Repeated flats, yet no puncture. A puzzler.

[elocs]

My 19 year old goddaughter has a cheap Walmart bike, fat tires. A few weeks back she got a flat in the rear tire with the brake pads totally locked onto the rim to where the wheel would not even move and the inner tube coming out of the tire.

I no bike mechanic, but I have changed bike tires for 50 years now and so I thought it wouldn't be a problem. There were no loose spokes so I just got a new tube and it was fine. Until a few days later, then flat again.

This time upon checking in the tried and true manner of holding the tube in a sink full of water I found a puncture. This time I got a self sealing inner tube and it was fine.

Now the rear tire has gone flat again. First it took a day to loose all the air, then a matter of minutes upon riding. I just got the tube off and checked--no sign of a puncture (but it is a self sealing tube and I've never used one before). I can see nothing on the tire or rim that could have caused the leak and again, the spokes are all tight.

What could be causing this tire to totally lose its air within minutes of riding when there is no apparent puncture? Does it need a new tire?

I'm flummoxed so any help is appreciated.

[nfmisso]

I would do the following:
1. tension and true the rear wheel spokes.
2. new rim tape (rubber band like thing that covers the ends of the spokes.
3. new thorn resistance tube - forget about the sealant, it does not seal, just slows down the leak a little.
4. tire liner: http://www.amazon.com/STOP-Flats-Bicycle-Tire-Liner/dp/B001CK2FM8/ the SLIME brand ones have sharp ends, and some times cause punctures or blowouts.
5. new tire with kevlar belts for flat protection.

As you know, partially inflate the tube, shove the tire liner into the tire, then the tube, then mount on the wheel, starting with the valve stem. Do NOT use tools for mounting the tire. Let a little air out as required to get the tire fully on. Make sure the valve stem is vertical, then pump up to about 10 - 20 psi; go all the way around the tire twice to squeezing it hard to make sure the bead is seated - you here little pops as you do this. then inflate to the recommended pressure.

Some people like to use a dry lubricant, some wet, some none. I usually use baby powder, as that is how my parents taught me. Not sure it makes any difference.

[elocs]

(08-01-2011, 10:23 AM)nfmisso Wrote:  I would do the following:
1. tension and true the rear wheel spokes.
2. new rim tape (rubber band like thing that covers the ends of the spokes.
3. new thorn resistance tube - forget about the sealant, it does not seal, just slows down the leak a little.
4. tire liner: http://www.amazon.com/STOP-Flats-Bicycle-Tire-Liner/dp/B001CK2FM8/ the SLIME brand ones have sharp ends, and some times cause punctures or blowouts.
5. new tire with kevlar belts for flat protection.

As you know, partially inflate the tube, shove the tire liner into the tire, then the tube, then mount on the wheel, starting with the valve stem. Do NOT use tools for mounting the tire. Let a little air out as required to get the tire fully on. Make sure the valve stem is vertical, then pump up to about 10 - 20 psi; go all the way around the tire twice to squeezing it hard to make sure the bead is seated - you here little pops as you do this. then inflate to the recommended pressure.

Some people like to use a dry lubricant, some wet, some none. I usually use baby powder, as that is how my parents taught me. Not sure it makes any difference.

Thanks. I've still have the tube out and with some air in it and can see no sign of any puncture. I cannot see anything on the tire, or in the tire, or anything coming through the rim liner, as well as no loose spokes, yet last night after filling the tire it was flat after less than 5 minutes of riding.

I just checked the tube again in the water and nothing. I can't tell if it's a valve problem or not but there is no air coming from that either. Could this be a result of a poor tire? Like I said, with the initial flat her rear brakes had totally seized up on the rim and the tube was sticking out of the tire, so may it be the tire that is not properly sealing? (I have always remounted my tires with new tubes by hand.)

I don't want this tire to seemingly be fixed again and then have her off somewhere and end up with a flat again. She has had more flats in a months than I have had in 3 years.

[DaveM]

The tube is what holds the air, the tire does not "seal". However, if the tire is not mounting onto the rim properly, it can slip off under pressure and let the tube blow out. I don't think this is what is happening because this will make a large hole in the tire, but just so you know to check to make sure the tire is seated on the rim evenly all around.

Very small holes can be hard to find in a tube, even with water. But if it is going flat in minutes or even a day or two, there is a hole somewhere or a faulty vale (pretty rare). If you really want to find it, put a lot more pressure in the tube (so it really gets big) and put it in water again.

I would double check the rim tape again. Maybe even put a layer of electrical tape over it for good measure. Carefully inspect the whole interior of the rim. Particularly on cheaper bikes, sometimes there will be small burrs or rough spots that will cut through a tube. You can usually sand these out. Check the hole the valve goes through too, very common to have the edges of the hole be sharp. Next, really check the inside of the tire. Feel with your hands on the whole interior surface. If a tiny wire or piece of glass is still wedged in the rubber, it may be popping the new tubes you are putting it. Look over the outside too and carefully pick out anything lodged in the rubber. This is a common cause of repeat flats.

[Zelpo]

I'd start with insuring that the right tire & tube size are being used for the rim. Tube coming out the side sounds extreme, over pressurized? tire not fitting correctly? Puzzling! Being that tubes are pretty reasonable, I'd replace that first, as well as inspecting the rim & tape.

Recently picked up a used bike, flat the other morning showed a hole on the bottom of the tube? Turns out there were some manufacturing burrs left on the spoke holes. The stock/thin rim tape didn't do a good enough job. I used the smallest rat-tail file I could find and two stages of different grit emery clothe to sand down the high points. Nice & smooth now. Something to check on these cheap wally-mart types of bikes, which the one I bought used & working on is