My bicycle was simply sitting at rest indoors when it exploded. A slit about ~6mm long was in the tube. I thought it might be too big to patch, but I happen to have some quit big patches to try. I cleaned the area w/denatured alcohol then roughened the surface w/the sanding tool. I covered the whole patch footprint area with rubber cement. Around 90 sec. later applied the patch and lightly clamped it down. About 5 min later: installed the tube and inflated to 4.5 bar.
Couple min later it exploded again. As the image shows, it blew exactly along the line of the original slit. AFAICT, I could not have applied this patch better. That is, the air went through the patch instead of around it.
Why did this happen? The patch is thicker and harder than the tube. So if the adhesive does its job well, then I would expect the patch to be stronger than the rest of the tube. The elasticity is lower in the patch, so I suppose that must be the problem.
So I have to wonder: would it be more or less effective to cut previously damaged spare tubes to use for patching, instead of a patch? I wonder if larger holes need patches with more elasticity.
Rubber cement vs. contact glue
Patch kits include a tiny tube of “rubber cement”. The instructions say to wait 3 min before applying the patch. That’s similar to contact glue instructions. The only difference is contact glue instructions direct us to glue BOTH surfaces then press them together a few min later, whereas the repair kits never say to put glue on the patch (why is that?).
Are the two glues chemically different? I ask because it may not make sense for me to buy another patch kit when I happen to have a very big tube of contact glue for shoe repair.
Why did this happen?
I suspect the real reason this happened was because
- Too small inner tube. The tube around the patch doesn’t stretch enough and causes extra stress on the patch. Inner tubes are rated for specific tire diameter and width
- There’s some spike still in the tire (doubtful since it took 5 minutes to blow)
- Shit quality or too old patch, dried up
Can’t answer the glue question, but can see that didn’t fail so that’s nice
There’s some spike still in the tire (doubtful since it took 5 minutes to blow)
There never was a road puncture. Someone gave me this bike, so I don’t know the history. It came with a flat tire. When I removed it, the tube was twisted in 1 place. Right where it was twisted, there was a hole. I patched it. Then another blowout happened on the other side of that same originally twisted section. Then again. I have three patches on one segment covering nearly that whole diameter. That rubber is bad in that one spot, but that’s not where the current issue is. All those blowouts happened w/out riding. Often just hours after inflating.
Then the blowout I’m talking about happened on a good part of the tube, without puncture. It’s on the inside, but there is decent lining on the rim, thus not from a spoke. But because it’s on the inside, there is an air gap between the rim and the tube. Though I suppose the tube must be forced into the valley of the rim.
It’d be fair to say the whole tube should be tossed, as it could be quite old for all I know. But the patch seems like new… like it’s in a good state. This is what surprised me… that the patch itself failed.
I think what they were getting at is its sounds like there’s something sick inside the tire wearing on the tube??
Ah, I’ll have to check that. That happened to me recently. I installed a new tube, got a hole, patched it, then got to the other side town before it went flat. And I found a piece of glass likely from a beer bottle embedded and hidden in the rubber of the tire.
My post is 4 months old so I wonder if it was the same tire. I probably need to inspect all my tires quite closely. It could be the same glass shard and tire or a recurrance of the same thing.
It doesn’t look like the patch bonded to the tire. I’m guessing a bubble formed between the patch and the edges of the hole. This led to a catastrophic failure.
The rubber cement used in tires is used because it’s basically rubber suspended in a solvent. When the solvent evaporates it leaves the rubber behind which bonds the two sides together to make them one structure. I don’t think the same failure will happen with rubber cement.
Edit: a word
I don’t think the same failure will happen with rubber cement.
To be clear, I used the rubber cement that came with the patch kit. I have not tried using contact glue (which may¹ even be the same thing). But these tiny tubes that come with the patch kits are more costly per unit than contact glue. Now that I am almost out of rubber cement, I’m considering using contact glue for the next patches.
¹ I cross-posted to [email protected] in case a chemist has the answer.
Ah, in that case I’m not sure. Might be like the other commenter said and the patches are either too old or too large. If you have an old tube maybe try the contact cement first on one of them to make sure it works before trying it on the one that matters?
Looking at the patch it is not glued down well. The edge should be completely flatly joined with the rubber all the way round and at the edges.
If it isn’t glued correctly there then I’ll bet it wasn’t glued correctly over the original puncture. Usually with poor uneven gluing the air would leak out from one of the patch edges. The patch has failed this time though.
However I wouldn’t rule out some kind of abrasion on inflation. Whenever you get a puncture try to work out where the corresponding part of the tyre or wheel is (wheel in your case) and carefully feel the area with your fingers for roughness/sharpness. I’ve repaired a number of punctures where I couldn’t see anything initially but after feeling I realised there was a tiny sharp flint, piece of metal, etc that was just protruding enough to damage the inner tube.
Finally on the contact vs rubber cement. Use rubber cement. It is the correct adhesive for the job and as already said it is a solvent based bond so melts the rubber together a bit. Contact adhesive just creates a layer of adhesive between the two surfaces.
Silly question, but why patch a tube? Tires i get, if you shell out $60+ for a tire, replace the tube and patch the tire to keep the crud out. But tubes are comparably cheap and since they are the only thing that needs to hold a seal why not spend a few more dollars than you spent in the patch kit for a new tube?
That would get costly over time. A new tube costs ~€3.50. A patch kit normally costs ~€2.50 and typically has a dozen patches. I got lucky and found a kit with like 40 or so large patches for about the same price. The patches could probably be cut in half. You can also carry a patch kit on long trips using less space than a spare tube.
