11-18-1998, 11:46 AM
Ok, so this is sort of a stupid question, but It just came up in conversation as to if it is worth letting the ar out of a tire/wheel combo when you ship it?<p>I'm guessing about a cubit foot of air, at 36PSI. <p>Hmm, my high school chemistry/phisics is failaing me and if I think college, I just know I'm going to have to use integration.... HELP<p>There is no prize to the best sounding answer, and for the correct answer, just my admiration and that of of the 2 or three people who read it.
11-18-1998, 12:29 PM
...why not replace the air with helium and make the shipment even lighter!<p>CraigB<br>(always thinkin')
You'll roughly triple the amount (and weight) of air contained in a tire when at 36 psig than at 0 psig.<p>This is learned from the ideal gas law. Air isn't ideal but close enough in this situation.<p>PV=nRT<p>v, R, and T are constants, therefore:<p>P is directly proportional to n<br>n being moles (or mass or weight)<p>When under pressure:<p>You're going from 15 to 51 psi (absolute), roughly tripling P in the equation. Thus you would be tripling n.<p>Find V, solve for n, and you'll have the exact number...<p>AJL<br>98 Passat
11-19-1998, 07:06 AM
Fill one to 36PSI, pop it on a scale, then let the air out.<p>I bet it makes no difference whatsoever.<p>--Greg<br>
11-19-1998, 09:14 PM
The tire displaces ~ 40 liters of air at 36 psi = 135 liters at 15 psi / 22.4 l/mol = 6 mol -2 mol for buoyancy (measurement made in air) =4 mol x 32 g/mol (est MW of air) = 128 grams. 130 grams rounded up.<p>Obviously it's time to go to bed....:-)<p>Steve
Gary @ Ronal
11-20-1998, 05:54 AM
Peaked my interest. Thanks to UPS weight scale we weighed a 17" wheel, then a 17" 225/45/17 tire, mounted and filled it with 42 psi and the weight diff. by our "crude" scale was less than a pound.