What could have caused this puncture!

[Fields Electric]

Had this happen to me recently on an old 26" 1/4 rim. Yes the tyre was the correct size as was the rim. It was a modern tyre, the rim probably dates from the 1970's. I put it down to progressing technology. in those days I never used a track pump or knew of anyone that used one to inflate a tyre so it would never get to anything like the pressure stated on the modern tyre. Instead I only ever inflate it to 60 PSI i have never had an issue since. As for fitting tyres, I always put a little bit of air in the tube before using levers to put the tyre on. That way the tube is less inclinded to get trapped under the tyre bead.

 

[Big John]

Check the tyre for sharps. No sharps? Fit a new tube. Sometimes it's better not to question why. S##t happens ☹️

 

[Deleted member 1258]

Check the tyre for sharps. No sharps? Fit a new tube. Sometimes it's better not to question why. S##t happens ☹

I would also check that there's not a split in the tyre wall, I've never seen an inner tube damaged like that

 

[Dwn]

I’ve checked the tyre pretty carefully and can’t see any sign of sharps or damage. So far, the tyre not being seated correctly seems like the most likely of the explanations I’ve seen.

As an aside I thought I would double check that I hadn’t overinflated the tube, by using a different track pump. This one has a screw fitting rather than a lever arrangement. Unscrewed the pump after inflation and the valve core came out. Not having much luck with inner tubes today.

 

[andrew_s]

This happens when the tube is trapped between the bead and the rim when the tyre is fitted.

Normal instructions are to put a few pumpfuls of air in the tyre, then go round the wheel on both sides, pushing the tyre away from the rim flange to check for trapped sections of tube, but the check is frequently skipped even by those who are aware of the need (like me).{
(step 8.8 in the Park instructions)

The tyre normally presses against the rim flange tightly enough to keep any air getting into the trapped section, but cornering forces can move the tyre enough to allow a bit of seepage, and once enough air is in the trapped section, the intermittent seep becomes a rush, and the trapped section pushes the tyre away from the rim and the tube explodes through the gap.
It can take quite a lot of miles for there to be enough seepage to get to the runaway bubble stage. Sometimes the pushed back section of tyre remains inside the rim flanges giving the impression the tyre has burst inside the tyre, sometimes it ends up outside the flange, giving the impression the tyre wasn't mounted properly.

If the trapped section is large, the lift away and burst will happen towards the end of the initial pumping up.

 

[HobbesOnTour]

I’ve checked the tyre pretty carefully and can’t see any sign of sharps or damage.

Just on this, running a bit of cotton wool along the tyre can be a big help in finding sharp thingys. Depending on the tyre they can be surprisingly well hidden. And sharp! So watch fingers!

If that was my bike I'd be checking the other tyre (& wife's bike). A front wheel blow out may not be fun.

It does look like a pinched tube, but no harm to pump up just the tube(s) and check the seams.

 

[Dwn]

Good advice @andrew_s and @HobbesOnTour - I will check all tyres again. Looking back on strava I had a puncture on that very tyre 3 weeks ago (a bit of glass). I put a new inner tube in, and it’s looking quite plausible that I didn’t seat it as well as I thought that I had. It’s certainly left me feeling slightly wary about all the bikes (although the others have gone months without the tubes being changed).

 

[rogerzilla]

How much pressure? A Schwalbe Durano will blow off the rim at a mere 115psi. I have done it.

 

[Dwn]

How much pressure? A Schwalbe Durano will blow off the rim at a mere 115psi. I have done it.

It’s a Continental GP5000 with a maximum tyre pressure of 115. If my track pump was correct, I had it inflated to about 90. I’m planning to double check the pressure gauge on the pump, in case it is wildly out.

 

[Fields Electric]

Taken vintage bike out again today. Pumped up tyre using track pump after owner complained about soft tyre. I know the pump gage under reads by 15% so set it at about 70 psi. Guess what, tyre started to lift off the rim again. This time I caught it in time. It’s a steel rim with a schwalbe 26 1 1/4 tyre. I guess that there is an issue with the rim. As the front tyre same size steel rim does not have this issue.

 

[Twilkes]

Maybe not related but after inflating a patched tube to make sure the patch held, I noticed bulging either side of the valve and at about 2 o'clock on the image below.

Is that normal? I'm guessing that if it's inside a tyre it would be limited in how much those sections could expand, but could it indicate a weakness in the rubber?

 

[Dwn]

Maybe not related but after inflating a patched tube to make sure the patch held, I noticed bulging either side of the valve and at about 2 o'clock on the image below.

Is that normal? I'm guessing that if it's inside a tyre it would be limited in how much those sections could expand, but could it indicate a weakness in the rubber?

View attachment 582530

I’ve seen that before with other inner tubes - didn’t seems to make much difference when fitted within the tyre.

 

[andrew_s]

The bulges are restricted in size by the tyre, and not a problem in normal use. They are because the thickness of the rubber in the tube isn't even.

They do cause difficulties when trying to find the location of a small & slow puncture - normally you could just inflate the tube (outside the tyre) until it's big enough that the leak is fast enough to be findable, but if you tried that with a bulgy tube, the bulges would burst before the non-bulgy bits got big enough that any small hole would leak quickly.

 

[bikingdad90]

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!

I’ve done that but worse still I was crouched next to the tyre going round it to make sure everything was ok when it blew! Never have I jumped so much. My tactic now to ensure the tyre is seated after fitting a new tube is to pump up to the max PSI and then fully deflate before inflating to my normal PSI of about 90 for 25x700.

 

[Tom B]

I had a similar blow out on a 26" tyre which was slightly over pressure. The tyre was old and possibly not seated 100% on the bead.

I got about 500yrds down the road and stopped to speak to a chap on the pavement. I was stopped with some weight on the saddle and felt the bike rise slightly as the tyre came over the rim the innertube popped out, ballooned and exploded along a seam.