Weight of air in a bicycle tyre

Hi,
I work in a bicycle shop where we were discussing low weight parts, when I wondered: how much does the air in a tyre weigh? Attempting to calculate it, I've got a bit lost and need help. The question, clearly defined:

How much does the air in a typical mountain bike tyre weigh when inflated to 40psi?
Measurements:
> Tyre/rim = 26" circumference,
> Tyre/tube diameter = 1.95"
> Wheel diameter = 22"

Thanks in advance
Hans

[JohnS]

Originally Posted by Unregistered

Hi,
I work in a bicycle shop where we were discussing low weight parts, when I wondered: how much does the air in a tyre weigh? Attempting to calculate it, I've got a bit lost and need help. The question, clearly defined:

How much does the air in a typical mountain bike tyre weigh when inflated to 40psi?
Measurements:
> Tyre/rim = 26" circumference,
> Tyre/tube diameter = 1.95"
> Wheel diameter = 22"

Thanks in advance
Hans

I'm quite unable to do it in Imperial units, so converting as required.
Avg diameter of centerline of tube 24 in or 0.61 m
Diameter of tube: 0.0495 m
Volume of tube = (pi/4)*0.0495²*0.61 = 0.00117455 m³ (or 1.17455 L)
At atmospheric pressure, air is about 1.2 g/L. At 40psi/14.7 psi, about 2.72X that or 3.265 g/L.

So 3.265 g/L x 1.17455 L = 3.8 g
(many guard digits in intermediate calculations, rounded sensibly at end)
Above is at 25 °C and varies with temperature as lower temperature air is denser.