8b.26 Making a tubular tire
Description
This article is from the Bicycles FAQ, by Mike Iglesias with numerous contributions by others.
8b.26 Making a tubular tire
From: Jobst Brandt <jobst.brandt@stanfordalumni.org>
Date: Mon, 23 Dec 2002 15:04:39 PST
The tedious but simple process of hand made tubulars is not much
different from mechanized manufacture that automates many of the
steps. Tire casings are made of two crossed layers (plies) of
side-by-side cords that are not woven as cloth. An elastic binder
between the layers holds them together and for the high quality
tubular, that binder is latex rubber.
Fabric for tubular is made on a cylindrical drum about 2m long 20cm in
diameter, with a narrow 45 degree helical slot from end to end. A
single layer of thread (cords) is wound onto the rotating drum from
end to end and coated with latex solution. When dry, the unwoven
cloth is cut along the 45 degree slot with a razor to produce a 20cm
wide sheet (long trapezoid) of diagonal cords lying side-by-side at 45
degrees, held together only by the latex coating.
This band, when folded in half lengthwise, with partially cured latex
to the inside, will adhere to itself, and make a 10cm wide two ply
strip. Both edges of this strip are sheared to a desired casing
width. The ends of this cloth band expose single layer triangles that
exactly match each other when closed in a loop to make a seamless two
ply circular band, the tire casing. An 8mm wide selvage, through
which the tire closure seam will be stitched, is folded, glued and
sewn along both edges of the casing.
A yellow 0.4-0.8mm wall thickness latex tube, much like rubber
tourniquets used in blood clinics, is formed into a hoop with a 10mm
lap joint. A nickel plated brass Presta valve stem, with a 10mm
diameter, rib faced mushroom end, is inserted into a 3mm diameter hole
in the tube at its overlap and where it has been reinforced by a
20x40mm elliptical rubber with fabric backing reinforcement that
prevents extrusion when the nut is clamped. A rib-faced washer is
placed on the protruding stem, secured by a hex nut to produce the air
seal.
After laying the tube in the casing, a 20mm wide band of soft cloth is
sewn to the inside of both edges of the channel shaped casing to
prevent the tube from chafing against the main closure seam. The main
seam uses one of two common tire stitches. The two thread version
appears as an "X" pattern down the middle, while the other uses a
single thread diagonal loop and lock (zipper) stitch, both kinds are
biased and can change length with the casing. The seam is machine
sewn, beginning at the valve stem, and is manually finished when it
again reaches the stem.
A bias weave base tape with a20-30mm overlap near the position of the
stem is placed on a rim and given a coat of latex as is the tire that
is mounted on the rim and inflated. The outside of the inflated tire
is given a coat latex to which the tread that has also been primed
with latex is applied with a little stretch. The tire is complete.
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