A strange flat.

[Tenpoints]

Pre-race warmup this morning cruising Majura trails, rear wheel goes psshhiiw! Lucky we're not racing yet. I carried it back to the start (through the bush). Upon inspection of the damage I found that the valve was not in its normal place sticking through the rim hole, it was in fact 180 degrees around the wheel squashed against the rim and the tube!


Later went on to pinch my spare within 15 minutes of starting lap 1, so it was all in all a pretty fail morning.

Anyway, tube was a Specialized turbo tube and tyre is a Specialized Renegade 29*1.95".
I guess pre-talced tubes have a weakness.
Tyre was at 38psi.
The little nut that is supposed to hold the tube in place was absent in this situation, mainly due to the threaded part of the valve being out of reach even when pumped up.

It's a moot point now as I'm going tubeless but I just wonder how common this kinda thing is and what the main catalysts are?

 

[pistonbroke]

So what caused the flat? Where was the hole?

After my third flat in a week, I found my rim tape had shifted, exposing the spoke holes to the tube. The edges of the spoke holes were enough to wear hole on the inside of the tube. This had caused 2 out of the 3 flats. The other was caused by something going through the tyre.

 

[Tenpoints]

The hole is about 90 degrees around from the valve, on the inside (facing the rim). It's a blowout style hole and I presume it was caused when the valve slipped inside. I'm not surprised that it flatted under those circumstances, I'm just perplexed as to how it managed to spin so far around the tyre.

 

[quiggs]

I find the tube if it doesn't have the lock nut holding the tube in place can cause the tyre tube to shift/move around the rim, generally against the braking force and only on the front and it only happens on my commuter! Occasionally I have forget to check it and has ripped the valve stem from the tube. Not sure why it happens other than is it the tyre bead moving against the rim with braking forces?? Dunno.

Doesn't solve why but at least your not the only that it has happened to.
quiggs

 

[.stu.]

I find tubes work best when folded up in my toolpouch, that way they don't interfere with the tubeless tyres, stans goop and rimtape. They never seem to exhibit these problems you describe when used in this way.

 

[bunchie34]

i find tubes work best when folded up in my toolpouch, that way they don't interfere with the tubeless tyres, stans goop and rimtape. They never seem to exhibit these problems you describe when used in this way.

^this. Hard.

 

[Tenpoints]

Furthermore (although not necessarily related) upon attempting to seal my DT Swiss X450SL rim and "2bliss" Fastrack tyre in a tubeless configuration, I discovered that despite liberal amounts of True Blue Goo (water based stan's alternative", it would not stop leaking through the weld opposite the valve hole. Yes the rims are pre-equipped with blue specialized tubeless tape. Manufacturing defect? Was told the rims were tubeless, although more of a verbal offhand remark than written spec. Will take it to LBS tomorrow to try and get it sorted.

 

[bunchie34]

Furthermore (although not necessarily related) upon attempting to seal my DT Swiss X450SL rim and "2bliss" Fastrack tyre in a tubeless configuration, I discovered that despite liberal amounts of True Blue Goo (water based stan's alternative", it would not stop leaking through the weld opposite the valve hole. Yes the rims are pre-equipped with blue specialized tubeless tape. Manufacturing defect? Was told the rims were tubeless, although more of a verbal offhand remark than written spec. Will take it to LBS tomorrow to try and get it sorted.

I sealed the same rim & tyre combo with DT Swiss tubeless kit up just fine with Stans sealant.

Rims, generally, are not actually tubeless unless they're marked UST. Hence the need to run tubeless rim tapes (not standard rim tape) and/or the full Stans rubber strip kit or similar. Surprised you're having a leak at the weld...Have you tried ripping off and retaping the rim first?

 

[akashra]

I've seen the same thing happen on a few tubes where the nut was not used. Some people think they're being smart of weight conscious by not using them. I fail to see the point at the cost, example being the experience you've just described.

 

[Tenpoints]

Surprised you're having a leak at the weld...Have you tried ripping off and retaping the rim first?

Haven't tried that, but I had a shocker this arvo trying to get ANY setup to work, including two different tyres (the Renegade had a cut in the sidewall), my I9 wheel (worked until the valve blew out through the hole!) and various other valves. I think by the fifth(!) attempt there wasn't enough sealant left to plug the main air gap which was between the valve and the rim.

I've seen the same thing happen on a few tubes where the nut was not used. Some people think they're being smart of weight conscious by not using them. I fail to see the point at the cost, example being the experience you've just described.

The main rationality I've heard is it saves precious seconds when changing a tube in the race, since you don't need to spend time unthreading (and rethreading). Personally I've never really bothered with that, as most of my time is spent fatiguing my arms with a tiny little pump.

 

[quiggs]

I've seen the same thing happen on a few tubes where the nut was not used. Some people think they're being smart of weight conscious by not using them. I fail to see the point at the cost, example being the experience you've just described.

Don't know about the weight component, they are just a pain in the arse when it comes to changing tubes having to remove them before putting the valve through the rim hole and then putting it back on again afterwards, but not too tight because then the tyre bead can get caught outside the tube when inflating.

 

[Pebble]

Funny I had a similar thing happen to me just recently, was riding my bmx, got about 2.5km down the road and then all of a sudden the back tyre goes pssst and completely flat (and I was on bitumen at that stage).
Had to get to town so dumped the bike in the bush, on later inspection at home found this....



I'm thinking I mustn't have paid enough attention to making sure the tube / valve was square with the rim when mounting the tyre! Never had such a thing happen on a mtb with either presta or schrader valves. But my prestas always did have the little things screwed on them, makes it easier to pump up a flat that way anyway.

 

[Stevob]

Under enough force, the tyre can slip on the bead, pulling the tube around with it. This is particularly a problem when the tyre has been removed and refitted a number of times, and the culprit is usually that the tyre bead/rim contact isn't entirely clean. I've had valves rip away from the tube (and I always use the nuts Tim) because of tyres sliding around the rim, usually on low pressures, but not always.

Funny that I haven't had this problem since going tubeless, where clean contacts are essential for sealing properly.

As for sealant leaking through the rim joint, just sounds like the tape wasn't applied properly. Also tubeless valves which aren't tightened properly can allow sealant, or just leak air, through to the cavity below the tape, where it can escape through the spoke holes.