Our shop used to stock the lighter of Tni's TPU tubes,
the "LIGHT 24" with a nominal weight of 24g (as opposed to the 35g version)
(past tense).
↑Both of these tubes—I didn't just sell them,
I installed them on tires myself—already have holes and have punctured.
The one in the upper image had only been used for about 3 days,
and the lower one went completely flat
a few hours after inflation,
puncturing without ever having been ridden.
Let me pump it up.
This valve is plastic, which is
part of the reason the entire tube is so light,
but French valves are normally sized at 6mm,
with the valve being undersized and the rim hole oversized
(when the tolerance difference is large,
it causes the valve rattle problem),
whereas brass valves typically measure around 5.9mm in diameter,
this valve is about 6.0mm,
and moreover, the section of the valve body just below the threads
expands from the threading process
and reaches about 6.2mm.
This not only won't fit through a Campagnolo valve bush,
it barely fits into the rim holes
of current Shimano carbon wheelsets.
The pump head on my floor pump also
can't pass this expanded section, so
I'm able to inflate it by having the pump head
squeeze the threaded section where the valve core cap attaches,
but I suspect there are some pumps (floor or portable)
that simply can't maintain an airtight seal against this valve.
I inflated the tube that had been used for 3 days.
Air keeps leaking out of the hole,
so I'm pumping as I take the photo.
There's a protrusion that's formed next to the valve hole, but
the tip of that protrusion is thinned and has a hole.
Inside the tire, the protrusion was folded over and
the hole was partially sealed, so
it became a slow leak that didn't lose air very quickly,
but as a standalone tube, air escapes immediately.
Now for the tube that punctured within a few hours—
it has a larger hole than the previous one
and can't maintain its inflated state with just pumping.
↑This is the puncture hole.
I sealed the hole with masking tape.
The failure pattern is the same.
Not as severe as the previous tube,
but protrusions are starting to form.
Two protrusions form on either side of the valve, fore and aft—
four in total—and when their tips become thinned,
holes form.
There's a clear, hard circular component directly below the valve,
and when the tube stretches, the difference between
what stretches and what doesn't stretch next to this component is large,
so protrusions develop.
↑This is a tube I took out of a tire during a separate wheel inspection
and photographed for the article.
It's a so-called Chinese TPU tube—not from a famous brand like Tubolito—but
it clearly shows
countermeasures taken with knowledge of protrusion formation.
The clear, hard component at the valve base is
thicker than Tni's version and extends further front-to-back,
and despite what must be considerable age and use,
no protrusions have formed.
↑Like this,
but since this tube is clearly thicker than Tni's LIGHT 24, it's possible
that's why the problem doesn't occur.
I've never stocked it, but the Tni LIGHT 35
might resist protrusion formation.
Even with the LIGHT 24, not all units puncture even if protrusions form,
but whether I installed them or customers did,
the failure rate(though I can't call it a defect rate for certain reasons)
is noticeably higher than other tubes,
so we've stopped selling the LIGHT 24 at our shop.
the "LIGHT 24" with a nominal weight of 24g (as opposed to the 35g version)
(past tense).
↑Both of these tubes—I didn't just sell them,
I installed them on tires myself—already have holes and have punctured.
The one in the upper image had only been used for about 3 days,
and the lower one went completely flat
a few hours after inflation,
puncturing without ever having been ridden.
Let me pump it up.
This valve is plastic, which is
part of the reason the entire tube is so light,
but French valves are normally sized at 6mm,
with the valve being undersized and the rim hole oversized
(when the tolerance difference is large,
it causes the valve rattle problem),
whereas brass valves typically measure around 5.9mm in diameter,
this valve is about 6.0mm,
and moreover, the section of the valve body just below the threads
expands from the threading process
and reaches about 6.2mm.
This not only won't fit through a Campagnolo valve bush,
it barely fits into the rim holes
of current Shimano carbon wheelsets.
The pump head on my floor pump also
can't pass this expanded section, so
I'm able to inflate it by having the pump head
squeeze the threaded section where the valve core cap attaches,
but I suspect there are some pumps (floor or portable)
that simply can't maintain an airtight seal against this valve.
I inflated the tube that had been used for 3 days.
Air keeps leaking out of the hole,
so I'm pumping as I take the photo.
There's a protrusion that's formed next to the valve hole, but
the tip of that protrusion is thinned and has a hole.
Inside the tire, the protrusion was folded over and
the hole was partially sealed, so
it became a slow leak that didn't lose air very quickly,
but as a standalone tube, air escapes immediately.
Now for the tube that punctured within a few hours—
it has a larger hole than the previous one
and can't maintain its inflated state with just pumping.
↑This is the puncture hole.
I sealed the hole with masking tape.
The failure pattern is the same.
Not as severe as the previous tube,
but protrusions are starting to form.
Two protrusions form on either side of the valve, fore and aft—
four in total—and when their tips become thinned,
holes form.
There's a clear, hard circular component directly below the valve,
and when the tube stretches, the difference between
what stretches and what doesn't stretch next to this component is large,
so protrusions develop.
↑This is a tube I took out of a tire during a separate wheel inspection
and photographed for the article.
It's a so-called Chinese TPU tube—not from a famous brand like Tubolito—but
it clearly shows
countermeasures taken with knowledge of protrusion formation.
The clear, hard component at the valve base is
thicker than Tni's version and extends further front-to-back,
and despite what must be considerable age and use,
no protrusions have formed.
↑Like this,
but since this tube is clearly thicker than Tni's LIGHT 24, it's possible
that's why the problem doesn't occur.
I've never stocked it, but the Tni LIGHT 35
might resist protrusion formation.
Even with the LIGHT 24, not all units puncture even if protrusions form,
but whether I installed them or customers did,
the failure rate
is noticeably higher than other tubes,
so we've stopped selling the LIGHT 24 at our shop.