This is a continuation of my previous post.
So why is it so hard to pump air into this valve?
It's because the threads on the valve are only cut halfway around.
Specialized tubes—which aren't tubeless valves but regular tubes—use the same design.
I'd been planning to write about this eventually, so I had images in stock
(though the image above is actually from a Specialized tubeless valve).
I don't know if they think it looks cool or what,
but with these types of valves, the pump head's grip is abnormally weak,
causing air to leak around the head or—once pressure builds up—the head pops off with a bang.
French valves come both with and without threads cut into them.
But except in cases like tubeless valves where screwing the valve nut onto the rim is essential,
the valve nut isn't actually a functional component.
Since it's not functional, threadless valve designs exist.
When I measured the outer diameters of both types, they came out to just under 6mm.
The rim's valve hole has an inner diameter of just over 6mm.
I think tolerances are set so that nominally 6mm parts fit through without jamming,
but even so, the rim hole tends to be on the larger side,
which sometimes causes valve rattle.
Now, with threaded valves,
the part that matches the diameter of the threadless valve is the tip of the threads.
So if a half-threaded valve simply adopted the dimensions of both threaded and threadless versions as-is,
the valve nut wouldn't be able to pass over the threadless section.
In reality, that's not what happens (the valve nut does pass through),
so the unthreaded section of a half-threaded valve
is noticeably thinner than 6mm.
Because of this, even with high-quality pump heads,
the head frequently slips off during inflation.
In fact, with those UST tubeless valves I mentioned earlier,
a customer asked if they could swap them for another brand.
I've confirmed that Stans valves work pretty much fine,
but the OEM valve is contoured to fit snugly against the rim's outer bead radius,
so I still think using the original is preferable when possible.
Addendum: I received a comment saying that a Panaracer tire pressure gauge doesn't function properly.
Yeah, that would make sense.
Especially with cyclocross bikes where you want fine control over tire pressure,
half-threaded valves (including tubeless types) might be best avoided.
The image above is the pump head we use on our shop compressor
for old Silica disc wheels,
and even that leaks around the head.
Half-threaded valves are the only type where that happens.
Specialized (Roval) tubeless valves
are also half-threaded, which I suppose can't be helped,
but the fact that their regular WO tubes also have this design bothers me.
Apparently they don't cut full threads
because they're worried about the valve breaking at the thread root,
but I wish they'd consider whether accommodating that rare failure mode
is really worth making inflation difficult in everyday use.
"Valve threads damage pump head seals"
is another reason given for half-threading,
but because of that, the pump head grip is so weak to begin with
that you have to squeeze the cam lever hard to get a good seal and compress the packing,
which seems even worse for the packing if you ask me.
If you want to avoid damaging seals while still getting good grip, you'd think
but that can't be used on tubeless valves where threading is essential.
By the way, I'm asking that applause for this post only come from people
who've actually experienced that weak pump head grip with half-threaded valves.
If we hit 300 applauses, I'll do a 700×18–26C tube sale at ¥300 (tax included).
So why is it so hard to pump air into this valve?
It's because the threads on the valve are only cut halfway around.
Specialized tubes—which aren't tubeless valves but regular tubes—use the same design.
I'd been planning to write about this eventually, so I had images in stock
(though the image above is actually from a Specialized tubeless valve).
I don't know if they think it looks cool or what,
but with these types of valves, the pump head's grip is abnormally weak,
causing air to leak around the head or—once pressure builds up—the head pops off with a bang.
French valves come both with and without threads cut into them.
But except in cases like tubeless valves where screwing the valve nut onto the rim is essential,
the valve nut isn't actually a functional component.
Since it's not functional, threadless valve designs exist.
When I measured the outer diameters of both types, they came out to just under 6mm.
The rim's valve hole has an inner diameter of just over 6mm.
I think tolerances are set so that nominally 6mm parts fit through without jamming,
but even so, the rim hole tends to be on the larger side,
which sometimes causes valve rattle.
Now, with threaded valves,
the part that matches the diameter of the threadless valve is the tip of the threads.
So if a half-threaded valve simply adopted the dimensions of both threaded and threadless versions as-is,
the valve nut wouldn't be able to pass over the threadless section.
In reality, that's not what happens (the valve nut does pass through),
so the unthreaded section of a half-threaded valve
is noticeably thinner than 6mm.
Because of this, even with high-quality pump heads,
the head frequently slips off during inflation.
In fact, with those UST tubeless valves I mentioned earlier,
a customer asked if they could swap them for another brand.
I've confirmed that Stans valves work pretty much fine,
but the OEM valve is contoured to fit snugly against the rim's outer bead radius,
so I still think using the original is preferable when possible.
Addendum: I received a comment saying that a Panaracer tire pressure gauge doesn't function properly.
Yeah, that would make sense.
Especially with cyclocross bikes where you want fine control over tire pressure,
half-threaded valves (including tubeless types) might be best avoided.
The image above is the pump head we use on our shop compressor
for old Silica disc wheels,
and even that leaks around the head.
Half-threaded valves are the only type where that happens.
Specialized (Roval) tubeless valves
are also half-threaded, which I suppose can't be helped,
but the fact that their regular WO tubes also have this design bothers me.
Apparently they don't cut full threads
because they're worried about the valve breaking at the thread root,
but I wish they'd consider whether accommodating that rare failure mode
is really worth making inflation difficult in everyday use.
"Valve threads damage pump head seals"
is another reason given for half-threading,
but because of that, the pump head grip is so weak to begin with
that you have to squeeze the cam lever hard to get a good seal and compress the packing,
which seems even worse for the packing if you ask me.
If you want to avoid damaging seals while still getting good grip, you'd think
but that can't be used on tubeless valves where threading is essential.
By the way, I'm asking that applause for this post only come from people
who've actually experienced that weak pump head grip with half-threaded valves.