A few comments- If you're commuting using X lite tubes is not the way to get best reliability. I suggest you use standard thickness tubes. They cost less, are less likely to bleed down just sitting and withstand the slight ****** (stupid auto censor, let's try "pokes") and abrasions better then thin was ones. Running tires with penetration protection negates the more supple ride quality of the thin wall tubes anyways. 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. Lastly a barrier protection made of a woven fabric (as in Kevlar) is not much goos against wire as the wire will act like a sewing needle and poke past the fabric threads. A piece of glass/shard of flint will typically catch on a number of threads so will be stopped much more effectively. Last comment is how the fresh tube is inflated. If done with a CO2 device, as road side fixes are increasingly done with, there will be far quicker bleed down due to the CO2's greater ability to sweat through the tube, compared to atmospheric gases. If an ultra lite tube is used and a CO2 is used no surprise that a work shift will see significant pressure loss. I tell my customers to deflate the tire and reinflate with a pump (or compressor) twice if they did a CO2 inflation. This purges out the CO2 well enough to not have rapid bleed down. Andy.