Inflating Presta threaded valve tubes - a tip.

[rrarider]

How did the presence of the finger tight lockring cause the damage (or increase the risk of damage) please?

With a flat tube, part of the the rubber shoulder is pulled into the rim hole. Even with good quality Velox rim tape, inflating the tube to maximum pressure for the tyre (115 psi) then causes a tear in the shoulder area of the tube.

 

[mjr]

Stores momentum to help me up the hills.

It's also used to balance the wheel, as the valve weight plus collar minus hole is closer to the weight of the strengthener across the rim joint opposite. Spin the wheel and if it stops valve down every time, remove the collar, but if it stops valve up every time, add collars until you balance the strengthener.

 

[rrarider]

Here's a photo of the tear in one of the tubes, which can only be seen when it's held open, in this case by a clamp and a book :

 

[Pat "5mph"]

Not sure about this warning: I like the lock rings, like @glasgowcyclist said they help keep the valve out of the rim for easier grip for the pump.
They also reduce the chance of ripping the valve out while using a mini pump without hose, imo.
Like @I like Skol, I think the reason for the explosions is elsewhere.

 

[I like Skol]

Those valves don't look like presta valves i am used to. There is normally a much more robust ring of reinforcement where the valve is mounted. I have to ask, is the rim drilled for Schrader?

My guess is borderline weak tubes coupled with a Schrader rim and a coincidental simultaneous failure of two shoddy tubes.

 

[Alan O]

This is something I'd never heard of before, but then I don't fasten the lock nut until I've fully inflated the tyre, so I've never come across the problem of potentially exploding tyres - by luck rather than judgment.

Then this morning I was swapping tyres and I paid particular attention to not fastening the lock nut until after full inflation. I got the two tyres on, then a few minutes later with the bike just standing there... Bang! Rear tube exploded and threw the tyre off. And the cat, which had been sitting next to the wheel, has never moved faster in its life.

There was a six-inch tear in the tube with a small portion completely blown off. And you know what? It was nowhere near the valve and nothing to do with the lock nut - but don't you just hate the way the coincidence fairy works at times like this?

 

[Tim Hall]

This is something I'd never heard of before, but then I don't fasten the lock nut until I've fully inflated the tyre, so I've never come across the problem of potentially exploding tyres - by luck rather than judgment.

Then this morning I was swapping tyres and I paid particular attention to not fastening the lock nut until after full inflation. I got the two tyres on, then a few minutes later with the bike just standing there... Bang! Rear tube exploded and threw the tyre off.

No. The tyre wasn't fitted properly, was unseated by the tube which, unconstrained by the tyre, then exploded.

 

[Alan O]

No. The tyre wasn't fitted properly, was unseated by the tube which, unconstrained by the tyre, then exploded.

Ah yes, that makes sense.

 

[Ajax Bay]

With a flat tube, part of the the rubber shoulder is pulled into the rim hole. Even with good quality Velox rim tape, inflating the tube to maximum pressure for the tyre (115 psi) then causes a tear in the shoulder area of the tube.

Whilst this could be 'head of the pin dancing' I wonder how much force the lockring exerts on the inner tube compared to the surely much, much greater force which is exerted by the air pressure once the tube is inflated.

My guess is borderline weak tubes coupled with a Schrader rim

OP - what is the diameter of the drilled valve hole in the rim? (to the nearest 0.3mm please)
Personally I slip a 'polo mint' shaped piece of rubber over the valve a new inner tube before using it (or refolding it for carriage as a spare). This protects the base of the tube (where the OP had their failures).
(Note: max 12mm diameter and cut a 5mm 'cross' in the centre to push the valve through - rubber from a discarded inner tube)

 

[mjr]

Valve condoms!

 

[rrarider]

I started this thread, merely as a piece of advice for anyone using Vittoria tubes who was thinking of tightening the lock collar whilst the tube was flat. Readers can take it or leave it; I don't care one way or the other. I know what caused the rip in the tubes. I hadn't much intended to start a Q&A session.

OP - what is the diameter of the drilled valve hole in the rim? (to the nearest 0.3mm please)

No matter which rims I was using, I doubt that I would make the effort to unmount the wheel, tyre and tube to measure the hole with my Vernier caliper in order to satisfy your curiosity. As the rims are Mavic MA40s, which have a well deserved reputation for being monstrously hard to refit tyres on, my reluctance to do so is even stronger.
To the best of my knowledge, Mavic only made this rim with a Presta fitting; there would be no point in making such a narrow, light rim to take a Schrader valve. Looking at the assembled wheel, the hole is just about wide enough to take a Presta valve stem and no more.

 

[youngoldbloke]

OP - either it's the tubes or the new chuck. If you haven't had the problem before, and you followed the same procedure in the past then maybe it's the use of the new chuck. In my experience, when fitting a new tube (if using a lockring with a threaded valve, which I try to avoid using), as the tube is inflated the valve stem is pushed out from the rim, requiring further tightening of the lock ring. Easy answer to your problem - don't use lock rings. You can push the valve with your thumb on the tyre to enable you to push on a chuck when inflating from flat.

 

[User6179]

No matter which rims I was using, I doubt that I would make the effort to unmount the wheel, tyre and tube to measure the hole with my Vernier caliper in order to satisfy your curiosity.

Listen mate, this is Cycle Chat, get the Vernier caliper out and get the hole measured and less of the attitude, you have 5 minutes!!

 

[Ajax Bay]

I started this thread, merely as a piece of advice for anyone using Vittoria tubes who was thinking of tightening the lock collar whilst the tube was flat. Readers can take it or leave it; I don't care one way or the other. I know what caused the rip in the tubes. I hadn't much intended to start a Q&A session.

Piece of advice much appreciated but

Listen mate, this is Cycle Chat,

Don't you think that your experience, which is unusual, begs the question "why?"?
I can't see how a tiny bit of force exerted by the lockring is going to tip the balance of the force on the inner tube valve base area once the tube is inflated. You "know" what caused the rip. I'm interested in why it was caused. Why would Vittoria tubes be particularly vulnerable to this failure?

 

[mjr]

[QUOTE 5289587, member: 45"]I'd suggest that the most common cause of tube failure at the base of the valve is movement of the valve by the pumping action of inflating the tyre.[/QUOTE]
Only if you're daft enough to use pumps with no hoses.