so, i got some 404’s. the valve stem on the tube isn’t long enough to poke thru the rim, so i have to use a valve extender. i start pumping the it up, and when i’m done, the air gauge basically reads zero, but there’s obviously air in the tire. how do i get an accurate air pressure reading with this thing? do i just go by the spike in the air guage when i am pumping?
thanks!
Did you put teflon tape on the threads prior to installing the extender? This will help.
so, i got some 404’s. the valve stem on the tube isn’t long enough to poke thru the rim, so i have to use a valve extender. i start pumping the it up, and when i’m done, the air gauge basically reads zero, but there’s obviously air in the tire. how do i get an accurate air pressure reading with this thing? do i just go by the spike in the air guage when i am pumping?
thanks!
For a pressure gauge to read air pressure, the gauge must be exposed to the air under pressure. With Presta valves, this occurs when the pressure in the pump exceeds the pressure in the tube, thereby opening the valve by pressing the valve down. You can’t get a static reading with a simple valve extender that screws onto the valve: you need to press the valve down to release the air inside the tube. Valve extenders that either replace the valve core or contain a pushrod that presses down on the valve will work with gauges.
Get some longer valve tubes.
Ken explained it very well. Vittoria makes some nice ones with built in rubber o rings that obviate need for teflon tape. Just make sure you have removable core tubes/tires.
Like someone else said, make sure you have removable cores and just replace the valve with one of these (a few bucks on ebay TOPEAK brand):
FWIW, I had a Zipp front with one of these:
and had the same issue as you. I’ve had no difficulties after replacing the valve stems.
See Ken’s explanation.
FWIW, I use the type of extender that replaces the valve core (per Ken and see www.trisports.com to purchase) in my race wheels for this very reason. However, since I use a disc and carry only one spare I need the flexibility of being able to quickly remove the extender in the event my disc flats - for this reason i use the type of extender you seem to be using on my spare as it doesn’t require any tools or fiddling to remove.
I had one of those with the long post that would push the valve down, and canned it due to the incessant rattling. Now I just use my thumb on my deep front wheel: I’ll never lose my thumb, and I always have it around to lend to others.
It could be a bad check valve in the pump but if the pump works fine on other tires, it’s likely a bad seal at the valve extenders. Use a little teflon tape. I’ve also used thread sealant compound.
That doesn’t sound exactly right…as the OP was talking about not getting a reading after pumping, not using a pressure gauge. We all know the bouncing needle phenomenon where you are basically estimating pressure between readings of 200 and 60…
From my experience is that the problem is that extenders, particularly Zipp, are a different shape where the pump grips, so often they do not seal well and only really get air into the tire when the pump is pushing air out (pumping). Otherwise the air seems to leak from around the pump-extender connection. I don’t understand why extenders aren’t shaped exactly like regular presta valves. I am sure there is a reason, but it escapes me, and my pumps.