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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 01-05-06, 10:44 PM   #1
hester
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my rear tire keeps loosing air...

at a very slow pace, of course, but it happens. even while just sitting idle.

i bought the road bike and took it to the kitchen for a tune up. it was in decent shape and all i had to do was adjust the derailuer, set the brakes and lube it up. i also trued the front wheel, sort of as it was my first attempt ever, but i left the back wheel as is because it didn't seem too off and i had almost overstayed my welcome by truing for nearly an hour.

after about a mile and a half i noticed the back dragging and stopped at a bike shop which was luckily a block away. the back tire was completely flat by the time i got there. the guy replaced the tube and i found out there was no rim tape in either wheel. by the time i left, i obviously had spent much more than i planned...

since then, everytime i take it out i have to add air before i get going. it's not a constant flat, but there's always a definate difference in pressure between it an the front. both tires on the bike seemed to be brand knew when i got it and after the shop guy and i both checked inside for objects and found none, it still looses pressure.

could it be the truing that i neglected? what on earth could it be, i ask!
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Old 01-06-06, 12:47 AM   #2
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Quote:
Originally Posted by hester
since then, everytime i take it out i have to add air before i get going. it's not a constant flat, but there's always a definate difference in pressure between it an the front. both tires on the bike seemed to be brand knew when i got it and after the shop guy and i both checked inside for objects and found none, it still looses pressure.

could it be the truing that i neglected? what on earth could it be, i ask!
Either the rim has a rough spot, the tube has a slow leak, or there is something embedded in the tire.

1) Take the tire/tube off. Inspect the rim and spoke nipples for burrs. Make sure the rim tape is smooth and nothig is poking through.

2) Inflate the tube and hold it underwater in the sink. Look for slow/small air bubbles.

3) Take a cotton ball and slowly run it over the INSIDE surface of the tire. even the smallest of thorn heads will usually snag the cotton and reveal themselves.

Gotta be one of those three things......
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Old 01-06-06, 07:32 AM   #3
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All high pressure tubes lose air. The rate can differ between tubes, so that may account for the obvious difference between your front and rear tires. You should ALWAYS top off your tires before each ride.
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Old 01-06-06, 07:43 AM   #4
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I have found that if i inflate my cheep LBS tubes to 90 psi, they will be at 80 by the end of the day, but lucky for me.. they will hold 80 for 2 weeks straight and so far, I have not seen it drop below 80 at all !

WOOT !

now, on my wallysmart huffy, i had to top off the tube every single day... glad those days are over !!!!!! ( not for the refilling, but for the huffy ! )
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Old 01-06-06, 07:20 PM   #5
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One of the things I see that causes very slow leaks is tiny bits of steel belt material. These little pieces of fine wire work through your tire and can put very tiny holes in the tube. Hard to spot, too.
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Old 01-06-06, 07:39 PM   #6
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The needle inside the valve of the tube is adjustable with a pair of amall tweezers... Try tightening it a half turn or so and see if that helps.
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Old 01-06-06, 07:55 PM   #7
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you can expect tubes to lose about 10% per day. Always top off before starting a ride-

train safe-
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Old 01-06-06, 07:56 PM   #8
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The needle inside the valve of the tube is adjustable with a pair of amall tweezers... Try tightening it a half turn or so and see if that helps.
Your talking about Schrader valve right?
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Old 01-06-06, 10:16 PM   #9
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Originally Posted by bigbossman

3) Take a cotton ball and slowly run it over the INSIDE surface of the tire. even the smallest of thorn heads will usually snag the cotton and reveal themselves.
I never heard of that. That's a great idea!

Last edited by The Pontificato; 01-07-06 at 08:42 AM.
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Old 01-06-06, 11:52 PM   #10
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Quote:
Originally Posted by bigbossman
Either the rim has a rough spot, the tube has a slow leak, or there is something embedded in the tire.

1) Take the tire/tube off. Inspect the rim and spoke nipples for burrs. Make sure the rim tape is smooth and nothig is poking through.

2) Inflate the tube and hold it underwater in the sink. Look for slow/small air bubbles.

3) Take a cotton ball and slowly run it over the INSIDE surface of the tire. even the smallest of thorn heads will usually snag the cotton and reveal themselves.

Gotta be one of those three things......
thanks for the ideas, i'll look into it tomorrow. worst case scenario, if there's a rough spot in the rim, what's the course of action? do you have to ditch the wheel and get another or can it be located pretty easily and rubbed out?
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Old 01-07-06, 12:00 AM   #11
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i've never had a road bike before, so it's possible that this is a normal occurance, as a couple of you have said. i guess i'd better start keeping better track of the pressure coming in and out.

but does this mean i should start carrying cotton balls in my emergency kit? 'cause i don't think that extra weight will do me much good.
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Old 01-07-06, 11:26 AM   #12
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Originally Posted by Bikewer
One of the things I see that causes very slow leaks is tiny bits of steel belt material. These little pieces of fine wire work through your tire and can put very tiny holes in the tube. Hard to spot, too.
This is common, especially on century rides where you spend a lot of time on highways that trucks use. That's why I always carry cotton balls - they are EXCELLENT at ferreting out little slivers stell belt material.
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Old 01-07-06, 11:29 AM   #13
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Quote:
Originally Posted by hester
i've never had a road bike before, so it's possible that this is a normal occurance, as a couple of you have said. i guess i'd better start keeping better track of the pressure coming in and out.

but does this mean i should start carrying cotton balls in my emergency kit? 'cause i don't think that extra weight will do me much good.

Just toss a cotton ball in your patch kit. Little steel belt bits and thorn tips are a b!tch to find when you're sitting on your butt in road side dust and dirt. Either you'll be there forever, or you'll keep repairing/getting flats during the ride.

I'm telling ya, they work great!!
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Old 01-07-06, 11:30 AM   #14
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Originally Posted by hester
thanks for the ideas, i'll look into it tomorrow. worst case scenario, if there's a rough spot in the rim, what's the course of action? do you have to ditch the wheel and get another or can it be located pretty easily and rubbed out?

Depending on the rough spot, you can file or emery cloth it into submission.
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Old 01-07-06, 11:42 AM   #15
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Quote:
Originally Posted by hester
i've never had a road bike before, so it's possible that this is a normal occurance, as a couple of you have said. i guess i'd better start keeping better track of the pressure coming in and out.

but does this mean i should start carrying cotton balls in my emergency kit? 'cause i don't think that extra weight will do me much good.
Now that's weight weenieish!
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Old 01-07-06, 09:26 PM   #16
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Originally Posted by fordfasterr
I have found that if i inflate my cheep LBS tubes to 90 psi, they will be at 80 by the end of the day, but lucky for me.. they will hold 80 for 2 weeks straight and so far, I have not seen it drop below 80 at all ! ....
Funny, my $2.99 Performance tubes are stone hard after four weeks!
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Old 01-08-06, 08:16 AM   #17
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Quote:
Originally Posted by bigbossman
Either the rim has a rough spot, the tube has a slow leak, or there is something embedded in the tire...
Bigbossman is right again. One likely spot to look for a slow leak is at the Presta valve. I've noticed lately that several of my tubes have leaks at the seat of the valve itself (not on the rubber of the tube). Check for this by putting a drop of water/spit/liquid soap on the valve and see if you get bubbles.

Happy hunting!
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