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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 03-10-08, 08:40 PM   #1
lason
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front tire constantly flat

every time i go to ride my bike i find my front tire is flat. i've taken the tire off and there are no leaks in the tube and no punctures. i'll pump it back up and a few hours later it's flat again. the back tire is fine however. i keep my bike in my garage and it has been pretty cold lately so i wonder if that has something to do with it. i was hoping someone more knowledgable than me could provide some insight as to why this keeps happening.
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Old 03-10-08, 08:48 PM   #2
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Does your rim tape cover all of the spoke holes? If not, replace it. Try turning your tire inside-out and examine it under a strong light. Sometimes very small wires, thorns, glass, etc. can bury themself just under the inside layer and won't come out to do their mischief until you put some pressure on them. The other possibility is you may be pinch flatting the tube. That's squeezing the tube between the tire bead and the rim. If you're using the same tube and it still goes flat, fill it up partially and submurge it under water to find an "invisible" leak.

Tires will lose some air over time, but usually only a few lbs./day, then stabalize and lose air more slowly. Generally, they'll hold perhaps 50% of their air for a month or two. How often do you ride?
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Old 03-10-08, 08:57 PM   #3
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Have you checked to make sure the valve core is tight?
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Old 03-10-08, 09:01 PM   #4
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Have you checked to make sure the valve core is tight?
Thanks, I forgot that one!
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Old 03-10-08, 09:09 PM   #5
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Even if the valve core is tight, it could still be fouled with crud. Or Slime! You haven't been using Slime have you? Could be rust in there or could be dirt also. I used to work in a car tire place and we would put some spit on our fingers and them rub it over the end of the valve to get a film and then look for that film to bubble out. Not pretty, but it works.

In addition to looking at the inside of the tire under a strong light, you could run your fingers slowly against the entire inside of the tire and feel for a sharp point.

Bike tubes do loose air normally. They are not like car tires that hold air for seemingly ever. Some faster than others.

Also, I have had many, many tubes that came from the factory with slight leaks at the seams.

The definitive test for a tube is the old dunk test. If there is a leak, valve or tube itself, it will find it.

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Old 03-10-08, 09:19 PM   #6
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there shouldn't be any punctures because i have tire liners. i used to use slime but i don't any more and i haven't put any in these tires. i may have to try putting it in water, that's not something i would have thought of.
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Old 03-11-08, 01:28 AM   #7
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The "old bathtub" is the first place I go to check for small leaks!
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Old 03-11-08, 03:23 AM   #8
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Large saucepan. Dunk the valve, too. Often missed. Check particularly where the join in your tyre liner is. Could be an abraded section of the tube from the sharp edges of the liner moving ever so slightly as the tyre rotates. This actually would be my bet.
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Old 03-11-08, 03:44 AM   #9
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Dude, just get a new tube. They're $5.
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Old 03-11-08, 07:09 AM   #10
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I would consider it 3.95 well spent also, but lets not make that judgment for the OP. I applaud anyone's effort to save a penny and stick it to the man. It makes no economic sense, but some things are not about that. Particularly when it comes to bikes.

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Old 03-11-08, 07:47 AM   #11
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Dude, just get a new tube. They're $5.
+10
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Old 03-12-08, 04:10 AM   #12
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You know, new tubes are OK, but if you don't know what's causing the original one to deflate, you're just wasting money putting a new one in. Duh!
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Old 03-12-08, 04:57 AM   #13
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Plus thinking green, a patch is probably better than a tube.

I usually toss my tubes, but I'm just saying...
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Old 03-12-08, 10:53 AM   #14
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i have a spare tube so that's not a problem. the tire has actually retained the air i put in it a few days ago. i have no idea why it's so finnicky but it's working now.
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Old 03-12-08, 11:18 AM   #15
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Yeah, good luck hearing or feeling a 2 hour leak. Dunking the tube to find the leak is the only way in those cases.

If this is truly an intermittent leak then there's a very good chance it was caused by gunk in the valve. Do you use the valve caps all the time? I know that some think they are just there to avoid a valve stem puncture while the tube is in the box. But the caps also help by avoiding dirt getting on the end of the valve and blowing into the tube the next time you fill up the tire.
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Old 03-12-08, 11:19 AM   #16
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grit in the valve that finally blew into the tube....................
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Old 03-13-08, 02:18 AM   #17
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not using latex tubes, are you? they leak air and are essentially flat overnight. much lighter in some cses and a smoother ride with less rolling resistance, but leaky. mine go from 120 to 20 psi in about 15 hours.

most cheaper tubes are the butyl rubber type (geneally black in colour). these hold air much better, especially if the valve is properly inserted in the valve tube and ther's no grit around the seal.
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Old 03-13-08, 06:48 AM   #18
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I was thinking of starting this same thread until stumbled into this one. I'm having this exact problem except I am on my third tube in a month and still flat. I have examined the inside of the tire and can't seem to find anything. I'm now to the point of buying another tire. The one I got will hold air long enough to get a short ride in, but I just don't feel comfortable on it. The tire about 1000 miles on it (Continental Attack) any idea how many miles you should get out of a set of tires like these?
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Old 03-13-08, 07:53 AM   #19
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I suspect something in your tire.

I had a situation where my front tire went flat twice in two days. Now i know how to fix a flat and I ran my fingers along the inside of the tire after the first flat and found nothing, so i fixed the flat and off i went. After the second flat in as many days, again i felt the inside of the tire and found nothing. However my suspisions told me something was wrong since it wasn't a pinch flat and the hole was on the onside of the tube where it makes contact with the tire. This time i scrutinized the tire in the location of the hole by flexing it and sure enough i found a small piece of glass that was actually imbedded in the tire.

The moral of the story: Line up your tire label with your stem so that you can scrutinize your tire in the area of the leak.
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Old 03-13-08, 08:20 AM   #20
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I suspect something in your tire.

I had a situation where my front tire went flat twice in two days. Now i know how to fix a flat and I ran my fingers along the inside of the tire after the first flat and found nothing, so i fixed the flat and off i went. After the second flat in as many days, again i felt the inside of the tire and found nothing. However my suspisions told me something was wrong since it wasn't a pinch flat and the hole was on the onside of the tube where it makes contact with the tire. This time i scrutinized the tire in the location of the hole by flexing it and sure enough i found a small piece of glass that was actually imbedded in the tire.

The moral of the story: Line up your tire label with your stem so that you can scrutinize your tire in the area of the leak.
Also mark you tube with a permanent marker so that you put the tube in the same orientation when you put the tire back together. This is particularly handy for those slow leakers. If you end up with more then one patch in the same place, look for the poker

I pump my tubes up so that they are about double the size (cross section diameter) of normal and then dunk them to find the leak. If it a slow leaker, you may have to move very slowly and knock the bubbles that normally form on the tube off to see if any new ones form.
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Old 03-13-08, 09:07 AM   #21
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Quote:
Originally Posted by lason View Post
every time i go to ride my bike i find my front tire is flat. i've taken the tire off and there are no leaks in the tube and no punctures. i'll pump it back up and a few hours later it's flat again. the back tire is fine however. i keep my bike in my garage and it has been pretty cold lately so i wonder if that has something to do with it. i was hoping someone more knowledgable than me could provide some insight as to why this keeps happening.
You find no leaks or punctures. (I'll assume that you are checking under water) You did not say if you rode the bicycle before it went flat again. If you did, then a surprisingly common failure mode is failure to screw the nut back down on a presta valve. Normal riding will cause the valve to unseat (vibration etc) often enough to bleed air. Other than that, bad stem/valves cause as many slow leaks as holes in the tube.
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Old 03-14-08, 10:38 PM   #22
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well, i found the leak. it was the valve that was slowly leaking. the tire wasn't punctured at all. it wasn't until i changed the tire that i found that the other one was leaking. i tried dunking it in the tub but i didn't see any bubbles. it wasn't until i hung the tire over the shower pole that i heard air hissing out. i tried pumping it up to see if i could pinpoint the leak and that's when i found it. thanks everyone for your input. i thought i had a phantom leak! i wonder what could have caused it. anyway, hopefully the new tire will last a while (at least until the weather picks up so i can go out riding)
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Old 03-14-08, 10:54 PM   #23
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On a Schrader valve, there is a little removable insert that can be taken out, and it can be loose. You can also get crud in there that keeps it from closing right. (We used to remove the insert to deflate truck tires, much quicker that way- and will actually form frost on the valve stem while deflating).
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Old 03-14-08, 11:11 PM   #24
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nevermind, i found a slight tear in the tire that was next to the valve. that's what was causing the leak.
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Old 03-15-08, 10:35 AM   #25
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Originally Posted by Pig_Chaser View Post
I suspect something in your tire.

I had a situation where my front tire went flat twice in two days. Now i know how to fix a flat and I ran my fingers along the inside of the tire after the first flat and found nothing, so i fixed the flat and off i went. After the second flat in as many days, again i felt the inside of the tire and found nothing. However my suspisions told me something was wrong since it wasn't a pinch flat and the hole was on the onside of the tube where it makes contact with the tire. This time i scrutinized the tire in the location of the hole by flexing it and sure enough i found a small piece of glass that was actually imbedded in the tire.

The moral of the story: Line up your tire label with your stem so that you can scrutinize your tire in the area of the leak.
There was a thread on here about the guy that ran his fingers round the tire to find the problem and found it was
broken off syringe needle! Good idea to look first, or use a rag.
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