tubes get their act together and be more consistent in their behavior?
The Hamster said: The reason that frequently ridden tubes hold air better is because the molecules of air inside the tube are pushed around in a high pressure environment. This produces an increased physical robustness that prevents them from escaping through the rubber pores as easily as their wimpy less exercised brethren.
The great search for truth goes on, with the most astute minds straining their abilities to establish beyond doubt the power of science and intellect in our lives! Perhaps you have some suggestions.