This Presta valve core, here removed, has been a nuisance since day one. Once inflated, it holds the pressure well for a trip to the trails, but after 3-4 days, the wheel is flat again. The volume (29"x2.5") is a lot to be lost so quickly.

bike stem core

It's anyway good practice to inflate the wheels every time one goes riding, but I'd much rather not see the rim on the ground with the chequered carcass pattern of the tire showing outside.

I've been tightening the core using a valve core tool. I'm torquing by hand only, as it seems too small and too fragile. If I tighten really hard, the rim will at least remain off the ground for two days, but still, too much pressure is lost.

I'm not sure I should be using a wrench, or even a torque wrench. How do I stop a removable valve core from leaking?

The rubber seal (black part in the picture) seems to be what holds the air inside. Should I pay particular attention to twisting the top nut after inflation?

(I'm using a foot pump and not a hand pump, and so inadvertently unscrewing the core while removing the chuck should not be the culprit.)

Update 1

The present question is a duplicate.

Update 2

Even if the valve core comes out clean with no sign of sealant deposit, as in the picture above, one may well still have a tubeless setup.

  • 1
    What makes you think it’s the valve core and not the tape, tire, beadseat, sealant, anything else?
    – Paul H
    Commented Aug 28, 2023 at 0:47
  • It indeed just occurred to me that I may simply have a hole in the inner tube. (They are tubeless ready, but since I see no liquid when I remove the valve core, there must be a tube.) Either way, I just switched the front and rear valve cores. I'll know tomorrow for sure whether the valve core is the problem.
    – Sam7919
    Commented Aug 28, 2023 at 0:50
  • 3
    You don’t even know if there’s a tube in? If the sealant was dried up or missing, none would come out of the valve.
    – Paul H
    Commented Aug 28, 2023 at 0:51
  • @PaulH I do know, verbally from the salesperson. But then I heard that some shops will do a really nice service by setting up tubeless-ready tires as tubeless before the bike leaves the store (the customer is asked to approve). What I do not know for sure is whether the shop did the nice service but omitted to ask me whether I want it (I want the option of switching back-and-forth studded tires for winter riding without mucking around with sealants, until I figure out—bicycles.stackexchange.com/q/79413/48599—whether a fatbike is really essential, in an attempt to n-1).
    – Sam7919
    Commented Aug 28, 2023 at 0:59
  • 1
    Wait. The shop told you it was tubeless. But then you heard other shops charge for tubeless conversion, so now you don’t believe the shop you bought it from? Have you tightened the valve’s lock nut at the rim?
    – Paul H
    Commented Aug 28, 2023 at 1:03

2 Answers 2


It’s unclear to me why you’ve removed the valve core. The valve core is the least likely culprit of this problem.

If you have a tubeless setup, I’d make sure the bead is sealed up, the valve lock nut is tight at the rim, the tape is sealing up the rim, and you have enough sealant to plug any minor holes in the tire.

If you have a tubed setup, why haven’t you ruled out a hole in the tube yet? Perhaps it’s near the valve.


Ignoring any other possibilities

Try putting in a core from another tube. Maybe it will work.


Throw in a small cup of tubeless sealant now the core is out. Usually seals up small leaks very well. Not much is needed. I like the Effetto foaming one, it's very runny, but use whatever you like.

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