Why do tires lose their pressure?

Because of permeation (i.e. air seeping through the rubber). Tires lose more air when it's hot outside, although it can also be due to the place where you ride.  more

Because of permeation, i.e. air seeping through the rubber. Tires loose more air in hot weather. CHECK your tires inflation/pressure - WHY? Since air is a gas, it expands when heated and contracts when cooled. As ambient temperatures gets colder, your tires inflation pressure is going down! and conversely As ambient temperatures get warmerr, your tires inflation pressure is going up! The rule of thumb is for every 10° Fahrenheit change in air temperature, your tire's inflation pressure will change by about 1 psi (up with higher temperatures and down with lower). You should check your tires inflation/pressure prior to each trackday event. Anotherwards the morning you arrive at the track you should reset your tire pressure as called for (depending on weather and track conditions). You tires must be checked when the tires are cold, which usually is before they have run a mile.  more

Because of permeation, i.e. air seeping through the rubber, tires loose more air when it’s hot weather, so it’s also partly due to the place where you ride. When should I check my tires inflation pressure? Check inflation pressure at least monthly and before every long trip or race. If Land Speed Racing, before every run. Be sure that the check is done when tires are cold, which usually is before they have run a mile. Now for the Drag Racing aspect of tires. I have been dabbling in Drag Racing for quite a few years now and have found that for my particular application of tire, there is only 1 choice for high horsepower applications. The STICKY MICKEY!  more