Tuesday, October 22, 2013

To Patch or Not To Patch? That Is the Question.

Tubes with punctures, waiting to be patched

Early in my zombie-esque return to cycling, I was riding with my older son, a very accomplished cyclist, and he managed to surprise me. We were having something of a bad luck ride with lots of flat tires and he noticed a patch on one of my inner tubes. "That explains it," sez he, "patching tubes never works. You need a new tube." Both of my sons are very wise and I always listen to them carefully when they offer me advice. In this case, however, I was inclined to disagree based on both theoretical and experiential grounds. But as I said, I take them very seriously so I did some online research. As it turns out, the question of whether to patch bicycle tubes is quite controversial. Here is one example of a blog post followed by a discussion on this topic:

An extract from the Bike Noob Blog. I truncated the post and moved up a couple of illustrative comments.

Having given this topic serious reconsideration, I still come down in favor of patching. As I mentioned in an earlier post, I worked in a bike shop back in the 1960s. My boss and mentor, who I refer to as BB, firmly maintained that a properly applied patch was at least as strong as the original tube, an assertion I have seen repeated by other experts. That is my theoretical basis for patching tubes. Experientially, I don't know that I have ever seen a patch that I applied properly fail; the patched tube my son disdained was loosing air from a new hole some distance from any previous patch. That said, I both have had patches fail and chosen to discard tubes, and I thought I would add my experiences to the online dialogue on this topic.

A few months ago, I was doing my Braes Bayou ride when I encountered a former colleague sidelined by a flat tire. He was riding the old 27x1¼" tires with shraeder valves, whereas I was riding 700C tires with presta valves, so I was unable to offer him my spare tube, but I did offer to help him patch his tube so he could continue his ride to work rather than walk his bike home. The problematic word was "help." Presumably because he was embarrassed at needing my assistance, he insisted this be a collaborative project and so the patch was not applied with the care I believe is necessary for reliability. Consistent with that, when I spoke with him later, I found that the patch had failed (but not before getting him to work). Even when I am patching my own tube, I don't feel I can do as good a job by the side of the road as I can in my garage, so I always carry a spare tube (typically multiply-patched) as well as a patch kit. If I have a single flat, I replace the tube and patch the old one when I get home; the patch kit I carry covers the rare, multi-flat ride. If I am on a more serious ride (such as a brevet) I will carry two tubes to further reduce the need for roadside patching.

An example of a patch kit I carry. From top to bottom, left to right are Instructions, the box everything fits into, a tube of rubber cement, a grey piece of tubing of unknown function, sandpaper, and a collection of patches.

Implicit in the above is that if patching is to be successful, it must be done correctly. There are many descriptions of how to patch a tube by people much more expert than me, and in general, I find the instructions that come with many patch kits pretty accurate, so I won't try to repeat these instructions in detail, but just emphasize a few key points:
  1. Use only bicycle tire tools to remove the tire from the rim so you can remove the tube. These tools have been designed not to damage the tube, something that is all too likely if you use a screwdriver or other makeshift tool. (This caution applies if you are patching OR replacing a tube.)
  2. Somehow note or mark the tube and tire so that, once you find the hole in the tube, you can inspect the tire in that spot to find and remove what caused the hole. (Note that it is easy to flip the tube so that the tube and tire no longer align.) You actually want to carefully and thoroughly run your fingers along the entire inside of the tire looking for problems, but you want to concentrate on where the hole was. Often, the object will have fallen out so you never will be able to find it, but you want to be completely sure that is the case, because if you leave it in, you will get another flat.  This is probably the most troublesome step, in my experience, and once again, this is necessary whether you patch your tube or replace it.
  3. Once you have removed the tube, carefully inflate it until it starts to swell a bit. Then, inspect it by running your hand over its surface or by running the tube next to your cheek (which is more sensitive than your hand) or by immersing it in water to find where the air is coming out. If you use water, carefully and thoroughly dry the tube. Mark the site of the hole, it will be difficult to find later.
  4. Use sandpaper to thoroughly abrade a region around the hole larger than a patch. Apparently, bicycle tubes are produced by injection molding which causes two problems for patchers, a release agent used on the mold is left on the tube which will prevent the patch from adhering and the mold leaves seams which can prevent the patch from fully contacting the tube. There may be other reasons for abrading as well, and apparently it is important to keep the abraded site free of contaminants such as finger grease; don't touch the abraded spot. I find that it is impossible to remove the seams completely with sandpaper, but that the patches are flexible enough to work anyway. Some experts advise using a razorblade or X Acto knife to cut off the seam, others find this results in cutting holes in the tube. Because I feel like I would be in the latter camp, I have never tried this approach.
  5. Apply enough rubber cement to cover the abraded area. Let the cement dry completely. I think not doing this is the most common mistake people make because it is counter-intuitive, and it is my impression that not letting the rubber cement dry completely will almost always result in a failed patch. It only takes a few minutes for the glue to dry, but do be sure it is completely dry by touching it around the outer edges (away from where the patch will be) to make sure it is not still sticky.
  6. Carefully apply the patch centered over the hole. The dried rubber cement is now a contact adhesive, so you will only have once chance to get this right, the patch cannot be moved.

A marked hole in a tube about to be patched next to the permanent, silver Sharpie, my favorite tool for marking holes.

Not only do I wait until I get home to patch my tubes, I find it is more efficient to do a bunch of them at one time, so I let them pile up and keep a stock of patched tubes to replace those which are newly punctured. The little patch kits, like that shown above, are great as a backup to be carried on rides, but are frustratingly inefficient in the assembly line I use; they contain very few patches, the kit runs out of patches before the rubber cement is exhausted, and with the cost of the box, etc., they end up being fairly expensive per patch. Thus, I was very excited to discover that I could purchase patches in bulk packages of 100. However, I still needed the rest of the kit. I went to a teachers' supply store and picked up an old fashioned bottle of rubber cement and cut a few squares from ordinary workshop sandpaper I had lying around. Here is my production line patch kit:

Interestingly, the bulk patches I purchased are labelled "cold patch." The obvious contrast is to a "hot patch" which I remember from my youth in the 1960s. Hot patches used heat to vulcanize them to the tube being repaired rather than rubber cement. The bike shop where I worked had an electric device which clamped the patch to the tube and then heated it to create a bond. This device was too expensive for teenage riders like me, but later I found consumer grade hot patch kits at Western Auto that contained a simple, mechanical clamp and patches that consisted of a rubber patch attached to a small metal container containing a flammable compound. To use these, you clamped the patch where it was wanted, lit the compound, waited for it to burn out and cool, removed the clamp, and peeled the metal container off the tube leaving the patch. Apparently these have been taken off the consumer market, at least in the United States, due to the noxious fumes they generated and/or other safety considerations. There are contemporary alternatives to the rubber cement patches as well. The first are patches that use chemical vulcanization, apparently using an alternative to rubber cement which uses a different chemistry. I have no experience with these, but the few comments about them I read either compare them unfavorably to hot patches (by retrogrouches) or else argue that they are vastly superior to the rubber cement-based patches I use. The second are glueless patches which have adhesive on the back like tape. I have not tried these either, nor am I likely to. Virtually all the comments about them are negative. My guess is that a lot of people who believe that tube patching isn't reliable have experience with these patches. Apparently, they may not even be marketed as permanent patches, but rather just a way to get home.

Despite my best attempts to do patching correctly, there are times when I do get repetitive flats. Is my son right about patching being unreliable? I do not think so. Usually when I have a flat that will not go away, it is from one of two causes:
  1. The object that caused the flat was still in the tire and I missed it.
  2. The tube has gone bad. This usually happens around the valve stem, and usually I can identify this problem before trying to patch the tube.
People who choose not to patch tubes throw them away at the first puncture, of course. Those who do patch sometimes have limits on how many times they will patch a tube (see, for example, the first comment in the Bike Noob blog at the top of this post.) Because I believe properly applied patches in no way reduce the reliability of a tube, I do not ever discard tubes because they have too many patches. The times I discard tubes are when they have gone bad, as described above, or if they have a slow leak that I cannot find. (I am actually suspicious that slow leaks often represent a tube gone bad rather than a really small puncture.)  Up until now, I have not paid much attention to the brand or quality of tubes I buy. I pick up whatever the bike shop carries, or if I am placing a mail order for something else, whatever the mail order place is selling. I don't recall ever have been given a choice at either bike shop or mail order vendor between higher or lower quality tubes. Recently, I noted that Compass Bike Shop (a local bike shop if you live in Seattle, but a mail order vendor for me) is pushing expensive tubes from Schwalbe, a well-regarded manufacturer of high end bicycle tires with the claim that they are less likely to go bad. I am currently a bit low on tubes and so am tempted to order some of these. They are definitely more expensive than the tubes I have been buying and if they turn out to be less prone to going bad, this will make the economics of patching even more compelling.

MAF Test Results

For those new to this blog, each week I am posting an update of my training results as measured by MAF tests; see my previous posts for explanations of my aerobic training program, MAF tests, and this graph.

I will be discussing my training results in detail in a future post. In my current training regimen, I am only doing one MAF test a week. Thus, there is not a lot new on the MAF test front since last week. That said, I continue to be perplexed by what is (not) happening with my MAF test results.


  1. I would add to step 2 (checking for what caused the flat) - go around the rim and make sure that the rim strip is covering all spoke holes. A rim strip slightly shifted can expose rough edges of a spoke hole which will cause a flat a few miles after changing the tube.

    1. Right you are, Biker Bob! Besides the excellent advice itself, your comment should be a reminder to the readers that I am not an expert on tube patching, that if they want to patch tubes, they should get complete and definitive instructions from someone who is.

  2. I think the little tube in your patch kit is for a Woods valve. http://sheldonbrown.com/gloss_w.html#woods