Delayed Flat....tube size???
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  1. #1
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    Delayed Flat....tube size???

    Riding 40 mile round trip. At 21 miles while making a stop at cash station rear Serfas touring tire loses pressure from 80 to about 15. Sidewalk repair with new tube that has different dims than the 700/35 28 it replaced but still with presta valve. I think tube size was 700/32 25 and went in easily. Inflated to stable pressure and rode to fuel stop for air pump thinking all I would get would be 32-35lbs. But tire inflation reached hardness that I gauaged to be 80lbs. Finished ride, stowed bike in basement. Next am measured inflation at 100 and released some air. Next day couldn't ride, but this afternoon I went to mount up and the rear wheel was completely flat. Just for the record before installing new tube I inspected the rim and rim liner for any material that would cause a flat and both in the sun light available inspected the inside and outside of the tire. Nothing. I ran thumbs and fingers for a touch inspection the insideand outside of the tire. Can the air seep through a smaller tube because the poracity level of the tube has been inflated to a point beyond the capacity to hold air? Or is there still some unseen micro object inhabiting the tire or tube. .

  2. #2
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    All tubes leak air, the rate of air loss is dependent on the size of the holes. If there are no holes, those air molecules are pretty small and still somehow manage to get through the rubber molecules.
    I've had many new tubes that have had holes or slits in them right out of the box.
    So no mystery here, fix it and move on.
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  3. #3
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    No; the extra stretching of the tube would not be sufficient to cause the leak you described. Obviously, inspect everything again. My suspicion is the valve's base was poorly glued to the rubber tube. Plunge that sucker under some water and find the source.

  4. #4
    'brifter' is a lame word.
    Reputation: cxwrench's Avatar
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    You looked at the tire and the rim...sounds like you forgot to put some air in the punctured tube and find out what actually caused the flat.
    I work for some bike racers
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  5. #5
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    It could be any number of things including a tiny object you may have missed in your touch inspection inside the tire. If I get a flat, I go as far as turning the tire inside out and inspect the inside very carefully visually and tactily. Some sharp objects are very tiny and are only felt in one direction.

    Other items may be a defective tube (most likely at valve), an improperly installed tube or just another puncture - bad luck happens!
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

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  6. #6
    ngl
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    If you are at home try removing the tube, inflating it and then submerging it in a bucket of water. Locate the location of bubbles coming from the tube and determine what caused the hole.

    Generally, I put a small mark (or identify an existing mark such as a logo) on the sidewall on my tire. When I install the tire onto the rim I locate this mark directly above the valve stem hole. Once you've located (and determined what caused) the hole in the tube, match it to the proper location on the tire to see if there is a small sharp object still embedded in the tire. Otherwise, inspect the whole tire as Lombard stated above.

  7. #7
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    Step 2 Tube Inspection

    Quote Originally Posted by cxwrench View Post
    You looked at the tire and the rim...sounds like you forgot to put some air in the punctured tube and find out what actually caused the flat.
    Sidewalk repair included visual inch by inch. I did find an abrasion but no cuts, punctures, or air leaks I could listen to, but your reminder to go back and find the original cause seemed smart. I found a small puncture probably a piece of wire...however, the Serfas tire is supposed prevent such flats. The replacement tube was a Kenda 700/28/32 that replaced a serfas 700/35/50 both .9mm. The smaller tube had a leak 1 1/2" from the valve stem and appears to be a wear abrasion that allowed the seam to split. Perhaps the cause was over inflation but the smaller tube went flat because it couldn't take the pressure. Or is Kenda just a bottom of the shelf tube. So I have now installed an original sized Serfas tube after rechecking rim and tire and finding nothing. Was the 700/28/32 just too small and should never have been used

  8. #8
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    Nothing wrong with Kenda tubes.

    A smaller tube will be thinner when inside the tire. In theory, it will be more prone to punctures, but no more so than a "lightweight" tube.

    What size are the tires you're using?

    As far as your tires being puncture resistant, the key word is resistant, not proof. It is still possible for a wire to penetrate, just not as likely.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein



  9. #9
    Schuylkill Trail Bum
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    Quote Originally Posted by cxwrench View Post
    You looked at the tire and the rim...sounds like you forgot to put some air in the punctured tube and find out what actually caused the flat.
    ^^^

    Nailed it.

    No pun intended.

  10. #10
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    Quote Originally Posted by contract truckman View Post
    Sidewalk repair included visual inch by inch. I did find an abrasion but no cuts, punctures, or air leaks I could listen to, but your reminder to go back and find the original cause seemed smart. I found a small puncture probably a piece of wire...however, the Serfas tire is supposed prevent such flats. The replacement tube was a Kenda 700/28/32 that replaced a serfas 700/35/50 both .9mm. The smaller tube had a leak 1 1/2" from the valve stem and appears to be a wear abrasion that allowed the seam to split. Perhaps the cause was over inflation but the smaller tube went flat because it couldn't take the pressure. Or is Kenda just a bottom of the shelf tube. So I have now installed an original sized Serfas tube after rechecking rim and tire and finding nothing. Was the 700/28/32 just too small and should never have been used
    Size of tube is NOT the issue. The fact that your second flat appears to be cause by abrasion, leads me to ask the exact definition of this statement in your original post: "Inflated to stable pressure and rode to fuel stop for air pump." Not at all sure what "stable pressure means" but if you rode the tire when it was soft, the excessive flex in the tire could easily have abraded the tube. This would NOT have been caused by over-inflation.

    The bottom line for ANY flat tire is what cxwrench said: if you haven't located the source of the flat by inflating the tube, then you're likely to get another flat. Also, you are confused about the Serfas tire: it might reduce the likelihood of a flat but it most certainly will not prevent all flats. Only solid tires can do that.

  11. #11
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    Dunce cap for a bike helmet

    You are absolutely right. Bike pump I have been carrying for five year failed to inflate to a pressure much more than 20 lbs. Certainly would account for the area near the stem being an abrasion. I didn't consider this prospect because after a fuel stop inflation I rode 19 miles and let the bike sit for a day. But your assessment best fits the outcome even though the mileage to the fuel stop was less than 1/2 mile.

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