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I'm replacing my inner tube after getting a flat. When I inflate the tyre with the new tube in, it feels soft- even though the pump says the pressure is 100PSI.

The tube inflates and holds its shape when I inflate it on its own (outside of the wheel). I'm convinced I'm making some fundamental error but cannot figure it out.

Details:

Old tube: Schrader 700X28-38C Specialized (came with the bike)

New tube: Schrader 700X28-45C Kenda "kwick-seal" and says e-ready. (only one I could find online because of lockdown).

The new tube valve is shorter than the old one. It also appears to leak a bit of fluid when I deflate and doesn't deflate easily when I push the pin. I'm using a track pump which I have tried on my girlfriend's bike and seems OK.

Any suggestions would be great as all my local bike shops are closed because of COVID.

  • How soft does it feel? Does it make a substial deformation when you sit on the bike? Can't you patch the old tube? – Vladimir F Apr 18 at 6:41
  • Yeah it's so soft that the rim would probably touch the floor if I sat on the bike. I initially patched the old tube, but popped it (caught between rim and tyre) when inflating. It's been a learning curve :) – smm Apr 18 at 6:59
  • OK. Is it also difficult to empty the tube completely (while pressing the pin)? Try to unscrew the valve (with something like in the second picture here bicycles.stackexchange.com/a/54837/21133 ). Is it clogged? If yes, try to make it open. – Vladimir F Apr 18 at 8:08
  • Ok, thanks. I'll try and find something similar to the second picture and give it a shot. – smm Apr 18 at 8:58
  • What's the bike? 28c-45c is a large inner tube if its a road bike. Usually 23c-28c. Make sure the tube is seated properly in the tyre carcass around the rim. You can do this by releasing the pressure and pressing the valve stem into the tyre – el_oso Apr 18 at 10:02
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Since you say the track pump's gauge reads 100 PSI, that suggests the air is pressurising inside the hose. I'd bet that it only takes a couple of pumps to get there too.

This means the valve is not opening to admit air into the tube, AND that the pump head is forming an airtight seal with the valve.

If its a Presta valve, make sure you back off the acorn nut on the tip of the valve.

If its a schrader valve, try depressing the pin in the middle. It could be that the valve seat is not moving when in the rim, though that's unlikely. Its also possible that some sealant has got the valve stuck closed, which would explain your difficulty in deflating the tube.
In this case, try to unscrew the valve core out of the valve, clean it, and then reinstall.

The valve core itself looks something like this:

enter image description here

and the tool to remove it needs to engage the two flats on the left side. You might be able to unscrew it with needle nosed pliers, but the proper tool looks something like this:

Park VC1


The new tube valve is shorter than the old one.

Could be that the valve stem is retreating inside the rim as you try to clamp the pump's head on. I feel this is not your problem, but adding for completeness.

If its Presta, fit the locknut. If its Schrader, then press a thumb hard into the tread of the tyre, outside of where the valve is, to stop it squashing into the rim. Once the tube's air pressure gets above ~10 PSI it should be plenty to hold the valve in the right place.

Another solution is to use an air pump with a thread-on head not a clamp-on one, if you have access to one. In the same vein, a CO2 based inflater can help, but they're expensive and only worth using if time is of the essence (like in a race or group ride.)


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  • Thanks Criggie, you've described exactly what's happening with the pump. 2 pumps and it's at 100PSI. Sealant now bubbles out of the valve when I (partially) deflate the tube, so I guess it's blocked up. Sadly I haven't got small enough pliers or the correct tool so will just reorder a new tube and wait... – smm Apr 19 at 0:13
  • You were also right about the valve stem retreating, but pressing really hard didn't change the outcome. – smm Apr 19 at 0:14
  • @smm thanks for the followup - much appreciated. Don't throw your old tube, save it for when you can get a tool. If nothing else it can be used to hang your bike from an overhead support, for working on it :) – Criggie Apr 19 at 0:29

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