I'm trying to determine the diameter of several automobile inner tubes (ranging from compact cars to semis); as in the diameter within the tube itself (possibly the "width", or even circumference of the tube). I'm referring to the measurement on the dotted line displayed in red on the poor illustration below (the part that looks like stitching on a football).
I know it's an obscure request, but I can't seem to find a size chart or a reference to the measurement in any online guides. Any advice on how/where I can gather this info (short of calling a bunch of vendors)?
Note: I'm working on an online calculator that determines cubic inches within inner tube sizes.