Matt O'Toole said:Quoted message said:Quoted message said:> What difference does threaded/non- make?
Quoted message said:Quoted message said:Quoted message said:The non-threaded stems slip more easily out of my Silca pump's
chuck. This gives the two-fold advantage of not wearing out the
chuck's rubber grommet as quickly and vastly decreasing the
frequency with which I pull the valve stem loose from the tube
(it seems that this almost always the eventual cause of death
for my tubes with the threads).
# Subject: 8b.30 Valve stem separation flats
# From: Jobst Brandt <[email hidden]>
# Date: Mon, 16 June 2003 14:13:14 PDT
#
# A flat caused by valve stem separation, a manufacturing flaw, is
# less dangerous because it usually becomes apparent during inflation.
# If it occurs while riding, it causes a slow leak as the vulcanized
# brass stem gradually separates from the tube. When this occurs, the
# stem can be pulled out of the tube entirely to leave a small hole
# into which a valve stem from a latex tube of a tubular tire will
# fit. Stems from tubulars have a mushroom end, a clamp washer, and a
# locknut, that fit ideally into the hole left by stem separation.
# Such a used stem should be part of a tire patch kit. Any good
# bicycle shop that handles tubular tires or latex tubes should have
# used ones if they weren't thrown away.
#
# In a self accusative manner, riders often place blame for this
# failure on errant inflation, the use of the anchor nut on the stem,
# or some other feature of the rim that they failed to ameliorate. On
# close inspection, separated stems show that the rubber peeled away
# leaving only a slight black trace on the stem where the leak began.
# This isn't caused by any of the usually believed mechanisms. It is
# a manufacturing flaw.
#
# ------------------------------
Quoted message said:Quoted message said:Quoted message said:So, the question remains, who (besides Torelli) makes Presta tubes
with non-threaded valve stems?
Quoted message said:Quoted message said:I don't find any on the shelves of the bicycle shops I visit. I
would like to know what you find is the advantage of such a stem.
You can always leave the stem nut off id you like.
Quoted message said:I don't have problems with the threads on the shaft of the stem, but
the threads around the tip, that the cap screws onto. Depending on
the brand, these keep my pump from getting a good seal, making it
impossible to put more than 30-40 psi of air in the tire. I swapped
a tire the other day, and went through 3 tubes before I found one
with a valve stem that worked with my pump. I think the one that
worked was a Continental.
This sounds like a pump problem. These Presta stems with threads as
we commonly see them have been in use for a long time without problem.
When the new generation of riders came along without the ability to
operate the old Silca frame pumps, with which tubulars were inflated
daily, they and their Campagnolo pump chucks vanished. I have no
trouble inflating tires with these pumps and my floor pump has a Silca
chuck with a pressure relief button that works fine. In fact, the
smooth stems sometimes get ejected by inflation pressure.
Quoted message said:Stuff like this can be really frustrating, especially because
there's no excuse for it. Distributors must know their stuff
stinks, but sell it anyway -- like the Specialized MTB tubes that
the stems fell out of, which shops continued to sell for years, or
those [censored] plastic Mt. Zefal mini pumps.
It seems the separating stems were a general malaise for a while,
indicating that possibly the same company made all the different brand
packaged tubes. Now it seems to be thin sections at the tube splice.
Jobst Brandt
[email hidden]
