tyrion

Suppose you need to fix leak and can't find the puncture. You don't have access to water to submerge it in, so over inflating the tube would help find it (by hearing the "hiss" or feeling the air flow). How much do you dare over inflate the tube?

3x specified max size?

10 Wheels

2 x

xenologer

Until I hear the hissing or it blows up.
Either way the tube is already punctured, so no loss.

FBinNY 

2-3 times the unflated diameter. However, do this progressively because sometimes, though rarely, a cut can become the start of a tear, and the stress of being stretched can pull it apart.

BTW - this is why I carry a spare instead of a patch kit. Looking for leaks and patching them is something I prefer to do at my leisure.

2_i 

Right above the corners of mouth the face seems particularly sensitive to air flow.

tyrion

I carry a spare and a patch kit too, and have had that 2nd flat in one outing.

tyrion

Really? Never would have guessed that.

hueyhoolihan

nose hairs too. really.

if there's a lot of traffic, very noisy and have trouble hearing the hiss, i've resorted to this a couple of times with some success.

BTW, i've had them inflated to the size of a hula hoop (if that reference still has merit), in diameter, without a mishap.

HillRider

Which is why I carry two spare tubes and don't bother with the patch kit. I'd rather patch the tube at home where it's dry and comfortable and the little tube of glue in the road kit is inevitably dried out when I need it.

Sy Reene

I've always heard to just use your wet tongue.. very sensitive.. but you might look a bit suspect.

dksix

If I can't see the hole I'll hold the tube close to my face and rotate it around. I'll feel it on my face well enough to isolate the area and if I still can't find it them I'll spit on my finger and move over the area. I had one like this just yesterday. I took about 15 minutes from when I first felt the low tire for it to lose enough air for me to stop riding. Ended up having to push for about the last half mile or so back to where I had parked my truck. A single puncture from a single piece of wire from what I assume were an automotive steel belted radial. It was just barely sticking through the tire, had a hard time getting a hold of it with needle nosed pliers to pull it out.

Retro Grouch 

Whatever it takes.

If you have a leak you aren't going to want to use the tube as it is so what do you have to lose?

tyrion

The more you inflate it the easier it is to find the leak, so basically what I want to know is how easy can I make finding the leak without wrecking the tube.

FBinNY 

As was posted early on, 2-3x the unsurpassed width. Probably more is OK but, 2-x is safe.

Reynolds 

I've inflated tubes to the point a short section bulges to more than 3x without bursting.

Leisesturm

Do I detect a bit of snark there? I'm not sure why when people get bored and ask dumb questions to the open forum they get upset when they are treated like they are weak in the head. Seems fair. <shrug>

tyrion

No.

dabac

Good point.

Tube wall thickness isn't finely controlled. One needs to watch out for a section that might suddenly take off.

2_i 

Completely serious from my side. I thereafter scanned medical literature for sensitivity to airflow and there is nearly nothing there: a lot on basic skin senses, i.e. touch, pressure, temperature and pain and a bit on draft. Looks like a topic for a paper.

Leebo

Lick your lips, works well. ^^^^

pdlamb

I don't know if I hit FB's 2-3X, but when you're pumping up a tube it's kind of like blowing up a new balloon. For a while you get the tube firm, then, like the balloon, the diameter expands dramatically. Get that all the way around the tube and start dunking.

Leisesturm

medical literature? As a 15 year old fixing flats on my Huffy the older boys (not that much older either) were showing us how to find leaks and were holding the tubes to their faces. WebMD or The Journal of Neurological and Behavioral Science didn't inform their technique! Kids today need to get out more and do stuff together instead of playing massively multi-player video games on the Internet. I'm not blaming, or judging you personally. It's not your fault. But it is a fault.

Vintage_Cyclist

As previously mentioned:

1. Carry a spare tube AND a few patches/glue. While getting more than 1 flat in a ride is unusual, it happens (my personal record is 4).
2. Feeling for escaping air with your hand almost always works, but I have resorted to holding the tube against my face, which usually works. If you can't feel it (very rarely), then it's usually off to the bucket of water.
3. Another thing to keep in mind is the position of the tube on the tire. If I resort to patching a flat on the road, I leave the valve in the rim. This way, after finding the hole in the tube, I can lay the tube along the tire and pinpoint the cause. This method can also work in reverse, if you have trouble finding the hole, but can locate the cause in the tire.