From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Presta valve separating from tube
Date: 4 Oct 2000 22:53:48 GMT

Bob Comiskey writes:

> The valve separated from the tube as I removed the pump chuck. Second
> time in a couple of weeks, third time recently. The tubes were all
> Specialized 700x20-28, labeled "thin" on the tube itself.

Don't let anyone tell you it's user error.  These are faulty tubes and
should be returned to the shop they came from.  How else are we going
to let the MFG know that the product is faulty.  This happens much too
often to be ignored.  Classically the brass stem comes out of the
reinforcement pad on the tube with a slight coating of rubber, but
sometimes even clean.  This is a production control problem that can
be fixed, but only if there is some feedback from users.

I carry an old screw-in type stem from tubulars in my patch kit that
enables me to continue to use the tube when this happens on the road.
Latex tubular tubes all had screwed on stems because you can't
vulcanize metal to latex rubber.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Presta Valve ripping out of tube.  Replacement valve available?
Date: 9 Aug 2000 20:20:12 GMT

Stewart Ferguson writes:

>> That might coincidentally occur with tire slip, something unheard of
>> on road bicycles with around 100psi inflation where tubes fail as
>> often as elsewhere.  I don't think you have cause and effect coupled
>> in your experience.  How else do you propose that road tires with high
>> inflation pressure, that do not move, experience this failure?

> As I stated.  This is OFTEN caused by tyre slip.  It is a gradual
> effect that will be noticed over a period of time.  If you think
> that your high pressure tyres do not move gradually on the rim then
> please let me know what tyres you use.

I have not had rotational motion between tire and rim on any road tire
that I have used, and I have ridden many until the tread was gone.
That tires "move" on rims is evident from wear marks on the bead
chafing strip that imprints its image on aluminum rims, but this will
not affect the position of the stem with respect to the stem hole in
the rim.  Your "gradually" dodge does not make your contention valid.

> As Bob stated in his first post his problem can be caused by using
> certain pumps or as you state poor quality tubes.  I was only giving
> another explaination.  This problem is more prevelant with kids
> bikes or poorly maintained adult bikes where tyre pressure has not
> been maintained at the correct level.

Stop squirming.  These are faulty tubes whose stems are improperly
attached.  I don't understand what interest there is in throwing this
failure at the feet of the user.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: Presta Valve ripping out of tube.  Replacement valve available?
Date: 12 Aug 2000 00:38:34 GMT

Stewart Ferguson writes:

> I do not know if this is worth it, you are obviuosly one of these
> people who has one opinion. Its yours and its right. But here goes
> anyway. Oh by the way I will not be posting a respones to you next
> inevitable rant.

Please, not so petulant.  If you want to make technical claims than
you better have some evidence to support your claims and then
participate in the discourse.

>> I have not had rotational motion between tire and rim on any road
>> tire that I have used, and I have ridden many until the tread was
>> gone.

> Good for you.

That doesn't address the question, which is that over long periods of
use no circumferential motion takes place on a conventional road tire
with normal inflation.  "Good for you" is not part of this discussion.

>> That tires "move" on rims is evident from wear marks on the bead
>> chafing strip that imprints its image on aluminum rims, but this
>> will not affect the position of the stem with respect to the stem
>> hole in the rim.

> So let me get this straight. You are now saying that if the tyre
> does move (contrary to what you said earlier).  Then this will not
> effect the position of the stem.  I may be mistaken here but I have
> often change tyres with tubes stuck to the inside of the tyre.  You
> say that this will not effect the position of the valve stem.  Hmm,
> interesting.

Wear occurs from rotational motion of the tire bead when the casing
ovalizes as the tire bears against the road.  If you inspect the bead,
you'll notice that there is a special cloth strip expressly for this
purpose and that it is not structurally connected to the casing
plies.  This fretting motion has nothing to do with circumferential
movement and the textured wear marks that it causes in the aluminum
rim verify that it does its motion in place.

>> Your "gradually" dodge does not make your contention valid.

> I do not know what I am trying to dodge!!

That a road tire does not creep, gradually or at all.  Don't be coy.
You needn't take the readers of this newsgroup to be unaware of these
ploys.

>> Stop squirming.  These are faulty tubes whose stems are improperly
>> attached.  I don't understand what interest there is in throwing this
>> failure at the feet of the user.

> Squirm, why would I be squirming.  Unless I am mistaken or you are
> telepathic, Bob did not state the quality of tube he was having a
> problem with.  I did agree that it could be faulty or badly made
> tubes.

That there are many tubes being sold with faulty stem adhesion has
been established by many occurrences of separations with none of the
supposed reasons you have presented.  No tube shifting, inflation with
too much heat from a frame pump, overtightening the jam nut, or
running at low inflation.  The opposite, that is that a tube without
this flaw cannot be made to release its stem by pulling off an
inflation chuck or frame pump, or by running it with a canted stem,
can be demonstrated.

> As I said before (and I will say it again for your benefit).
> Now read carefully.

> I was only giving another explaination.

And I ask, why do you make the effort to lay this at the feet of the
user when it is fairly well established that these are faulty tubes.
The remote possibility that the user caused this by faulty use is
presumptuous in light of other people's experience.

Jobst Brandt      <jbrandt@hpl.hp.com>

From: jbrandt@hpl.hp.com (Jobst Brandt)
Newsgroups: rec.bicycles.tech
Subject: Re: inner tube valve blowing
Date: 26 Jun 2001 00:11:42 GMT

Kevin Griffin writes:

> I am getting tired of my inner tubes blowing at the seal at the base
> of the valve.  Are all inner tubes this unreliable?  Or perhaps I
> should be deflating my tires (at least partially) between rides?
> sounds like a pain in the ass.

There have been many such tubes whose stems separate for no valid
reason although many people always look for the cause where it
isn't... the user.  One thing that you can do if you have access to
old tubulars or a bike shop that throws out tubulars with latex tubes.
Latex tubes have separable valve stems that can be removed by
loosening the jam nut.  The stem then fits perfectly in the round hole
where the stem separated from the butyl tube.  Spit on the mushroom of
the tubular stem, pop it in the hole and snug up the jam nut and you
have a new tube.  When you throw the tube away, save that stem and
always carry one of these stems in your patch kit.  I've done it often.

Jobst Brandt    <jbrandt@hpl.hp.com>