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Recurrent Flat Tires--help please!

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Recurrent Flat Tires--help please!

Old 04-25-15, 07:14 PM
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kb1989
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Recurrent Flat Tires--help please!

Hey everybody,

I ride a Cannondale Adventure 3 women's hybrid, and the last few weeks I've had a string of flats I can't explain. About three weeks ago, I got a flat on my front tire right on the sidewall of the Schraeder valve. I patched it, and carefully checked the entire tire for glass, etc, including the rim. Found nothing. Got a flat in relatively the same place a week later, at the exact spot where the valve is, but on the other side of the tire. I am starting to think it has something to do with the rim pinching the tube at this point, so I try to file down the rim hole with sandpaper (which is sharp), and that doesn't go great. To stop the problem I put on a new front tube with a Presta valve that is metal all the way down to inserting in the tube. Front tire flats stop for the next two weeks to the present. But I get a back flat, and this time find a thorn. Figure its a freak of spring, swap out the tube with a new spare, and ride carefully the next few days. And tonight I go to my bike to find a rear flat after I rode for 20 minutes only yesterday. What could be going on?

-I tend to ride to finger pressure PSI (ie I can kind of push it in a tad, but the tire is still firm, bc my pump doesn't have a gage).
-The tires are Kenda Kourrier 700cx38-45c that came with the bike, do they just suck? They are hybrid mixed not-road-slicks-and-not-knobbies.
-I am new at repairing tires, so it could be user error.
-We have had a lot of tree trimming around are apartment complex the past week, is this just bad luck (sticks, thorns, etc)?

Thanks for any ideas and help!
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Old 04-25-15, 07:32 PM
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It's not too uncommon to pinch a section of inner tube under the tire bead when reinstalling the tire following a puncture repair. When this happens, the tire may hold air for a period of time but generally goes flat in relatively short order. Often, but not always, this type of flat can be identified by two small parallel slits in the inner tube. There is no way for me to tell if this is your problem or not.

If that is your issue, the solution is to be more careful when reinstalling your new inner tube. I inflate my new inner tube with just enough air to give it shape and install it into the tire while the tire is still completely off of the rim. Then I carefully install the tire, one bead at a time onto the rim and check it all the way around on both sides before reinflating the tire to operating pressure. All that effort takes a little more time but I think that it pays off in the long run.
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Old 04-25-15, 08:51 PM
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Three common causes of flats:

1. 'Snakebite' flats are caused by insufficient tire pressure. If you hit a sharp bump, the tire is compressed all the way to the rim, resulting in blunt-force to the tube causing two small holes, usually a half-inch to an inch apart.
Cure: inflate the tire more.

2. 'Pinched tube' flats are actually a blowout. When you put the tire back on the rim, sometimes the tube can get caught between the tire bead and the rim. This most commonly happens near or at the valve stem, since the reinforced area of the tube can be wider than the bottom of the rim, and prevent the tire from seating. This type of flat will usually result in tearing the tube, sometimes with a straight tear, sometimes with a star-shaped explosion mark.

Cure: After assembling the tire, inflate it just enough to give it shape - maybe 5 psi. Next, push the valve stem all the way in, so it hits the inside of the tire, and let air pressure push it back out. Then patiently work your way around both sides of the tire, pushing it away from the rim and looking down in. You should be able to see the rim strip. If you see tube poking out, fix it. The end result is that you make sure the tube is all up inside the tire before you inflate it the rest of the way.

3. Puncture flats are caused by glass, thorns, etc. After fixing the tube, run a glove (not your bare fingers) around the inside of the tire to make sure the offending item is gone, then reassemble and reinflate per (2.) If you use your fingers to search for glass bits, you can tell you found one by following the blood trail.
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Old 04-25-15, 09:10 PM
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Another trick is carefully remove the flat tube eithout moving the tires position. If the flat hole isn't obvious, use your pump to inflate the tube until you find the hole. Then using the position of the stem, match the tubes holto the exact spot on the tire. Check the inside of the tire especially. You can have a piece of embedded glass or little metal slivers in the tire that a cause another flat later.
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Old 04-26-15, 11:23 AM
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kb1989
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Thanks for the tips, everyone! I will try to be more careful in my movements and hope that solves the problem. Cheers.
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Old 05-02-15, 09:02 AM
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A band-aid is a thorn resistant tube. They are five times heavier, but for my commuting worth the slight lose of acceleration for the added protection. In my experience, sealant (for example SLIME) does not work; it just gums up the valve.

Another thing; be careful removing the pump chuck from the valve - hold on to the valve stem with one hand, pull the chuck off with the other to minimize the force going into the valve stem.
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Old 05-02-15, 10:20 AM
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Originally Posted by kb1989 View Post
so I try to file down the rim hole with sandpaper (which is sharp), and that doesn't go great.
Instead of using sandpaper, I put a piece of masking tape over the inside of the valve stem hole then push a pencil through it.
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Old 05-05-15, 09:44 PM
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In case none of these tips help out, remember it's also possible you are simply getting unlucky. Believe it or not I think everyone who rides regularly gets a couple strings of flats. Don't worry, maybe you're just getting the next five years worth of flats out of the way all at once!

P.S. - If you put a Presta valve into a rim drilled for a Schrader valve without a spacer for the valve you can get pinching around the base of the valve stem, so that might be the issue with your latest flat.

Last edited by yuoil; 05-05-15 at 09:49 PM.
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Old 05-07-15, 05:02 AM
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One remote possibility is that the stem isn't sitting flush in the bottom of the rim. This can leave a gap between the base of the stem and rim into which the tube can bulge and fail.
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