Can't find puncture cause

Question

I'm changing my first inner tube after getting a puncture in the back wheel. I had to put the tube in water to find the puncture and it was a tiny hole on the inner side of the tube. On the wheel I can't see or feel anything that would have caused it. Any advice? Or do I just put a new tube on and see what happens?

Edit: Thank you all for your detailed advice. Looking at it again today I realise that it's not my finest hour - when I inflated the tube to check it out it's flipped inside out with the valve facing outwards. So the puncture was on the tyre side of it, not the wheel side. I still can't see what exactly on the tyre caused it, but at least it's less of a mystery now!

Answer 1

This is one reason why it's recommended that tires always be mounted with the label at the valve hole on the wheel - so you can find where the puncture was.

If the tire is still half-mounted on the wheel, or you did mount the tire with the label at the valve stem, you can easily find the only two places on the tire that correspond to the location of the puncture in the tube. It's usually accurate enough to use estimates such as "the puncture in the tube was about 1/3 of the way around from the valve stem, so the puncture in the tire has to be about HERE or HERE."

If that's not accurate enough to locate the puncture area, put the tube back in the tire, determine one approximate location, look there, and if you don't find it, flip the tube around and try again.

If that doesn't work, or if you didn't mount the tire or keep track of the tube orientation well enough to do that, you'll have to examine the entire tire for the puncture.

One quick way that's likely to find any foreign object poking through the tire is to run something over the inner surface of the tire and examine any area where something catches. Use something like a cotton ball instead of your fingertips so the location will be marked with a few cotton strands instead of skin and blood.

If you still can't find it, it's time to start a close examination of the entire tire's inner and outer surface. Flex the tire when you're examining any area so you can see if any cut or hole opens up.

Also - don't forget to check your wheel in the locations corresponding to the puncture in the tube.

Answer 2

Mystery punctures are irritating. If you suspect the cause was a pothole/sharp rock/edge, then its possible there is no cause embedded in your tyre. A hard railway-line crossing can cause them too, especially when under-inflated.

However you've said specifically "the inside of the tube" which I take to mean the side facing in toward your spokes. The common suspects here are one or more of

• Failing rim tape, either moving or wearing thin
• Sharp-edged spoke hole
• Long spoke poking through the nipple
• Shard of glass/wire/stone that was in the wrong place and fell out unnoticed

Andrew's suggestion about labels is great and you should absolutely do that. For a hole on the inside, lay the tube against the rim with the valve at the valve hole, and then measure around the rim. At most there will be a spoke hole on either side which is in exactly the right place, giving you a limited search area.

If you get more holes, simply replacing the rim tape is a good fix. If you can't get any, sticking a layer of painter's paper tape over the rim tape can buy you time..