Okay -- this morning I left the house for my multi-mode commute, and as I rolled the bike out to the car, I noted that my rear tire was flat. I had ridden yesterday, so it seemed odd, but I was late, so I decided I'd fix it at my 'mid' point.

I checked the tire and rim for sharps/burrs/thorns, etc... found nothing. I found the hole in the tube, patched it, re-mounted and tried re-inflating. This resulted in another flat, though I thought I might have missed the actual hole in my haste. I re-patched the tube, remounted, and all seemed well enough... a mile later, I was flat again. I re-checked everything, straightened out some sloppy spots on the rim tape, installed a new tube, and started again. Another mile/mile and a half, and another flat. I limped to the office by re-inflating and riding very gently.... I'm now in my office with the tire and wheel in hand, looking furiously for a thorn or something in the tire, or some sort of burr or sharp on the wheel, but nothing.

What am I missing?

Air the tube and place sections under water in a sink and look for tiny bubbles.

Glass and radial tire wires can hide in the tire.

Turn the tire inside out and look again.

Thanks for the speedy reply. I should have mentioned that I had the tire inside out and ride side out while looking for sharps. I'm looking again, though. In case anyone things it matters, the tires are folding bead, panaracer T-Serv PT tires...

I studied the holes more closely on both tubes, and the holes are all on the 'inside' where the tube is more likely to be in contact with the rim. I'm taking a more careful look at the rim tape and the inside of the rim now, too.

Grrr!

Cool....

"I'm taking a more careful look at the rim tape and the inside of the rim now"

Its your rim tape. If it is stock rim tape that came with the bike, it sucks. Been there many times!

In your hurry you squeezed the tube between the tire bead and the rim while mounting the tire back on the wheel. It happened to me last spring (same scenario) . Now I take my time when mounting the tire and I make sure that the tube is placed properly before I inflate it.

I just discovered the wonders of radial tire wires. Could not find a problem with the tire, which is a Gator Skin and thought I might have a burr in the rim. I had a bunch flats over a short period of time. I took it to a shop to look at the rim and the mechanic found a wire in the tire I had not found.

Tiny Wire:
https://i256.photobucket.com/albums/h...s/Royswire.jpg

Booo!!!!!!

I agree with Chef that you should consider this possibility - if you have the crappy thin rubber rim tape that came with the bike, replace it with cloth tape ($2 at your LBS). The only two flats I have had (front and back, same day) were due to my 100 psi tubes finally pushing through the thin rubber rim tape that came with the bike and puncturing themselves on the sharp spoke ends.

File them flush... it's a free solution and preventative measure.

And that is what it looked like.

I think the answer was a tiny wire

My first response, take a piece of cloth, not paper towel, not silk, but even a shop towel, better cheesecloth or something similarly soft and run it around the rim and tire, actually, "bike shop lesson 101, long before patching, find the cause", not to be rude, just common sense, err, not having the proper tool is disastrous, err, the proper tool would have been a cotton towel to find the culprit.

velox fond de jante

That isn't much smaller than the wire they got me about a week ago :-(

I use a cotton ball. It'll snag on things you can feel, and leave strings to show you where it got caught. Cheap, light, works great. In a pinch, on the side of the road, you could use a pulled apart cigarette filter. Sadly, not hard to find a butt most places.

I always just find a way to submerge part of the tire in a pan of water and look for small bubbles... while it might not be possible on the road, it saves time if it's one of those small leaks that are hard to find.

for double walled rims
Generally, it is not spoke ends that cause the puncture, nor does the edge of the spoke hole cut the tube.
The 'puncture' results from the inner tube stretching too thin/too far in a highly localized area. Inner tubes act as a seal to keep air in, but do not actually resist pressure on their own; the tire and rim are what contains the air into a pressurized space. With a double walled rim, the holes on the inner wall do not support the tube thus it expands into the opening till it pops. Same concept as when you get a sidewall tear and the tube bubbles out like a pimple...

cloth tape is needed on double wall rims to bridge the spoke holes and keep the tube contained.
rubber strips are stretchy and will eventually get pushed through

single walled rims are a different story; spoke ends really do intrude into the inner tube's living space. rubber strips are good here since they are thicker than cloth and will smooth over the produding spoke nipples better...

Often the people who spec bikes for mass market are not actual mechanics or cyclists and dont realize the distinction other than the rubber rim strip is cheaper than the cloth one. So new bikes often have the wrong thing.... works ok on the display rack; not so once fully pressured and actually ridden a month or so...

Thanks to all who replied. I thought I had it solved yesterday, after re-installing the rim tape more carefully, as the tire held air for my entire ride yesterday afternoon. However, this morning, my tire was flat again, and it definitely has a slow leak. How slow? Well, I've re-inflated it here at work to a full 97 PSI and it has no apparent leakage. It's been 3-4 hours, and the tire remains fully inflated (as determined by the gauge on my pump). I'm guessing that a tire wire or similar tiny sharp is my likely culprit, and I'll need to spend some real time at home finding it, using the methods described. Of course, the one issue that seems to speak against this is that the holes have been more toward the 'rim' side of the tube... not right against the holes, but definitely well inside the bead of the tire, I think...

Rim tape: Cloth rim tape is what is installed, but whoever at my LBS installed it did a crap job, as it was really crooked and not covering the entire circumference of all of the holes. Having said that, it does not appear that it is the cause, as I repositioned it very carefully, and further, the holes I found in the tubes were tiny pin holes, and there was no 'stretch' or 'strain' on the rubber of the tube around the offended area. I'm not ruling it out, but it seems less likely?

Pinched tube: While that might have been true of one of my attempts, I was pretty careful in the subsequent attempts. Also, that usually shows, in the form of some kind of irregularity on the rubber where it stretched or tore. These are tiny pin-holes in the tube with no apparent scuffing or straining of the rubber.

I'll update when I finally solve this! Thanks again to all.

I read through rather quickly, have you determined that the hole in the tube is on the inner (rim) side, or on the outer (rolling) side? Someone mentioned using a cotton ball, this is my favorite trick for something that's embedded in the tire but that you can't see. A cotton ball will snag and leave a trail of cotton right back to the culprit. If it's on the inside, I would entirely remove any and all rim tape and re-install new tape carefully and evenly. There are many youtube videos on how to do this correctly. Part of doing it correctly is dependent on having the correct width of tape. It should fit from rim sidewall to rim sidewall with no gaps. It is worth trying the cotton ball trick on the rim as well. If there is a little burr that is causing your issues, again the cotton will snag on the offending burr.

If the tube doesn't seem to have a hole, the next thing I'd check is the valve core. If it's dirty, or not entirely screwed in (if it's a removeable core) then air will slowly seep out of the valve.

Cotton balls! Definitely cotton balls.

Good explanation, thanks. I have double-walled rims, so what I experienced was the tube pushing thru the rubber strip and into the spoke hole space and popping. My former LBS guy described it to me mostly correctly, but said it was the spoke ends that it pushed in to. Expanding into the opening until it pops due to localized pressure makes more sense - thanks for helping me understand that better. Switching to cloth has solved the problem for my double-wall rims.

Had a similar situation once. Turned out to be a sharp rock that was only exposed when the tire was inflated, likely picked up on the Towpath. When inspecting the tire with my finger and cotton ball, there was nothing. I saw a tiny little disturbed area on the inside, and pushed a nail through there. Lo and behold, there was a good size rock embedded in the casing. As we both ride in the same area, this could your issue, as well.

Make sure you line up the valve stem of the tube with the brand logo (or other identifiable unique spot) of the tire when you do your repairs. Then when you find the hole in your tube, it's easy to line it up to a spot on either the rim or the tire. Makes diagnosing flats infinitely easier. I've found a few things this way that I might have missed other ways.

If you already do this, then let this serve as general advice to others who might find it helpful.