Subject: Making a Tubular Tire
From: Jobst Brandt
Date: December 23, 2002
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 fora high-quality tubular, that binder is latex rubber.
Fabric for tubular is made on a cylindrical drum about 2m long and 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 0.4-0.8 mm 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 20x40 mm 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 a 20-30mm 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 of 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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