[tigris99]

Was out riding with my son on new/in progress built trails im helping build. First time there. As any would know new trails are a bit rough. He was on a trek mt60 with new xr1 "comp" 20" tires.

Ride was fine till very large root (looked more like half buried tree lol) which I went over no issue then son followed behind. His rear slid (its off camber on top of being rather large) and bounced causing him to fall over just after clearing it.

We went to take off again and he hollars his rear tire is making a funny noise, the way he described it said "flat" to me, had him check, it was.....

Ok so trail side tire repair, no buggy, good time to teach him. Except couldn't find a puncture anywhere. Wasn't about to waste a CO2 for no reason. Luckily that root was right near park paved paths and short walk back to trailhead.

Got back to car, took everything apart and inspected closely, not only no puncture but tube was holding some pressure, what remained after initial loss I guess. Inspected tire insanely close, nothing, squeezed the tube and ever thing, no more air loss.....WTF????

His mom calls saying I need to bring him home, so we load up, I drop him off and come home. Spent 20mins inspecting things again in the garage, nothing, so air up tube alone unmounted. No leaks!!!! Even checked with soapy water. WTF IS GOING ON????

Tube is older and just tried to take valve core out (Schrader) and can't, its bent or something, off to one side inside the stem can't get tool in.

Could the impact and bounce have jarred the stem that much??? Did we walk out for nothing when I have co2s I carry on me??? And would adapting his wheels to presta (if I can find 20" presta tubes that aren't way overpriced) avoid a repeat of this?



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[J.B. Weld]

Small leaks can be tough to find, I drastically over inflate the tube to about double it's normal width and immerse it in water.

 

[Guest]

I'd be inclined to blame the valve core. If the tube is older (more than a couple years) I'd toss it and start clean. You'll have a hard time finding presta tubes in any 20" widths wide enough for your son's bike. The Presta valved 20" tubes all seem to be in the 1" to 1.5" range.

 

[gmats]

This is a WAG - Wild A$s Guess. Was there a valve cap on or no valve cap?

Is it possible when he fell, the stick or something hit the valve stem and just happen to push the valve core in there by letting air out. I know it is extremely far fetched but seems to give the an explanation why you can't find a "leak". You can't get the valve core out? Is it because the schrader valve is bent? I cannot imagine why presta would be better. This could have just been a freak of nature. The way I see it, only ways for air to get out of a tube would be the valve (core, stem, broken stem) or tube itself. If he heard air, it was rushing out and not just simple slow leak.

Tubes are cheap in this case, check the tire and put a new one in and I think you'll be OK. Yes, freaky!!

 

[Kronk]

Possible that there is a cut around the base of the valve stem. Holds air unless the stem has pressure pushing on it.
I have had a tire go flat while stopped, aired it back up to see if I could hear the leak. Held air for another 30 minutes, then flatted in seconds. Was the valve stem having been cut by the rim from the rim strip slipping out of place.

 

[MTBMILES]

Possible that there is a cut around the base of the valve stem. Holds air unless the stem has pressure pushing on it.
I have had a tire go flat while stopped, aired it back up to see if I could hear the leak. Held air for another 30 minutes, then flatted in seconds. Was the valve stem having been cut by the rim from the rim strip slipping out of place.

I have had this happen too.

 

[BrentD]

I have had this happen too.

Thirded. Sounds like the problem to me.

 

[tigris99]

It had a cap on it. It did go flat over the last 24hrs. Just never been stumped like this lol. Especially with not any evidence on the tire and a stem cap on.

Being it seems to be just a random occurrence on an old tube ill just order a pair of new ones, keep the good old one for a spare.

Thnx for the help, thought I was loosing my mind but in this case im not at least.

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[Guest]

Reminds me of the guy at work who's front tire keeps flatting for no reason (a small leak but nothing in the tire). Then he mentions that the last flat was on the inside of the tube. One of life's great mysteries is why companies use crap rim tape or too narrow rim tape. So we pull his tire off and I wrap the rim with two layers of duct tape (to get him home) and viola! no more flats. He asked last week how long I thought the tape would last and I said "Not really sure, I built a set of touring wheels in 1981 with duct tape and they still work so I guess you're good for the time being."