Courtesy of Jobst Brandt on the excellent Sheldon Brown website:
Opening the Tire
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.
Seam Ripper and Triangular Needle
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.
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 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 using a razor blade to a thin feathered edge 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 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.
Valve Stem Replacement
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 cost 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 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 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 the Tire
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.
Gluing Tire to Rim
For road tires, that are intended to be manually mounted 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 un-glued 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.
Mounting a Tubular
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.
Also from Yellow Jersey with pictures:
Mark the injury first
Then remove the tire and peel back the base tape
Cut some stitches
Pull out the tube
Clean the surface. I use alcohol but any volatile solvent is better than sandpaper. Keep your fingers off the clean surface
Wet the area with cement but not more than enough to wet the area. Allow it to dry which takes about a half a minute.
Press the patch down on the cemented area firmly. Now you no longer have a flat!
Talc keeps the extra glue from sticking the tube to the tire. It’s not absolutely necessary.
Stitch the tire in the same holes as the original stitches. Knot the ends of your repair. Keep the stitch tension even just like in clothing. I tuck the ends under the stitches, some people trim them at the knot.
Wet the bottom of the rim tape and the repaired area well with latex solution. This stuff soaks in fast so it is hard to use too much. Slather it all over.
Press the latexed rim tape back where you found it. Coat the edges with even more latex solution
Glue the tire as you normally do- spread the cement from side to side but not inside the nipple wells. Re- mount the wheel in the bike, upload the photos and ride home!
How hard is it to patch a tubular? I have a couple that I punctured when they were brand new, and it seems such a shame, not to mention a lot of money out the window, to throw them away, but all of my buddies laugh when I say I want to patch them.
If those are slow leaks, put Stan’s, Caffelatex, or another liquid latex sealant inside (remove the valve core to do it), and call it good. If they can’t be sealed that way, think about what you intend to do with the tire before proceeding.
In the early 1980s, I spent countless hours patching tubular tires, often while sitting in the car on the way to distant races. But we were creating training tires, since there were no decent clincher tires and rims available then. Now that everyone trains on clinchers, patching tubulars is rare.
Tubulars may arguably still be the best tires for racing, being lighter, requiring lighter rims, and being able to hold tremendous pressures because of being sewn together (the high air pressure reduces the rolling resistance of the tire on the road). However, even though tubulars are expensive, it makes no sense to patch a racing tire, because you invest too much time, energy, and money competing in races to run the risk of getting a puncture because of a weakened tire.
If for some reason you still wish to patch a tubular, here are the steps involved:
- Remove the tire from the rim.
- Pump up the tire to 70 psi (50psi max for a cyclocross tubular), and find the leak by submerging the inflated tire in a bucket of water, continuing to pump as need be if it loses air too fast. If you’re lucky, air will come out through a hole in the tread. In the case of a pinched tube, though, the air may seep out through the casing randomly at the stitches, and be hard to localize. See the next step for help.
- In the region 2 inches on either side of the puncture, peel away the base tape covering the stitching. If you were unable to precisely locate the hole, try submerging the inflated tire now to watch the bubbles coming out through the stitching. Peel more base tape back if necessary until you are sure that you have exposed the stitching at the hole.
- Deflate the tire and carefully cut the outer layer of stitching threads for an inch or so on either side of the hole. Pull the casing open in that spot, and pull enough of the tube out through the hole to find and access the hole(s) in it.
- Patch the tube as you would a lightweight clincher tube. Use the same type of recommended patches.
- Push the tube back in place, and sew the opening in the stitching closed by hand. I recommend using a needle for leather with a triangular cross-section tip and braided high-test fishing line. Stitch one way across the opening, turn the tire around, and double back over the stitches again. For obvious reasons, be careful not to poke the tube. You may need a thimble to push the needle in and a pair of pliers to pull it out on each stitch.
- Inflate the tire to 70 psi or so (50psi max for a ‘cross tire) to make sure all of the leaks have been patched.
- Deflate the tire and coat the peeled-back section of base tape and the exposed stitching area with contact cement. Barge Cement (originally made for shoes) works well. Wait 15 minutes or so for the glue to set, and carefully stick the base tape back down over the stitching. (If the tape stretched when you pulled it loose, it’s permissible to cut it and overlap the ends.)