someone wrote:

I didn't see a cross section on that web site. Â*Can you direct me
to one?

Here's the only picture I've found of the Challenge "Open tubular"
ti

http://tinyurl.com/562n9m

Here's my favorite description of these tires (marketing, ya gotta
luv it!)

"The Challenge Criterium Nerone Clincher is a handmade open tubular
that rides… like a tubular. Like a Clement tubular. Clement
tubulars. Those two words used to leave racers speechless. The
Criterium Seta was considered by many the acme of quality, the tires
you saved for race days, the tires that were stored covered and
airless for hopes of extending their useful life, the tires you
lovingly washed after each race, air dried, and then packed away
again.

Clement was bought by Pirelli and they moved everything to Thailand.
Rubber comes from Thailand, so they, and many tire makers, figured
they'd save money by making tires near the source. And, like many
conglomerates, Pirelli realized that the bike world is not a huge
business. They folded the Clement operation.

Like a phoenix, Challenge tires rose from the ashes of those Thai
facilities. Between the Italian distributor and the Thai
manufacturers, they resurrected the tires. Like the good old days,
the tires are still handmade. Also, like the good old days, the
legendary tread is still glued by hand to the casing after the
casing has been tensioned. Many believe that a tread made separate
from casing rides better and with less rolling resistance because it
doesn't get deformed by the inflation of the tire.

The Criterium Nerone Clincher utilizes the same tread as both the
legendary and contemporary Criterium Seta. Longitudinal ribs down
the center, with herringbone on either side. In keeping up with the
times, Challenge offers the tires both as tubulars and open
tubulars. "Open" meaning the casing isn't stitched to itself like a
sew-up, i.e. an open tubular is a clincher. Challenge has also
eschewed the cotton casing for polyester. The casing is still
corespun, resulting in a thin, light, flexible case that is
super-supple. The thread count is 300 threads per inch (TPI), which
in cycling circles is considered a fine casing. Also keeping up
with the times, the sidewalls are colored black (Nerone) instead of
the traditional tan (or "natural").

To give the tire better flat protection, a thin 300TPI corespun
polyester belt, the same material that makes the casing, is glued
above the casing and below the tread. It is also glued on when the
casing is under pressure. They call this their Puncture Protection
System (PPS), giving a little more protection under the tread while
leaving the sidewalls thin and supple.

The Challenge Criterium Nerone Clincher is an open tubular design.
The tire measures 700 x 23mm wide. It has Challenge's Puncture
Protection System (PPS). The casing is corespun polyester. The
beads are made from Kevlar. The tire casing has 300 threads per
inch (TPI). The tire has a Black tread and Black casing. The
weight is 210g."

Come on, all-black, 300 TPI, 210g, and a Puncture Protection System
(PPS), what's not to like?

What is this "core spun" jargon, an how do they come upon 300 TPI?
That requires a thread of 0.00333" diameter and makes sidewalls 0.070"
thick. That's the thickness of a couple of sheets of copier paper.

Jobst Brandt