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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 01-04-06, 08:36 AM   #1
eamonn_a
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Slow flat after tube replacement!

I had a slow puncture for months - the tyre took about a week to go down and I regularly had to pump it up before using the bike.

I finally replaced the tube the other day. I checked that the tyre was correctly seated after I'd replaced the tube and then pumped it up fully. It seemed fine. Definitely the correct size tube. I put the bike away, and took it out a few days later to find that the tyre was almost flat again!

Is it possible that there's something wrong with the wheel itself that is damaging the tube, and causing these slow punctures, or is it just a dodgy tube - unlucky coincidence? Any help would be appreciated. No point in replacing the tube again if the problem lies somewhere else!
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Old 01-04-06, 09:25 AM   #2
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If it's a road bike it is normal to loose pressure gradually until the tire is nearly flat. A five pound loss overnight is common. A 100 pound loss in a month or so is common. You should re-inflate your tires before each ride.
If you believe you are loosing air at an unusul rate inspect the tube under water to find the leak.

Al
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Old 01-04-06, 09:36 AM   #3
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Did you check your tire to remove the object that caused the flat in the first place?

Did you inspect the rim tape to see if it had been pushed over, or torn?

Did you check the valve stem to see if it was loose?

All of these things could cause an air leak in a new tube. If the leak is more than what the poster above pointed out, it is probably leaking from a puncture or valve.
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Old 01-04-06, 10:23 AM   #4
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Quote:
Originally Posted by Mchaz
Did you check your tire to remove the object that caused the flat in the first place?

Did you inspect the rim tape to see if it had been pushed over, or torn?

Did you check the valve stem to see if it was loose?
In my experience, the first is the culprit 85% of the time, the second 10% the third 5%, and a new tube being bad 1%.

These are not scientifically proven, and are guaranteed within + or - 10% each
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Old 01-04-06, 11:27 AM   #5
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Thanks. Much appreciated.
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Old 01-04-06, 01:01 PM   #6
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Pump up the old tube to find the hole that caused the small leak. Line up that hole with the rim & tyre and inspect in that area. Could be a piece of glass in the tyre. Could be a bad piece of rim-strip on the rim. Obviously with the tube off now, you've got two possible locations on the rim. And the tyre will have to be inspected in its entirety. Good luck!

BTW - what kind of pump you using?
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Old 01-04-06, 01:19 PM   #7
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If your rim strips are vinyl or rubber throw them away and buy cloth rim tape. Cheep rim strips can allow the spoke nipples to cut little nicks in the tube.Rim tape only cost about $3 per wheel. I use Pedros brand.
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Old 01-04-06, 02:24 PM   #8
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The subject of flats has come up a lot lately. Did you check the old and new tunes to see where the leak is? That can often give you a clue to the source of the problem.

If one or both are in the same spot on the outer circumference of the tube(s) (i.e., the surface that "interfaces" with the inner surface of the tire), check the corresponding point of the tire for a tiny shard. As I suggested in an earlier thread, run a cotton ball along the inside of the tire, as the cotton threads may catch on something minute that your fingers may miss.

If the holes are on the inner circumference, the problem may be, as others have said, a spoke hole/bad tape issue.

If the leaks are both at the valve, you may have a tendency to damage it while inflating your tubes or when removing the pump head from the valve stem.
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Old 01-05-06, 06:29 AM   #9
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Quote:
Originally Posted by DannoXYZ
Pump up the old tube to find the hole that caused the small leak. Line up that hole with the rim & tyre and inspect in that area. Could be a piece of glass in the tyre. Could be a bad piece of rim-strip on the rim. Obviously with the tube off now, you've got two possible locations on the rim. And the tyre will have to be inspected in its entirety. Good luck!

BTW - what kind of pump you using?
I'm just using some ancient old pump from the dark ages. Could this have anything to do with it? I'm not a serious cyclist - just use the bike to get around town mainly. It's a Trek hybrid - only about a year and half old.

I'll take your advice and check the two tubes - see if I can find where the problem is.

I think I've enough to go on now from everyone's responses! Thanks all!
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Old 01-05-06, 08:57 AM   #10
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Quote:
Originally Posted by Al1943
If it's a road bike it is normal to loose pressure gradually until the tire is nearly flat. A five pound loss overnight is common. A 100 pound loss in a month or so is common. You should re-inflate your tires before each ride.
If you believe you are loosing air at an unusul rate inspect the tube under water to find the leak.

Al
This is a nearly true statement if the tubes are of the ultra lite variety. I have riding friends that have experienced an increase in pressure loss when the went for the lighter higher dollar tubes. Air molecules actually do migrate through the tube membrane of the lighter tubes. They are more porous. I've never considered buying a tube that was 20-40 grams lighter and then putting up with the continual air loss. The tubes I use may not be any good, but they're cheap and when I top off the Vredestein tyres with the Kenda tubes at 120psi, I can go back a week later and they will still be within 5lbs or so of the 120. If I want to make up the 20 grams weight penalty, I spit out my gum before riding.
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Old 01-05-06, 10:49 AM   #11
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Quote:
Originally Posted by DannoXYZ
And the tyre will have to be inspected in its entirety.
Each and every time I take a tire off, I inspect it in its entirety. It's so easy to do, and saves potential headaches, so why not? And it's paid off plenty in the past finding thorns and staples that were just about to work their way in for a puncture about 10 miles from home.
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Old 01-05-06, 11:37 AM   #12
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you might be damaging the valve stem when you are pumping or attaching the pump.
I have done it myself. Some pumps are worse than others, especially hand pumps.
You must be careful to keep the valve stem vertical when you attach and while you pump.
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