What could have caused this puncture!

[Dwn]

Any suggestions from the experts?

I was cycling along today, when the tyre deflated with a very loud bang. It deflated so quickly that the tyre unseated from the rim within the time it took me to stop. Roadside change of tube revealed no obvious damage to the tyre, but a gash in the tube. It had been inflated the previous day and was easily within the suggested limits for the tyre. Any ideas?

 

[si_c]

That doesn't look like the rim was unseated by the inner tube deflating, rather the reverse. A gash like that is caused by the tyre coming off the rim and the inner tube being caught between them. Effectively an extreme snakebite.

 

[CanucksTraveller]

How long since the tyre was last off / tube was fitted?
When you inflated it yesterday, was the tyre completely flat to start with? Depending on the answers I suspect it could be that the tube got pinched against the rim during inflation.

 

[Dwn]

How long since the tyre was last off / tube was fitted?
When you inflated it yesterday, was the tyre completely flat to start with? Depending on the answers I suspect it could be that the tube got pinched against the rim during inflation.

Inflation yesterday was just a top up; the tube has been on for weeks and I’ve previously cycled on it. Happened today at the 4 mile mark.

 

[Dwn]

That doesn't look like the rim was unseated by the inner tube deflating, rather the reverse. A gash like that is caused by the tyre coming off the rim and the inner tube being caught between them. Effectively an extreme snakebite.

That’s interesting. At the risk of seeming very stupid, what could have caused the tyre to come off the rim?

 

[ColinJ]

It looks like it might be on one of the seams on the tube. Tubes do sometimes fail that way when badly-joined seams come apart - a mate of mine bought a box of 10 tubes and every one of them failed like that; in his case, clearly a bad batch.

 

[ianrauk]

Looks to me as if the inner tube got stuck between rim and tyre

 

[CanucksTraveller]

Inflation yesterday was just a top up; the tube has been on for weeks and I’ve previously cycled on it. Happened today at the 4 mile mark.

Thanks... in that case I'd say the next most plausible reason is just that it was a tube that was faulty. Sometimes a minor fault in the seam will hold for a time, but eventually fail spectacularly. Not really common, but it happens.

At the risk of seeming very stupid, what could have caused the tyre to come off the rim?

Incorrect tyre size for one, but in your case I think that's not as likely.

 

[si_c]

It looks like it might be on one of the seams on the tube. Tubes do sometimes fail that way when badly-joined seams come apart - a mate of mine bought a box of 10 tubes and every one of them failed like that; in his case, clearly a bad batch.

I don't think it's that - if you look at the photo you can clearly see the line of the join tending away from the tear on the right hand side, and if you look at the top of the gash there is an odd shape which I would suspect is the origin point. The most likely explanation is that the tyre was improperly seated on the rim and when the two parted ways the tube was caught between and rapidly deflated causing the gash along it's length.

 

[ColinJ]

I don't think it's that - if you look at the photo you can clearly see the line of the join tending away from the tear on the right hand side, and if you look at the top of the gash there is an odd shape which I would suspect is the origin point. The most likely explanation is that the tyre was improperly seated on the rim and when the two parted ways the tube was caught between and rapidly deflated causing the gash along it's length.

You are probably right.

I think the thing to learn from this is to be extra careful not to trap tubes when fitting them. I made that mistake on my mountain bike once and didn't notice until mid-ride when I heard a strange rubbing sound. I stopped to investigate and saw a bubble of tube poking out from under the tyre. I watched in horrified fascination as it rapidly got bigger, and then suddenly... KERBANGGGGGG!!!!!!!!!!!!

As a novice, I also repeatedly damaged tubes when fitting them. I was carelessly using tyre levers to get the tyres back on, and pinching the tubes with the ends of the levers. These days I inflate tubes slightly before refitting tyres to reduce the chances of that happening. I try to minimise or avoid the use of levers. I can get certain types of tyre on and off with my bare hands, but need help with some some stubborn ones.

 

[Dwn]

This is a slightly better photo. When I stretch the tube slightly you can see a pretty big hole just beside the gash

 

[Dwn]

The idea that the tyre wasn’t seated properly makes perfect sense, but I’d been out on the bike a few times before this happened. Could the tyre bead have been working its way out over that period?

I certainly rode home in a very tentative manner with the new tube, in case I had missed something about the tyre of the rim, but close inspection shows that they look fine.

 

[si_c]

As a novice, I also repeatedly damaged tubes when fitting them. I was carelessly using tyre levers to get the tyres back on, and pinching the tubes with the ends of the levers. These days I inflate tubes slightly before refitting tyres to reduce the chances of that happening. I try to minimise or avoid the use of levers. I can get certain types of tyre on and off with my bare hands, but need help with some some stubborn ones.

I've done this sadly far too often. Now I don't use levers to get the tyres back on at all if I can help it, and I always inflate a small amount and then work the bead on both sides all the way around the tyre to ensure nothing is trapped. And as I inflate the tube properly I take care to ensure that the bead seats properly all the way around.

 

[mjr]

I've done this sadly far too often. Now I don't use levers to get the tyres back on at all if I can help it, and I always inflate a small amount and then work the bead on both sides all the way around the tyre to ensure nothing is trapped. And as I inflate the tube properly I take care to ensure that the bead seats properly all the way around.

I still use levers to refit, but take care not to stab the tube with them and check all the way round after refitting before inflation that I can see rim well underneath and not pinched tube. After you detonate one inside the shed with a track pump, you don't want that echo and ringing ears again!

 

[si_c]

I still use levers to refit, but take care not to stab the tube with them and check all the way round after refitting before inflation that I can see rim well underneath and not pinched tube. After you detonate one inside the shed with a track pump, you don't want that echo and ringing ears again!

In my case detonating one in the kitchen resulted in a positive impetus towards never doing that again in the form of a very angry wife with ringing ears whose misfortune was clearly caused by her making dinner at the time not my lack of attention to what I was doing.