A tire pump includes a passive air pump which is attachable to a component of a vehicle wheel assembly. The vehicle wheel assembly has a vehicle wheel, a tire valve stem attached to the vehicle wheel, and a tire mounted on the vehicle wheel and containing a gas. The passive air pump has an air inlet in direct fluid communication with the atmosphere and has an air outlet in direct fluid communication with the gas in the tire. The passive air pump is operable by transient pressure pulses of the gas in the tire to suck in an air volume from the atmosphere through the air inlet after a present one of the transient pressure pulses and to pump at least some of the sucked-in air volume through the air outlet into the tire during a future one of the transient pressure pulses.