What would cause an inner tube to spontaneously explode?

Trapped between the rim and the tyre? 

Split in the tyre?

Even a smallish one can cause the tube to bulge out, which can then explode quite impressively (even some time later when you're not on the bike). I speak from experience. Did your colleague need new trousers?

Split in the tyre?

That would be my guess. Otherwise a tyre that has been overinflated and stretched the bead or has been fitted incorrectly and the bead wasn't seated properly.

Split or bead not seated. Either of those will cause the innertube to bulge and fail quite quickly with a proper bang. Wheel might need retruing too.

Causes of this that have happened to me.

Splits in tyre wall this can occur when you are not riding, we had a rear tyre explode while we were having tea and cake in a cafe in Exmooor , Not seating the tyre properly and pumping it up, most effective in a cellar for a loud bang and splits in the rim due to brake wear.

Have you at any point in the last week or so said words to the effect of "It's been ages since I last had a puncture"?

Trapped between the rim and the tyre?

I've had this and it had been on the bike for months before it went.

Rim tape not centred causing inner tube to rub on rough edge of spoke hole?  Been there, done that.

Better when it's the front tyre of your road bike which is just behind your head in the car.......

The only time it happen to me I was upstairs and my bike was in the kitchen ready for an early morning ride the next day. Load bang and a completely deflated tyre.

When I investigated the culprit was worn rim tape that had finally given out over a spoke hole which then punctured the tube. Appreciate this is slightly different and I presume you have ridden your bike today but maybe it shifted or something during the ride?

I had a tubeless one explode a few years ago. It was worn, shall we say, to the point where it rolled nearly as fast as a slick but I was too lazy to change it. At the end of my usual training ride, there's a flight of stairs back down to the road, so I hammered down that and then rode home, which was about 20 minutes. When I got home, I noticed the tyre had a blister in the middle of where the tread used to be so I guessed that smacking down the stairs had caused it to start to delaminate and air was leaking out and getting trapped under the tread. I parked the bike on the balcony and sat down for a coffee when it went off with an enormous bang about three feet from me. It had delaminated about a quarter of the way around the tyre and then the tread had popped like a balloon.

We had an inner tube on our buggy explode shortly after arriving at a resort in Menorca. Alway assumed it was a combination of weakening caused by heat and the air inside the tube expanding because, it was  close to 40 degrees in the shade and the wheel was facing the midday sun.

Do you work somewhere very hot and sunny?

If the tyre is a bit baggy, the tube can fail where it joins the valve. Had it happen a few times on my old Kona with Panaracer tyres.

I think the tyre would rotate on the rim, stressing/cutting the tube and it giving up when warm in the house.

Did the tube explode, or did the tire blow off the rim (and then the tube exploded)?

Another possibility is that you had a 'pinch flat' that didn't quite go through the tube completely, but weakened it.  Eventually the weakened bit can't hold on any longer.

I parked the bike on the balcony and sat down for a coffee when it went off with an enormous bang about three feet from me.

I remember being stood outside the pub after a Peaks Pootle ride when the inner tube on someones parked bike suddenly exploded right next to us. It scared the living bejesus out of all of us.! It didn't half go with a bang!

No idea what caused it.

Heat. Having watched a few go off at a Reading Velodrome open meet on a nice sunny day, when bikes with tyres at 140+ PSI are left in the sun for too long. Was the bike near a radiator?

Otherwise trapped inner tube has seen off a few latex tubes in my time (user error), but typically only hone just getting rolling.

What would cause an inner tube to spontaneously explode?

Dynamite? Yes definitely dynamite would do this…. Or what Aidy said 👆🏻

They’re the only reasons I can think of.

Great replies everyone, thanks.

I've had a chance to hace a look now. The edges of the tyre are a little raggedy and a few threads have come loose, so I reckon the tube managed to squeeze through a gap as some have suggested. Could be the rim tape, I'll have a good look.

Did your colleague need new trousers?
I think he experienced great schadenfreude from the episode. I don't really think it was sabotage, but if I did this character - a good friend - would be my prime suspect. He di say he jumped quite high.

Have you at any point in the last week or so said words to the effect of “It’s been ages since I last had a puncture”?
I would NEVER tempt fate like that. I changed the tube at the weekend as the old tube was losing air (though mysteriously I cannot find a hole anywhere, and it has stayed up just fine in my garage), so it must have been then that whatever caused it occurred - though I've done a good 40km on it since then.

I fancy some new tyres anyway. Anybody tried Vittoria Terreno Dry?

I changed the tube at the weekend

My guess is that the new tube got pinched somewhere under the tyre as you installed it. Pump it up and the trapped bit is pressed against the tyre bead, the rim or whatever and it'll hold for a bit then just explode.

Weirdest one I had was a tyre exploded while I was riding on rollers. Turned out that the tyre had a tiny hole in the sidewall, the tube bulging through it caught on the brake blocks and after half a dozen revolutions of the wheel, the whole thing exploded very loudly. And then I fell off the rollers.

I’ve seen inner tubes freeze with over zealous CO2 input, they then become brittle and subsequently fail. Normally fairly quickly though.

Now I’m at home I’ve removed the wheel and can see that the issue is rim tape. There’s a small fold that leaves a space big enough for a tube to squeeze into.

So tomorrow I’m off to buy tape. I’ve never fitted tape before so it’s going to involve lots of guessing. Lots of cleaning before sticking I imagine. I have WTB i19 rims, so I’m guessing that I’ll need fairly narrow tape. Are they all much of a muchness?

Do it inside where everything is a bit warmer. 2-3mm wider tape than the internal diameter of the rim. Opinion varies as to whether you start at the valve side or opposite. My pre taped DT Swiss wheels have always had the tape overlap at the valve hole. About 3-4 inches either side of the valve so 6-8 inches overlap. Super clean the rim bed with IPA, have the wheel out in front of you and get someone to hold it if poss while you use two hands to apply each section before moving the wheel round a bit. Plenty of tension on the tape and sort of wiggle it side to side as you apply it while pressing down firmly with a microfibre to smooth out any air pockets. Go slowly. Cut at 45 degrees optional. Have the overlap in the opposite direction to the rotation direction so the sealant slopping around inside is washing over the overlap rather than trying to get under it - wind the tape on anti clockwise when looking at it from the drive side.

I run them on my gravel bike.  Good tyres. I like them!

I think he experienced great schadenfreude from the episode.

In what way?

I don't think it's been said yet, but my guess would be some sort of demonic possession or other supernatural involvement. This is a classic example of how we fail to accept that we do not understand everything in our world, hence people inventing UFOs to explain stuff. I guess it coul be down to UFOs though?

it happens, less common now ppl use tubeless, and is another great reason to do away with tubes.. had mine explode after repairing a puncture, was turned doing something else, and it went quite unexpectedly  (might have caused a brown pant moment).

Ok, rim tape re-glued, new tyre and tube in place (700 x 40 on the fron, 700 x 38 on the back - will I die?), not pumped up too hard - let’s see what happens.

I had one go because the rim braking surface was completely worn out to the point it split and the tube forced its way out. Scared the crap out of me, the bike was parked in my hallway and it was 3am.

It’s cracking when they go bang in the hallway, I never realised what was meant by your ears ringing till I experienced it.

One of my tubeless went thru a phase of going slowly down then popping off the bead in the early hours of the morning with a nice ‘crack’ which made the dog jump a mile.

(700 x 40 on the fron, 700 x 38 on the back – will I die?)

yep(eventually),as long as the tyre markings align with the valves you’ll be fine 🙂

as long as the tyre markings align with the valves you’ll be fine

Of course! What sort of monster do you take me for?

Better when it’s the front tyre of your road bike which is just behind your head in the car…….

Try a road one at 90 psi going at 3am when you store the bike in your bedroom.

The other thing to look out for is making sure the correct size tube is in. So a 1.5-2.1 inner tube in a 2.5 width tyre is stretched and on a hot day, they can split.