How to find punctures in inner tubes?

Question

When I have a flat tire, I find punctures in inner tubes using three techniques, all starting with the inner tube outside the bike:

1. Hearing where the sound of air escaping originates.

2. Feeling the escaping air with my hand.

3. Putting it inside a container of water and seeing the bubbles. I end up using about 10 liters of water, and I have to rotate the inner tube to pass all of it through the water.

Is the method 3 smart? Could water get inside and damage the valve? All three methods seem to work very fast. Is this just a matter of taste or does some miss some punctures?

Answer 1

Do whatever works, really.

The problem with the container of water approach is that it requires a container of water. It won't damage the tube. Also, if you need to patch the tube, you have to wait for the wet tube to dry. So, I'd generally recommend doing this last (usually leaks are not subtle enough to need the immersion), but no harm going there first.

The usual technique I use is to try to blow up the tube a bit and put the tube near my upper lip if I can't find the leak by ear or feel it around the tube with my hands; the upper lip area is pretty sensitive, so its pretty easy to detect it. Try to be systematic about it, like start with the valve and go clockwise. If you jump around all willy nilly, you'll take longer to find it.

Sometimes you get leaks that are too slow for that, and generally in those cases, you end up replacing the tube anyway.

You can also trace the leak by checking near the valve (a common culprit; if its the valve itself in a Schrader valve, you can spit on it and check for bubbles) as well as running your hand along the tire to see if anything is there. If you make sure to align the label of the tire (e.g. where it says "Continental" or whatever) over the valve, its easy to work back to where the leak is if you find something (since the label and valve are in the same position, the position of what you found relative to the label tells you where the leak is on the tube).

See this page as well. It also covers what leaks mean stuff (if you have a thorn in the tire, chances are that's your cause, for example. Snakebites are often insufficient tire pressure. If you have a leak on the rim side of the tube, chances are theres something off with your rim tape, etc.).

Answer 2

To follow up on what Batman says, what you use to find the leak depends a lot on the circumstances.

If you get a flat by the side of the road (and you don't have a spare tube) then you obviously can't use the tub of water (unless you find a convenient pothole filled with rainwater). In other circumstances the water tub (or bathroom sink or whatever) is reasonably practical, but it may not be necessary.

First consider the circumstance. You're riding along and suddenly hear "Pfft, hiss, hiss, hiss..." as the tire rapidly goes flat. You can't ride home on the rim, and your spouse can't come and get you, so you need to fix the flat.

Even if you have a spare tube you should find the leak and check the tire at that spot for something embedded (or else your spare tube may be holed as soon as you inflate it). So you remove the tube, keep track of which side is which (if possible) and find the hole. Usually the way to do this is to inflate the tube with your pump and loop it over your head, as you rotate it around, listening for the leak. When you hear it, hold the suspect portion of the tube near your face to feel the wind blowing on it, to zero in on the hole.

Having found the hole (if possible, marking it with pen or chalk), you then lay the tube on the tire, aligning the valve stem with the valve hole in the rim (here is where it's nice to know which side is up, so you don't have to check both ways), and then check the tire in the vicinity of the hole for any embedded wire, nail, glass, or thorn.

Sometimes, though, a leak is hard to find by hearing/feeling it, either when it's too slow, or when it's so fast that the tire won't hold air long enough to listen/feel for it. In these cases a water tub is the way to go. The water tub is also handy for discovering valve leaks.

Answer 3

Not mentioned, but a technique that works best for me is to use my lips.

I've been an avid rider for 20+ years and have tried most everything to find those pesky little leaks. Water is good, but not always convenient. However, I always have my lips with me -- and I've found them to be sensitive enough to find even the smallest of leaks.

The technique is easy, just blow up the tube, place it around you head and rotate it ensuring that every part of the tube passes by your ever so slightly opened puckers. It there is a leak to be found, you will most likely find it that way.

Answer 4

If you do use a bucket of water, one thing that I was taught was to put a teaspoon of dish detergent (the foaming kind) in the water.

1) If the water you use is on the shallow side, the foaming or bubbles will help you locate the pin prick a bit better. This is especially important for slow leaks, such as valve leaks.

2) The soapy water will also help clean the area around the leak, so patches will adhere just a bit better.

Answer 5

Mostly to reply to your second question: I've had punctures/valve problems so small that when the tire is held under water it would take at least 10 seconds to form one bubble of air coming out. I could not feel this 'breeze' with my hands or lips. So I consider method 3 the most failproof as I don't know any other ways one would be able to find such a small leak. For the rest everything has been said by the other answers: if you hear the hissing there's no real need for any other method, on the road you might not have access to water or it's just inconvenient to patch so you're better of taking a spare tube and patch the punctured one at home.

Answer 6

I usually can't detect my punctures except using water. When I use water I discover that the puncture is tiny.

The bad thing about water is that you can't easily use that method in the field or on the road; and the good thing about tiny punctures is that you can wait until you get home.

Symptoms of a tiny puncture are:

1. Bike is fine when I put it away at night
2. Tire is flat when I get it out the next day

Or:

1. Discover that tire is flat when I'm riding
2. Reinflate the tire without fixing it, and steer towards home
3. Tire remains inflated for at least 20 minutes before it needs reinflating

Tiny punctures come from a tiny object embedded in the tire.

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If (only if) it were a bigger puncture, then I guess I couldn't reinflate without fixing it, but also wouldn't need water to find the puncture.

Answer 7

I find the most efficient way to find leaks in both tubed and tubeless tires (automobile) is to fill the tire with the recommended air pressure + 5 lbs for tubeless tires,(For an inner tube I fill it to 2 times its normal size, In other words, if you have a tube that is 2" wide when pressed flat, fill the tube until the tube is roughly 3" in diameter. If the tube is partially aired up, then just double its circumference. Don't worry too much about it popping. If you have ever seen one of these things filled to the point of catastrophic failure you would understand that most tubes will expand up to 4 sometimes six times the normal circumference. So keeping it at around double its operating size will ensure you won't pop your tube.

Before I air up the tire or tube, I locate an empty refillable spray bottle and add about a teaspoon of dishwashing liquid, then slowly fill the bottle with water so you don't fill the bottle with bubbles. I like to use the spray bottles that have a straight stream. The mist type creates fine bubbles that can work if the leak is big enough, but if it's a small leak, then it's like trying to find a needle in a haystack or in this case a bubble in a bubble bath. Also find a light colored crayon or wax pencil or even liquid paper so you can mark the location of your leak once you find it.

I normally run the back of my hand and fingers (the back of your hand and fingers are covered in small hairs that make it more sensitive to wind or air moving across them) around the outer ring or the part of the tube that faces the ground when you roll it. This is where most punctures occur from normal everyday riding. That changes if you are mountain biking or just off road for even a little bit. If so, you'll need to expand your search up the sides of the tube to be certain your leak is not there. Next, I check the inner ring (the side that faces the rim) If you find a leak here it is going to be either an equipment error or operator's error. The spokes of the rim should not be exposed to the surface of the tube. I know on older bikes there was a rubber belt/band that acted as a buffer between the rim and the tire, covering the spoke heads. Make sure there are no jagged surfaces on the wheel and spoke heads before reassembling your tire and wheel. //////CAUTION!\\ Before you go swooping your hand around that rim remember that what you are looking for is sharp enough to either have punctured or worn a hole in your inner tube, so be slow and use a light touch so you won't lacerate your hand or fingers. Do the same thing with your tire while you have the tube out of it (Again with CAUTION) to be sure you have removed any foreign debris or protrusions that have impaled the tire and was the cause of your flat or could be the cause of your next flat. After streaming the soapy water mixture onto the tire about a 6" section, pause for two to three seconds and if no bubbles have formed move to your next 6" section. Continue until you find the leak and when you do find it, grab your lite colored crayon, wax pencil or liquid paper and circle or "X" the spot where your leak is. Believe me, if you take your eye off of it, then look back at it, more often than not you won't be able to locate it without spraying it again.

I suppose you already know how to patch a tire so I won't walk down that road unless you need me to. To answer your question about the valve being damaged. Yes, water can damage the valve by oxidation. Just a small particulate of rust can cut or tear the rubber seal on the valve core. After spraying it to check for leaks and before I fill with air again, I use compressed air or even use the bike air pump to blow out the valve stem to clear it of water and debris. So I would say the way you've been doing it is good. The other answers offer some good tips also. It's one of those things that if you do it right, there are probably several ways to get the same result.
Happy Riding.

Answer 8

To prevent additional accidental puncturing the inner tube while moving it around to dip into water, I usually use my wet fingers to touch the inflated tube. It requires less water and leave the tube less wet for the repair action.

Regarding your concern that water may enter the tube, the air is going out because it is at higher pressure than the water, not because it is removed by buoyancy forces (like when you push an open and empty bottle under water). Therefore no water can enter trough the puncture

Answer 9

Finding leaking compressed air or gas from a tube or container is as much luck as having a sharp eye. The best technique I have found is to use simple dishwashing liquid (do not thin it out too much) and put a little over the areas in question. Luke submersion in water bubbles will form, but unlike underwater the bubbles stay (you have to wipe them away but you can get down to the actual hole (or holes) The added bonus is you were going to have to clean the area before applying any adhesive so once found and marked you only need to rinse the soap off and allow to dry.

Answer 10

The easiest method that always works for me is to over-inflate as @DJ Qu8ke mentioned, but then simply move my fingers and palm along the tube slowly but lightly, trying to 'touch' the leak. There must be some air escaping somewhere, or you wouldn't have experienced a flat or soft tire.

When you touch a leak, you can't actually seal it by resting a finger over it, but you do increase the speed of the escaping air, however weak it might be. What happens is that the pressure of the air in the tube has a constant positive pressure. So even if the leak is tiny, pressing on it with your skin causes resistance and deflects whatever stream of air is escaping.

The deflected air stream will hiss (which makes it a primitive musical instrument for those who are easily amused) even if it is faint. If it is a strong leak you can actually make it whistle. But those aren't the leaks that are hard to find.

Once you hear even a faint noise, you can 'echo-locate' the general area and search more carefully. Eventually you will find the location where lifting and replacing a finger over the leak will produce intermittent interruptions in the hiss and you'll know you have found the source.

However, when the leak is faint, you probably have discovered a weak area of the tubing, and so you should expect to find several of these leakettes. So cover each of them with a finger until you are able to decide that you can cover the entire area with a big patch, or that you will have to walk home with the bike on your shoulder.

Easy, and no artificial ingredients required!

Answer 11

One technique I haven't seen mentioned here is checking the outer tire. You need to do that anyway, to remove any culprit that caused to puncture and is still stuck, or you need to mend your tire twice.

First inspect the outer tire while still on the wheel. If that yields nothing, pop of one side of the tire off the rim and feel the inside carefully(!) with your fingers, taking care not to shift the tire along the rim.

If that yields nothing either, you continue using the various techniques described in other answers.