Bicycle Mechanics - Valve stem explodes

OK, so maybe the thread title is a little dramatic. Just amusing myself mid-week.

My friend and I went on a ride this morning, and on the way back his back tire lost all of its air. We both heard it -- snap, hiss... flat. (Almost that quickly, too)

Of course the first thought was a nail or other debris, but examination revealed that the side of the valve stem (Schrader) was cut. My first guess is that the stem was rubbing against the hole in the rim, but we did ride for several miles before that. Maybe it just took that long to rub through.

Does this sound plausible? I didn't have time to do a thorough examination of the rim itself, since we were already running late. But I'm just wondering if it's common.

We've been riding almost every week, so I'm kind of surprised it didn't happen sooner if this is actually the cause. My friend hasn't done anything like removing the tire or tube from the bike, but he did pump up the tire with a small hand pump before the ride this morning (so perhaps he wasn't careful enough and cut the stem against the edge of the hole in the rim).

If my friend was the one to cut the stem accidentally, would there be any prevention to this thing aside from just thwapping him upside the head and telling him to be more careful? Maybe convincing him to switch to Presta?

Also, aside from carrying a spare tube (which I'm seriously considering anyway), is there any way to repair this long enough to get home?

yes this is common, i take it he was riding on low pressure,and the tube move inside the tire when he was braking ? the best way to deal with this is to keep them up to pressure. ( and check for any burr around the hole in the rim).

Of course the first thought was a nail or other debris, but examination revealed that the side of the valve stem (Schrader) was cut. My first guess is that the stem was rubbing against the hole in the rim, but we did ride for several miles before that. Maybe it just took that long to rub through.

Does this sound plausible? I didn't have time to do a thorough examination of the rim itself, since we were already running late. But I'm just wondering if it's common.

Yup. Very common. It's the main weakness with Scrader valves. Presta doesn't have the same weakness, either.


We've been riding almost every week, so I'm kind of surprised it didn't happen sooner if this is actually the cause. My friend hasn't done anything like removing the tire or tube from the bike, but he did pump up the tire with a small hand pump before the ride this morning (so perhaps he wasn't careful enough and cut the stem against the edge of the hole in the rim).

If my friend was the one to cut the stem accidentally, would there be any prevention to this thing aside from just thwapping him upside the head and telling him to be more careful? Maybe convincing him to switch to Presta?

Also, aside from carrying a spare tube (which I'm seriously considering anyway), is there any way to repair this long enough to get home?

Pumping by hand will wiggle the valve around in the rim and can lead to cuts on the stem. Low tire pressure can also allow the tube to move in the tire and end up cutting the stem. Deburring the valve stem hole can help avoid this or going to presta. Also a better pump, like the Topeak Morph, helps.

You should always carry a tube and a patch kit but it's unlikely you can repair this kind of leak. Kinda kills the tube.

I have both a tube and patch kit for my trike, but the 16 inch tubes are not something that would fit his 700x35C wheels. I should have been clearer in earlier post -- I'm considering carrying a tube that would fit his bike (he still doesn't have a patch kit, just hasn't gotten around to it, and I have space in the bag on my rack, and it's not like a tube is a huge investment).

I don't think he was riding on low pressure, since he had just pumped up the tire before the ride. So the hand pumping is probably what did it. Just seemed odd to me that we rode for quite a while before it went flat.

Oh, and I also forgot to mention that we did attempt to patch the stem, but it didn't hold even for pumping up the tire again. I've patched my tubes several times, but the patch didn't wrap around the stem very well, so it didn't surprise me that the patch didn't hold.

I have both a tube and patch kit for my trike, but the 16 inch tubes are not something that would fit his 700x35C wheels. I should have been clearer in earlier post -- I'm considering carrying a tube that would fit his bike (he still doesn't have a patch kit, just hasn't gotten around to it, and I have space in the bag on my rack, and it's not like a tube is a huge investment).

I don't think he was riding on low pressure, since he had just pumped up the tire before the ride. So the hand pumping is probably what did it. Just seemed odd to me that we rode for quite a while before it went flat.

Oh, and I also forgot to mention that we did attempt to patch the stem, but it didn't hold even for pumping up the tire again. I've patched my tubes several times, but the patch didn't wrap around the stem very well, so it didn't surprise me that the patch didn't hold.

Make him carry his own damned junk;) If he forgets, I find that long walks often improve my memory:D

I don't doubt that the patch didn't hold on the stem. I've never heard of anyone being able to salvage that kind of cut.

I have had the valve explode from high pressure, but just once.

Make him carry his own damned junk;) If he forgets, I find that long walks often improve my memory:D
The only reason I didn't discard the thought immediately is because the Trek I have uses the same size tires.

But you're right. I'll make him walk next time.

I don't doubt that the patch didn't hold on the stem. I've never heard of anyone being able to salvage that kind of cut.
It was worth a shot, in my opinion, even if I didn't have high hopes for the success. Just think of the glory and fame I'd have if I had succeeded! I'm sure that the parades and money and my picture on the cover of magazines would be well worth the price of a patch.

...can you tell it's getting to be that time of day when heading home sounds good?

I have had the valve explode from high pressure, but just once.
This definitely wasn't a high pressure scenario. I think we're looking at 50 psi or so. If that.