The Tire Pump is a hand operated air pump with a built in pressure gauge used to inflate and deflate Tires. The player does not initially own this tool, so it must be purchased from Kali-Gas for $44.00.
With the Tire Pump equipped, the pressure of any wheel and tire can be adjusted, regardless of whether they're mounted to a vehicle or not. Pressing the Left Mouse Button will raise the pressure by one PSI; holding the Left Mouse Button will rapidly inflate a tire. Pressing the Right Mouse Button will lower it by one; holding the Right Mouse Button will rapidly deflate a tire.
According to the sticker located on the driver's side door sill of the Konig, the proper amount of tire inflation is ~32psi; a tire can be inflated above or below this value, but it will adversely affect vehicle handling. Inflating a tire beyond 50 PSI runs the risk of having it burst from the wheel; the tire won't be damaged, but it will need to be reseated back on the rim using a Tire Changer.