Monday, July 30, 2007

Tubulars: Part II, Repair


Tubular tires can be repaired, I have done it often, but it is a lot of work. The first obstacle is pulling the base tape away from the stitching.

This used to be an easy matter, but I’ve noticed in recent years with modern adhesives the base tape seems to be permanently bonded to the tire. What I do is pick at the edge with my thumb nail and try to lift just enough of the base tape that I can grasp it with a pair of pliers.

The object is to try to pull the base tape away from the area where the puncture is, but leave it in one piece attached to the tire. In reality, what will probably happen is the base tape will tear off in a short piece.

You will notice this is what happened with the tire I opened up to take these demo pictures. Not to worry you can still glue it back in place after the repair. The next important trick is to find exactly where the puncture is, and only cut about 2 inches (50 mm.) of stitching. An Exacto Knife is the perfect tool for this job.

Under the stitching, is a thin fabric strip or membrane that is lightly stitched to either edge of the outer casing. This strip of fabric is there for two reasons. It holds the inner tube in place while the outer casing is being stitched during manufacture. It also prevents the thin latex inner tube from chafing on the stitching.

Carefully cut the stitching on one side only of this fabric membrane, and pull it to one side to reveal the inner tube. (See picture, below. The fabric membrane is white, the inner tube is green.)


Pull the inner tube out in a loop and the puncture can be patched in the usual way. Before you put the tube back in place, inspect the inside of the outer casing for any sharp objects sticking through that could re-puncture the tube. (This is standard practice with any puncture repair.)

Also, inspect the outer casing for damage as shown in the next picture (Below.) In this case, it will be very important to glue a piece of canvas on the inside, because with 120 lbs plus pressure in the tire, there is a good possibility of a blow out later. Notice I use a piece of rolled up cardboard to hold the inner tube out of the way while I glue the canvas in place.


Canvas can be bought from any fabric store, and any proprietary brand of contact adhesive is good for gluing it. Follow the adhesive instructions, usually you coat the canvas patch and the area inside the tire casing, allow to dry 10 or 15 minuets, then stick the patch in place. Allow it to dry thoroughly (Preferably overnight.) before you put the tube back inside.

There is no need to re-stitch the fabric membrane back in place as long as it is put back over the inner tube, between the tube and the stitching. It will stay in place because you have only opened up two inches or so.

Sewing the tire up again is the biggest chore. You need a sail-makers needle, which is tri-angular rather than round in section. If you buy a proper tubular repair kit, it will come with one of these. (Google: Velox tubular tire repair kit.)

You will need a metal thimble to push the needle, and I use a pair of needle-nose pliers to pull the needle all the way through. If you managed to repair the puncture by cutting only two inches of stitching, you will be glad you did when it comes time to sew it up again.

Try to use the original needle holes to re-sew if you can, and use the same original cross-stitch pattern. If you open up more than two inches of stitching there is a possibility you will not re-sew the tire straight, and you will have a twist in it.

Glue the base tape back with the same contact cement used for the canvas patch. If there is a cut in the rubber tire tread; glue it with the rubber cement that comes with the repair kit. Allow the cement to dry overnight before inflating the tire.

This is part 2 a three part series; here is a link to part 1, and part 3.


8 comments:

gwadzilla said...

I am part of the disposable economy

I rarely even patch a tube

gwadzilla said...

wonderful blog...

I will have to come back
just about time to slide down the dinosaur

I noticed you are from Charleston

do you know Peter of SC Bike Law?

give him a shout and say hello if you see him

if you do not know him

I think you should chase him down

he may appreciate your ideas

gwadzilla said...

http://www.scbikelaw.com/

Anonymous said...

Reading this reminds me just how much biking has changed to make recreational-commuting cycling more appealing to a broader spectrum of riders. Clinchers, patch kits, QRs, CO2 cartridges, indexed shifting, etc. have combined to make repairs and riding so much easier.

I dug out a couple of my old tubs and one has a leak. I'll have to update my repair kit and follow your instructions. If unsuccessful, I'll have to contact one of my heart surgeon friends for more advice.

One of the more difficult problems I use to have was re-sewing the casing and inadvertently putting a few extra holes in the tube. Using extra canvass is an interesting option and definitely simpler.

I still want to know about sizes and where you shop to so I can buy a few extras when I don't have the extra hours to spend on repairing those leaks! There is so much street construction around the city that flats are a weekly occurrence.

Great pictures and thanks for taking so much time and effort in helping the biking community to get a little extra pleasure!

Jack

Dave Moulton said...

Jack.
Email me dave[AT]ProdigalChild.net
Dave.

VintageSpin said...

One has to have the desire to fix tubulars, from there it’s a learning process that may frustrate some. The base tape is the biggest problem: they use “permanent” glue now apparently for liability issues. I use fixed tubs only for spares, not regular riders.
I get about two flats a year. Most of my sew-ups wear out before they flat: check them for cuts in the tread and sidewalls that can lead to blow-outs (save some old ones to cut boots out of).
Kevlar lining helps modern sew-ups resist flats; and rubbing your tubulars often keeps them clean-many riders don’t learn this after switching from clinchers.

Mark Worden said...

I have recently gotten into tubulars with two older bikes I bought at garage sales (An 84 Bianchi and an 81 OLmo) that had tubular weel sets. One had a flat and I was determined to fix it found it to be a pain, but somewhat satisfying when I got done re-sewing it and it held air at 110 psi and road as good as before. I found that one had to bee carefull to keep the tread centered properly on the re-mount to ensure the tire road true. I bought a new set of Rallys for the other bike. I like the "aura" of riding tubular and always carry a spare tire rolled up under my seat too!

eleavitt59 said...

I've fixed many flats on tubulars. Can you repair one after you have used the new fix a flat. Better yet. Would you ever have to.