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My wife has an old Moulton bike. I was inflating her tyres (small wheels, tyre imprinted ‘50 pounds’, when the rubber surround of the Schrader valve started inflating also.

It all seems quite airtight, but I don’t think it should do this, and I wonder why it is happening, and what I should do - replace the inner tube, or just let it get on with it?

I don’t want it to blow out when we are a few miles away from home.

Anybody seen this? Any thoughts and advice?

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    That is not normal. I would replace the inner tube Sep 30 '17 at 17:22
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    A picture would be good
    – Chris H
    Sep 30 '17 at 17:22
  • A blowout would be annoying, but you should be carrying a spare tube, pump, and required tools.
    – Criggie
    Oct 1 '17 at 2:28
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I haven't come across this before but it's not right. It sounds like the valve coating is coming unstuck from the metal part of the valve. If that fails it would be quite likely to fail suddenly which could be painful. Time for a new tube

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Well, you were quite right Chris H - I went out the next day to look at it, the tyre was flat, and the metal Schrader valve was hanging out of the tube at a crazy angle with the rubber bit that goes up the side of the valve split right open.

So I replaced the tube - a 20in Kenda 1 3/8 - with a Raleigh one. Nominally the same size, but as you can see from the picture, actually somewhat fatter, with 1.75 and 1 3/8 printed on it, though 1 3/8 is actually 1.375, of course.

Anyway, I got the new tube in OK - the tyre itself seemed fine - and it’s doing the job, so I guess there is some leeway in sizing.

The Raleigh inner shown is the spare, and has gone in the bike bag. The Kenda and its valve, after their moment in the spotlight, have gone in the bin, though I salvaged the valve cap. You can’t have too many valve caps :)

One again, thanks for all the help and suggestions.

enter image description here

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I'm guessing you have the sidewall of the tyre inflating sideways, and not the tube inflating through the valve stem hole.

Generally this is a failure of the tyre bead, and its no longer seating properly in the rim.

Also look at the sidewall for any form of tear, a couple of millimetres is all it needs to start stretching strangely.

If this is the case, you need a new tyre.

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