Originally Posted by
Andrew R Stewart
Second is that a fine piece of wire, which will produce exactly the nature of a slow (and I do call a many hour leak down a slow one) leak you describe. But a fine piece of wire is hard to see, find in the tire casing and feel if you only run your fingers one way along the casing's inside. Additionally if the wire is the same length as the tire casing is thick it will only get pushed against the tube with pressure, as in when riding, and might not extend into casing's inside when no outside pressure is present.
...I once managed to find a source of repeat leaks in a series of new tubes for a poor woman who was near the end of her rope. It was a relatively new bicycle (like the one described) and it turned out there were some aluminum shavings that had dropped out of one of the spoke holes (created doubtless by the original drilling).
There were three or four of them stuck underneath the rim strip, and only managed to gradually penetrate it and punch a very small hole in the interior surface of the tube where it met the rim strip. Each one had sharp ends, and the only indicator for where to look for them was in paying attention to how the tube had been installed in the rim, where they were located with respect to the valve hole, and that they were on the inner wall surface (facing the hub, not the tyre).
I think that was my most successful save, cause she was ready to toss the whole wheel.
Those Michelin wire things (as stated already) are tricky to find because they often stay buried in the tyre unless it's under pressure. Another good reason for paying attention to orientation when you take the tyre, tube, and wheel apart.