Why Do Tires Lose Air When Sitting?
Tires lose air for a couple of reasons. One is underinflation of the tires and another is through a natural process called permeation. Tires should be checked briefly every week to ensure proper air fill.
Underinflated tires become hotter when driven or ridden on than properly filled ones, which may lead to tire failure. It also lets the air out much faster than with normal pressure, both while active and while resting.