I got a new inner tube but it's letting air out

Question

I've tested the new inner tube overnight, to check whether it's letting air out, and it does. Is the tire damaged or the inner tube?

The tube must be leaking as the tyre doesn't hold air. It could be the valve. — Chris H, Commented May 6, 2017 at 8:46
If not that, then its either a faulty tube out of the box (it does happen) or your installation techniques have pinched the tube and put a hole in it. If so, treat as a puncture and patch it, then test, and reinstall carefully without pinching. — Criggie, Commented May 6, 2017 at 10:46
Remove the tube, fill it with air until it's slightly bulging, and hold it in a sink full of water. If you see bubbles it's leaking. (Note that it is common for a novice to damage the tube while installing -- read up on good installation techniques. Most important is to inflate the tube to where it limply holds its shape before installing.) — Daniel R Hicks, Commented May 6, 2017 at 11:45

Christian Lindig · Accepted Answer · 2017-05-06 08:49:09Z

This is hard to tell from the outset, but:

Have you checked the inside of your tire before you put it back on? If it contains a piece of glas it will puncture the new inner tube. Just remove it in that case. The only reason to replace the tire would be if it is worn down and for that reason you can expect to have another puncture soon.
You might have damaged the new inner tube when fitting it. You will need to take it out again and inspect it and it will become obvious, if that was the case.
The valve could be the problem especially if the loss of air is very gradual. Put the inner tube into soapy water to find the leak.

In summary: take out the inner tube, find the leak, and inspect the inside of the tire before putting in a patched or new inner tube.

You also replace the tyre if there is serious gashes, structure-compromising cracking, when the rubber feels like plastic after a long, LONG time, or when the tyre is mis-shaped to the point of no return, like bulging. — yollooool, Commented May 6, 2017 at 12:47

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