sorry i was wrong, hereis the answer:
I'm checking out 26 x 1.75 - 1.9 tyres for long distance touring. It seems
to me, after several weeks reading catalogues, reviews, emailing
manufacturers, and so on, that the best is Schwalbe Marathon XR, with a
couple of the Continentals possibly in the running, and one or two others,
including Vredestein. And they've thrown a spanner in the works - temporary
I hope - because they mention skinwall and gumwall, terms I hadn't come
across before. According to Vredestein:
Gumwall: Here the tread compound runs all over the tyre and around the
sidewall. These are the traditional tyres suitable for normal bikes.
Skinwall: Only the top surface of the tyre carries a tread compound. The
sides are a canvass carcass. These tyres are lighter and give a comfortable
ride.
Sheldon Browne says something about different tyre makers do BOTH to make
the sidewalls more flexible and improve rolling resistance. But goes on to
say: "It is not clear to what extent this makes a difference."
So my question is: is there a difference in strength? Is a gumwall (no
longer gum I assume from Vredestein's comments, but tread rubber) stronger
because the tread compound covers the sidewall? Do all manufacturers still
make gumwall and skinwall tyres? Would gumwalls be best for touring?
Any comments appreciated.