I have this problem I keep running into and it's getting pretty expensive. I've bought many inner tubes and when I pump the tire up with air, the inner tube fills up really good except in the area where the valve is. That area is still completely flat and I can't figure out why. I use a Presta valve adapter since I use a mini hand pump that doesn't have the Presta pump hole...could that be the problem?
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Clarification - you're pumping up a tube in a tyre on a bike rim and only part of the tube inflates? While the area around the valve remains soft an uninflated? If so, that's really odd.– Criggie ♦Commented Apr 9, 2017 at 1:36
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The tube is improperly installed somehow. 1) The Presta stem may not be pulled all the way through, 2) the tube may be twisted or folded near the valve, 3) (most likely) the tube is caught between the tire and the rim. Before installing the tube, pump it up until it just limply holds its shape -- not so much that it won't fit in the tire, but enough that it can't get twisted or trapped.– Daniel R HicksCommented Apr 9, 2017 at 13:01
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I thought it might be a twisted inner tube -- but it wouldn't make sense that the area of the valve would be underinflated. If anything, the valve would be over inflated and the rest of the tire underinflated.....– RoboKarenCommented Apr 10, 2017 at 3:42
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2 Answers
When you fill up an inner tube outside of a tire, the area near the valve will look a bit constricted because the rubber is reinforced in that area:
However, when you fill it inside the tire, don't worry - there's enough stretch in it so that it will expand to the right size and work properly.
The same goes for patches. If you fill the patched inner with air outside of a tire, the patches will deform the tube, but it'll still work just fine once in the tire.
answered Apr 10, 2017 at 0:41
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1I inflate tubes slight when applying patches, so that the patches do not stretch much when inflated to the full tire size. The patches also don't deform the tube this way.– Rider_XCommented Apr 10, 2017 at 1:54
The adapter shouldn't have an affect on whether the tire pumps up properly, or not. You might try pumping the tube up, before installing it. The tube could be sticking together at the junction. When the tube is outside the tire it can expand, and hopefully that junction at the stem will expand as well. Of course, you'll need to deflate the tube before installing it.
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1I definitely have had trouble with some Presta adapters and some pumps. The adapters attempt to be short enough that the pin in the pump chuck will press the center pin of the Presta valve, even though this is not necessary, and actually makes things harder to deal with. But in being so short they don't have enough length for many Schrader chucks to get a good hold. Commented Apr 9, 2017 at 21:52