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Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

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Old 12-26-05, 04:38 PM   #1
CycleDeac
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Constantly Flatting

I recently replaced the tube on my back wheel with a new one. Granted it was the first time I changed my tubes, I went slow to make sure I didn't screw up. I've done two rides on my trainer and after each I come to find that my back wheel has flatted again. It pumps up fine and I can't hear any air escaping when I pump it up. Any ideas? Thanks in advance.

CD
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Old 12-26-05, 04:49 PM   #2
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You can check for otherwise invisible / unhearable leaks by sticking the inflated tube under water. You will see tiny air bubbles if there's a hole in the tube.

As for what may have caused a flat... check your rim tape to make sure the spoke holes on the wheel are completely covered, and very carefully check the tire to make sure nothing sharp is jammed in there. Also, some folks swear by talcing their tubes (put tube in ziploc bag, put some powdered talc in there, seal, shake, done) to prevent the tube from sticking to anything (thereby causing a pinch flat).

Good luck!
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Old 12-26-05, 05:55 PM   #3
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I agree with Oboeguy - you've either got a peice of metal or something sticking through your tire and puncturing your tube or you've got a rim tape problem. Either should be pretty easy to figure out. Find the leak by putting the pumped up tube underwater. If it leaks on the inside, check the rim. If it leaks on the outer side, check for debris in your tire. For extra credit, when you put the tire back on the wheel, line up the logo/label with the valve stem, that way you can find debris in your tire much easier when you find a leak in your tube. Good luck!!
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Old 12-26-05, 06:02 PM   #4
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Quote:
Originally Posted by CycleDeac
It pumps up fine and I can't hear any air escaping when I pump it up. Any ideas?
Do you mean air leaks out slowly? on a new tube, I bet it's a bad valve. Dropping the tube in water will reveal the problem, whatever it is.
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Old 12-26-05, 06:43 PM   #5
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You need to find whatever is still embedded in your tire causing the flats.
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Old 12-26-05, 06:59 PM   #6
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yeah, it's worth getting good, cloth rim tape, like some Zefal, for eg

A friend of mine recently bought a Gitane and I couldn't believe how crap the rim tape was. He got 2 punctures in his first 2 rides due to the crap tape.
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Old 12-26-05, 07:03 PM   #7
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In addition to the excellent advice above, take the time to go all the way around the rim and look to see if there is any tube peeking out of the tire befoer you inflate. If there is, stuff it back in. Otherwise that tube is going to develop a leak or blow like a shotgun during inflation.
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Old 12-26-05, 09:49 PM   #8
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What are you using to pump up your tyre? Floor-pumps with locking heads only. No hand-pumps! You'll flex the valve-stem back and forth and rip the tube near the base of the stem.

Also pump up the flatten tube, find the hole and line it up with the tyre & rim at that spot. See if there's something in the tyre or a bad rim-tape job at that spot. Find the cause, don't just fix the symptoms.
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Old 12-26-05, 10:49 PM   #9
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+1 on Danno's comment. Also:

- check very carefully to be sure you don't have any burrs at the valve stem hole on your rim. If you do, a round file will smooth them out.

- don't use the valve stem retainer nuts. People have a habit of screwing them on too tightly, especially before inflating the tire. Recipe for a micro-tear....
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Old 12-26-05, 11:23 PM   #10
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Thanks guys. I'll try all this stuff out tomorrow and let you guys know how it goes.

Danno- I've been using a floor pump.

PPC- When I pump the tire up, it retains all the air. I can't hear any hissing or sounds coming from it. It's only at the end of my ride (on my trainer) that I notice that the tire is flat. I also noticed it was flat after it sat overnight by itself.

CD
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Old 12-26-05, 11:29 PM   #11
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one other thing: easy source of water for checking for slow leaks is an (empty) toilet bowl
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Old 12-27-05, 06:32 AM   #12
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Once you find the hole in the tube by using the water bath, as suggested, look for the source of the problem in the tube itself; often, you'll find a tiny shard of glass or such, often difficult to spot, embedded in the pinhole.

If nothing in the tube, look carefully at the corresponding spot in the tire (that's why you line up the valve of the tube and the logo on the tire, as Joe Dog said). If you can't locate the source by eyesight or by running your fingers around the inside of the tire, try running a cotton ball around the inside of the tire: the cotton threads may catch on a tiny protrusion that you might otherwise miss.
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Old 12-27-05, 11:42 AM   #13
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I've found it helpful to turn the tire inside-out. I've found tiny chards, cuts and thorns I couldn't easily find otherwise.
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Old 12-27-05, 01:23 PM   #14
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Also it's a good idea to always index the tire to the wheel. Convention is to line up the center of the tire label with the valve stem and on the right side of the bike. Doing this allows you to line up the leak in the tube with the tire, in case something in the tire is causing the problem.

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