The specification discloses a tire inflation pressure regulator facilitating precise tire inflation. The regulator includes a body, a two-position valve within the body, and a rotational lock. The body includes an air inlet, an air outlet, and an air vent. In one position, the valve directs air from the air inlet to the air outlet when the tire pressure is below a preset level; and, in a second position, the valve directs air from the air inlet to the air vent when the tire pressure exceeds the preset level to prevent overfilling. The valve moves rapidly between the two positions, and is unstable between the two positions. The valve includes a regulator enabling the preset level to be adjusted. The rotational lock enables the regulator to be screwed onto a tire stem, but prevents removal of the regulator from the tire stem without a key.