That's a new one on me, I'm sceptical, lets see if it makes sense:
Constants, formulae and assumptions:
-The mass of air at 1 atmosphere of pressure is 1.2Kg/m^3.
-Using my own tyres, which are 195/55R15s, and require 2 bar of pressure above atmosphere.
-considering the volume of the tyre to be the volume of the cylinder representing the tyre, minus the volume of the cylinder representing the wheel.
-Volume of a cylinder = pi*radius*height
Calculations:
-Wheel & tyre hight: 0.195m
-Wheel radius: 0.191m ((15" in m) / 2)
-Tyre radius: 0.298m (0.195*0.55+0.191)
-Volume of wheel: 0.117m^3 (3.141592654*0.191*0.195)
-Volume of tyre: 0.066m^3 (3.141592654*0.298*0.195-0.117)
So, at road pressure there are 3 atmospheres of air in my tyres (2 bar + natural pressure), but the tyre full of this air displaces its on volume of air at 1 atmosphere, so we only need to count 2.
Weight saved per tyre by letting them down to 1 atmosphere of pressure (0 bar, 0 psi): 0.079 Kg (0.066*1.2).
79 grams. w00t