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Road Bike Tire problem

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Road Bike Tire problem

Old 02-02-15, 12:08 AM
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Road Bike Tire problem

Hello everyone, i'm new here and i hope i'm posting this in the right place.

So i have a road bike; basically what happens is that the tires (the rear one especially) deflate right after i pump them up and start riding. They don't go completely flat, but rather become "half-inflated" and stay that way (i tested whether they go completely flat after prolonged periods of riding or not).

These are actually new tire tubes (front and rear) because leaks formed in the original ones and i had them changed. Those ones would get really deflated and i thought changing them out would fix the problem, i mean... well it alleviated the problem but i still have to ride with these deflated tires with completely take the fun out of having a road bike in the first place.

Another thing to note is that once a car bumped my rear wheel which had slightly deformed its shape but i had that fixed at the store (this was before i changed the tires). Dunno if that's relevant but it seemed worth mentioning.

Thank you all in advance for your time!!!
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Old 02-02-15, 12:15 AM
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Sometimes a sharp object either enters the tire and remains there, puncturing tube after tube, or is sticking in from the spoke side and doing the same thing. What you describe sounds like a slow leak. At high pressure the inner tube is pressed against the foreign object and air leaks quickly due the pressure difference between the outside air and tire air. As the pressure goes down, the tube "collapses" just enough to slow the leak and all is apparently well until you go to blow it up again. Take tire and inner tube off. Inspect the inside and outside of the tire for anything that is sticking through or floating about (don't neglect to inspect the sidewalls). Also inspect the wheel for anything that might be puncturing the tire from the inside. It is possible that that something might be under a rim strip.
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Old 02-02-15, 12:24 AM
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How fast after pumping to they deflate to that halfway state?

If it's very fast, it might relate to how you disconnect the pump, and you might be letting air back out again. Another possibility is a leak at or near the base of the valve. Once the pressure drops enough, the stress there might be relieved, and a tear might close back up. This is most common with narrow rims that don't allow the valve to seat properly.

There's no way to diagnose this at a remove, but what you might do, (after eliminating the pump removal issue, if any) is remove the tubes, and inflate to 2-3 times their relaxed inflated state, then look, listen or submerge to look for leaks. Be sure to wiggle the valve stem, to expose any leak near the base.
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Old 02-02-15, 09:24 AM
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Do these have Schraeder or Presta valves?
IF Schraeder, make sure the valve cores are tight.

What is the size of the tire and the pressures involved?
(real numbers)
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Old 02-02-15, 10:38 AM
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Old 02-03-15, 07:30 PM
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It has presta valve. And now that you mentioned it; i've noticed that the screw at the base (not the one i open to pump my wheel) is always loose. I tighten it every time before i pump but the next time i'm about to pump i find that it's loose again. Is it possible that the air is leaking from there?

I have no idea about the tire size and/or pressure but i'll check to give you the info.
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Old 02-03-15, 07:34 PM
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Are the tube liners that go between the tube and rim any good?
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Old 02-03-15, 07:38 PM
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Maybe the loose valve somehow tear up the tube around the rim hole. Riding with low pressure, pushing on the valve too hard while pumping and so on... Hard to tell.
I would just take the tube out, pump it a little, and submerge it in the water to see where bubbles are coming from. It may be from the tube itself, or from the valve. No need to ask more questions here...test it first, and you should find the problem yourself. Let us know.
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Old 02-04-15, 01:41 PM
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I had a similar problem. I marked the tire and tube both, then removed the tube. I submerged the tube in water and found the leak. Then I re-positioned the tube on top of the tire and marked the leak location on the tire. It took me three or four times around the tire before I finally felt the tiny tiny tip of a thorn or goat head in the tire. I got it out and haven't had a flat on that tire since.
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