Subject: Tubular Tire Repair
From: Jobst Brandt
Date: May 4, 1999
The tire casing must be opened to gain access to patch the tube. To do this, open 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 point 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 a long way from a three-cm long opening. Even if there are two punctures not too far apart, the tube can be pulled out of a nearby opening. However, to insert a boot requires an opening of about 6 to 10 cm at the location of the cut or rupture, about the length of the boot (at least 10cm) and a couple of cm more.
Never cut the base tape, because it cannot be butt joined. Always pull it to one side or separate it where it is overlapped. Do not cut the stitching, because it takes more time to pull out the cut thread than to pull it out in one piece. 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 tape with latex emulsion, allow to partially dry, and put the tape in place. Put the tire on a rim and inflate hard.
A convenient tool, available in the sewing department at most department and sewing specialty stores, is a seam ripper. This and the triangular sewing needle from a Velox patch kit are two highly useful tools for tubular repair, scissors and razor blades being common household items.
Cut the thread at some convenient place at the upstream end of the intended opening and with a blunt awl, like a knitting needle, pull out several stitches in the direction the stitch pattern points. When enough thread is free to pull on, the stitching can be opened like a zipper. When enough seam is open, thread the loose end through the last loop and pull tight, to lock the zipper. Don't cut off the free end, because it is often good enough to re-sew the seam.
One of the threads makes a zigzag 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 knitting needle, pull out only the locking thread in both directions, stitch at a time. The locking thread is the one that is easier to pull out. Remove as many stitches as the opening requires. 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.
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 (tire patch glue also works but not as well) 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.
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 a tubular, you probably ride them, 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, like a glass cut, require a structural boot. With thin latex tubes, uncovered casing cuts will soon nibble through the tube and cause another flat. 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 10cm 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 using a razor blade, so that the tube is not exposed to a step at the boot's edge: otherwise this will wear pinholes in a thin latex tube. Apply latex to the cleaner side of the boot and the area inside the tire, preferably so the boot cords are 90 degrees from the facing tire cords.
Insert the boot and press it into place, preferably in the natural curve of the tire. This makes the boot the principal structural support when the tire is again inflated, after the boot cures. 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.
This depends on the type of tube. Latex tubes and some of the others have a screwed-in stem that has a mushroomed end on the inside and a washer and nut on the outside. These are easily replaced from another tire whose tube is shot. Open the old ruined tire at the stem, loosen the nut, lift the washer and pull out the stem.
Open the tire to be repaired on one side of the stem, preferably the side where sewing ended, the messier side, and loosen the base nut, lift the washer, wet the stem at the tube opening with saliva and twist it until it turns freely. Pull it out carefully and insert the replacement stem after wetting its mushroom with saliva. Tire stores have a soapy mixture called "Ru-glide" or the like to do the wetting but it costs a lot more than spit and doesn't work any better.
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, so that the old tube can be pulled out by the stem. Cut the tube and attach a strong cord to the loose end of the tube to be pulled through the casing by the old tube as you pull it out.
Cut the "new" latex tube about 8-10 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 help get the tube into place. With the tube in place, pull enough of it out by stretching it, to splice the ends together.
This procedure works only with latex tubes. Overlap the tube ends so 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 machines make holes through the bead that are straight across at a regular stitch interval. For best results, use the original stitch holes when re-sewing. Use a strong thread (one 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 with a noose knot.
With the beads of the tire pressed against each other so that the old holes are exactly aligned, sew using 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.
Instead of a hand needle, you might want to invest in a "sewing awl." This is a tool with a hollow handle similar to that of a screwdriver. The hollow handle holds a small bobbin for thread.
It has a chuck that will hold a sewing-machine needle, with the eye near the point. This tool has two advantages over a hand needle:
- The comfortable handle makes it much easier to push the needle through the casing.
- The sewing-machine type needle enables you to duplicate the original stitch pattern.
Sewing awls are available anywhere that sells leather handicraft supplies, such as Tandy Leather.
For road tires, which are intended to be mounted manually and replaced on the road, tires with a rubberized base tape are preferred because these are easily and securely mounted by applying a coating of glue to the rim, allowing it to harden, and mounting the tire to be inflated hard so that it will sink in and set.
Because road tires are intended to be changed on the road, they use a glue that does not completely harden and allows reuse for mounting a spare.
Track tires, in contrast, can be mounted using hardening glue such as shellac or bicycle-tire track glue. This glue is best suited for base tapes that are "dry" cloth. The tire is mounted either with a light coating of track glue on the base tape or unglued onto a good base of track glue whose last coat is still soft on the rim, into which the tire will set when inflated upon mounting. Hard glue prevents rolling resistance otherwise generated by the gummy road glue. Track glue is primarily useful for record attempts where every effort is needed.
The most effective and fastest way to mount a tubular is to place the rim upright on the ground, stem hole up; insert the valve stem of the tire and with both hands stretch the tire with downward force to either side, working the hands downward to the bottom of the rim without allowing the tire to slacken. Try this before applying rim glue on a dry rim, and inflate the tire hard so that afterward, mounting is easier on the glued rim.
Note that inflation pressure causes the tire to constrict until the cord plies are at about 35 degrees. This effect helps retain the tire on the rim in use. Therefore, do not inflate a tire to mount it. Tubulars should generally not be inflated off a rim because this deforms the tire and base tape adversely, possibly shearing the inter-ply adhesion and loosening the base tape and stitching.
Now that you know everything there is to know about this, get some practice. It works, I did it for years.
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