Daniel Boone Cycles, Inc - The Flying Wheel.

You want it, BOONE'S has it!

Bikeschool


What's the procedure for tubular tire repair?

From: Jobst Brandt

Opening the Tire

To patch the tube, you must get into the tire and requires opening the casing by peeling the base tape back and unstitching the seam. If this is a seamless tire, chuck it. There are two types of seams, zipper stitch (using one thread) and two thread stitch. The zipper stitch is identified by having only one thread. It appears to make a pattern of slanted arrows that points in the direction in which it can be 'unzipped'. Never open more tire than is necessary to pull the tube out of the casing. Remember, the tube is elastic and can be pulled out of a three cm long opening pretty well. Even if there are two punctures not too far apart, the tube can be pulled out of a near by opening. If you must insert a boot, you'll need to open about 6 cm or about the length of the boot and then some.

Base Tape

Never cut the base tape because it cannot be butt joined. Always pull it to one side or separate it where it is overlapped. (also: Don't cut the tire seam, pull out the stitches.) When working on the stem, only unstitch on one side of the stem, preferably the side where machine finished. Use latex to glue down loose threads on a sidewall cut. Paint the exposed casing zone that is to be covered by the base tape and the base tape with latex emulsion, allow to partially dry and put the tape in place. Put the tire on a rim and inflate hard.

Zipper Stitch

Cut the thread at some convenient place at the upstream end of the opening and, with a blunt awl like a nitting needle, pull out a few stitches in the direction the stitch pattern points. Once you have exposed a length of thread, you can pull the stitching out like a zipper. When you have opened enough, take the loose end and run it through the last loop that has not yet been pulled to lock the zipper. If you think the thread is good enough, don't cut it off but use it to re-sew the seam.

Two Thread Stitch

One of the threads makes a zig zag as it locks the other thread where it penetrates the tire casing. Cut both threads near the middle of the opening and, with a blunt awl like a nitting needle, pull out a the locking thread in both directions. The locking thread is the easier one to pull out so remove as many stitches as you'll need to get into the tire. The other thread pulls out like a zipper. Tie a square knot with the loose ends at both ends of the opening and cut off the rest.

Patching

Patch butyl (black) tubes using patches from a bicycle patch kit.


To patch a latex tube make patches from an old latex tube that are fully rounded and just large enough to cover the hole plus five mm. For instance, a thorn hole takes a 10 mm diameter patch. Use Pastali rim glue wiped thinly onto the patch with your finger. Place the patch on the tube immediately and press flat. Latex will pass the volatile solvent allowing the glue to cure rapidly with good adhesion to the tube.

Casing Repair

Repairing tubular tires requires latex emulsion. You can get it from carpet layers, who usually have it in bulk. You must have a container and beg for a serving. If you are repairing them you probably ride tubulars, and therefore, will have dead ones lying around. The best tubulars generally furnish the best repair material.

Most cuts of more than a few cords require a structural boot. For boot material, pull the tread off a silk sprint tire, unstitch it and cut off the bead at the edge of the fold. Now you have a long ribbon of fine boot material. Cut off a 50cm long piece and trim it to a width that just fits inside the casing of the tire to be booted from inside edge of the bead (the folded part) to the other edge.

The boot must be trimmed to a thin feathered edge so that the tube is not exposed to a step at the boot's edge, otherwise this will cause pinholes in a thin latex tube. Apply latex to the cleaner side of the boot and the area inside the tire. Insert the boot and press it in place, preferably in the natural curve of the tire. This makes the the boot the principal structural support when the tire is again inflated. If the casing is flat when the boot is glued, it will stretch the casing more than the boot upon inflation. After the boot dries, and this goes rapidly, sew the tire up.

Tube Replacement

To replace the entire tube, open the tire on one side of the stem, the side that seems to be easier to re-sew after the repair. Open about eight to ten cm the usual way and pull out the old tube by the stem locally. Cut the tube and attach a 1/16" thick nylon cord to the loose end of the tube to be pulled through the casing as you pull the old tube out.

Cut the "new" latex tube about 5 cm away from the stem, tie the cord onto the loose end and pull it gently into the casing. Dumping some talc into the casing and putting talc onto the tube helps get the tube into place. With the tube in place, pull enough of it out by stretching it to splice the ends together.

Splicing the Tube

This procedure only works with latex tubes. Overlap the tube ends so that the free end goes about one cm inside the end with the stem. With the tube overlapped, use a toothpick to wipe Pastali rim cement into the interface. The reason this MUST be done in place is that the solvent will curl the rubber into an unmanageable mess if you try this in free space. Carefully glue the entire circumference and press the joint together by pressing the tube flat in opposing directions. Wait a minute and then gently inflate to check the results. More glue can be inserted if necessary if you do not wait too long.

Sewing the Tire

Sewing machines make holes through the bead that are straight across at a regular stitch interval. For best results, you must use the original stitch holes when re-sewing. Get a strong thread that you cannot tear by hand and a (triangular) needle from a Velox tubular patch kit (yes I know they are scarce). Make the first stitch about one stitch behind the last remaining machine stitch and tie it off in a slip knot.

With the beads of the tire pressed against each other so that the old holes are exactly aligned, sew in a loop stitch pulling each stitch tight, going forward two holes then back one, forward two, back one, until the seam is closed. This is a balanced stitch that uses one thread and can stretch longitudinally.

Now that you know everything there is to know about this, get some practice. It works, I did it for years.


Back to Bikeschool



Validate this page

Site by Keetek Digital
Hosted by Mossweb
Friends of BOONES

Copyright © 1999-2012 G. Boone   All Rights Reserved