Innertube Porosity?

On Thu, 29 Dec 2005 21:56:00 -0500, Steve Sr. wrote:

I was wondering if anyone has any information on the porosity of various
kinds / brands of innertubes. By porosity I mean the very slow leakdown
rate that occurs with sound tubes over days and weeks. You know... The
reason you are always topping up your tires to prevent pinch flats.

My current interest is any differences between the regular and
"lightweight" road tubes of the same size. I am also wondering if "brand"
makes any difference as well.

There's certainly a difference, but I've never noted exactly how much. Of
course latex tubes need to be pumped every day. Lightweight butyl tubes
maybe every 3-4 days, and regular tubes once a week or less.
Besides the difference between lightweight and regular tubes, there are
differences between brands. Some are thicker than others.

When I buy tubes, I worry more about valves, and how easily the tube can
be patched. These days I buy only Michelin tubes, because the valves
never leak, the pump seals well, and there's minimal
flashing/seams to interfere with patching. Either the regular
"Airstop" or lightweight models are fine.

Matt O.