Joerg wrote:

:Yup. Standard bicycle tubes are usually junk. Would you accept it if you
:had to pump up the tires of your car every two weeks? Yet most cyclists
:think this is "normal".

Automotive tires have a much lower ratio of surface area to volume
than bike tires. They're also run a lower pressure, for the most
part. So even if the permiability of the two tires were the same,
car tires would lose pressure slower. Of course, automotive tires are
much more impermiable, because they're heavier and thicker (the
inner liner of a typical car tire weighs as much as a bike tire does,
all by itself.)

--
sig 112