The power of compressed air

[sjbraun]

So, if you're ever tempted to use an inner tube marked 18-25mm in a 40mm tire, I recommend you don't. Here's what happens to your rim when the tube explodes. I managed to make a boot out of the blown tube and road home without any further problems. When I got home and removed the rim tape, I was surprised to see the extent of the damage. Looks like I'll be heading to Fairwheel Bikes for a rim replacement.

[ultraman6970]

stuff like that never happens with tubulars :P

[rnhood]

I doubt it ever happens with good rims either.

[sjbraun]

It was a good rim, Pacenti SL 23, version 1.

[Birddog]

I can't see how that happened. How much pressure did you have in the tire?

[soulspinner]

I doubt it ever happens with good rims either.

I thought Pacentis were good rims...:confused:

[thirdgenbird]

I don't think this has anything to do with the inner tube and tire combo. PSI is PSI. Sure a smaller tube will be thinner when expended, but a blowout with the "proper" tube would still be 90psi or whatever you were running. The rim and tire are what determines volume and pressure.

[cinema]

have you ever blown up any size tube outside of a tire? they get giant. i have run 23-28mm tubes in 29er tires. In my own experience that does not look like it is due to the size of the tube

[PaulE]

have you ever blown up any size tube outside of a tire? they get giant. i have run 23-28mm tubes in 29er tires. In my own experience that does not look like it is due to the size of the tube

I save up tubes with holes and patch them all at once sometimes. So I blow up the tubes to find the leak. Sometimes there is the mystery leak - you can' find the hole but if you leave the tube blown up overnight the next day it is flat again. One time I had a tube with the mystery leak and I got carried away blowing it up. After the tube got really big, it did pop with a loud bang.

When I was a kid I once filled up a 27x1-1/8 tire with a Schraeder valve using a gas station's air hose which had no pressure regulator. I put so much air in the tire the tube pushed the wire bead of the tire off of the rim and then the tube had a big bubble protruding out between the bead and the rim. Before I could relieve any of the pressure at the valve stem, the tube then burst. But the rim and tire were both undamaged and lived on for a long time with a new tube put in and pumped up by hand.

My experience in these matters is limited, but I think that something other than the size of the tube you used was also a significant factor in this event. Why don't you ask Kirk Pacenti what he thinks?

[Satellite]

Nothing to add but, "Wow" that is crazy!

[Black Dog]

100% not a tube size issue. Man, how much pressure were you running? 200psi, 300psi...??? :eek: Seriously, did the tube fail at the valve? That might explain the rim damage as that is the only place for the air to get out of the system.

[mg2ride]

Nothing to add but, "Wow" that is crazy!

+1

I would be interested if that could ever be duplicated. It does not make any sense to me.

[Joxster]

Conti test they're tubes to 500psi with the tyres. On the Tubs they go to 850psi before the rim collapses. I suspect you've been unlucky

[parris]

It looks like something got hold of the valve stem and ripped it out at an angle.:)

[parris]

Sorry no smiley intended hit the wrong button.

[Peter P.]

I read somewhere that typical tires are tested to withstand double the maximum inflation pressure. I would assume the tire would fail before the rim. I'm inclined to think something else caused the rim damage but an exploding tube/tire would not be my first conclusion.

[R3awak3n]

@ parris you can edit your posts btw :)

[AngryScientist]

smile you son of a....

http://3.bp.blogspot.com/-5BWGlqCJV7c/VVTv4o67D1I/AAAAAAAAkbg/gr6yAtrylDY/s1600/37..png

[Satellite]

smile you son of a...

Wow that takes me way back and still scares the living BEJESUS out of me. I was an impressionable kid when JAWS came out. The only movie that scared me more was Holloween with Mike Meyers.

[Mark McM]

I agree with the others - the "exploding tube" did not cause the rim damage.

The tube is not what holds the pressure - the tire casing is what holds the pressure. The inner tube is just there to keep the air from leaking out any pores or holes in cavity inside the tire & rim. When a tube bursts, it actually decreases the forces on the tire/rim due to the loss of pressure.

Looking at the second photo, it looks like the damage to the valve hole in the rim bed is on the opposite side of the as deformation of the external valve hole. That would imply that something grabbed the valve (while the wheel was spinning) and generated a bending force on the valve stem. This in turn would cause damage to the valve holes on opposite sides as the valve was bent backward. Any force strong enough to damage the rim like that would likely also have broken the valve stem off the tube, which is probably what caused the tube "explosion".

[pdmtong]

I save up tubes with holes and patch them all at once sometimes. So I blow up the tubes to find the leak. Sometimes there is the mystery leak - you can' find the hole but if you leave the tube blown up overnight the next day it is flat again.
inflate the tube and stick a part of it in a bucket of water. I use a painters bucket from home depot. keep rotating the tube through the water - you will see bubbles where the leak is.

[sjbraun]

The valve stem was not blown off the tube. The tube was split on the seam adjacent to the stem. To me, it looks like the force went from the inside of the rim then out through the outside of the rim. I can't see any other explanation than the force of the exploding tube deformed the rim, from inside to outside. I'm curious to see what Kurt Pacenti thinks.


I agree with the others - the "exploding tube" did not cause the rim damage.

The tube is not what holds the pressure - the tire casing is what holds the pressure. The inner tube is just there to keep the air from leaking out any pores or holes in cavity inside the tire & rim. When a tube bursts, it actually decreases the forces on the tire/rim due to the loss of pressure.

Looking at the second photo, it looks like the damage to the valve hole in the rim bed is on the opposite side of the as deformation of the external valve hole. That would imply that something grabbed the valve (while the wheel was spinning) and generated a bending force on the valve stem. This in turn would cause damage to the valve holes on opposite sides as the valve was bent backward. Any force strong enough to damage the rim like that would likely also have broken the valve stem off the tube, which is probably what caused the tube "explosion".

[blakcloud]

I wouldn't have thought that damage was even possible with a tube and tire. Looking forward to what KP says.

[Hindmost]

Using this wheel, was the bike ever hung from a hook or strapped to a roof rack?

[jc031699]

If the tire somehow slid circumferentially along the rim, taking the tube with it while the valve stayed anchored to the valve hole, it could have done something like this. The tube rupturing would have allowed the tire to slide. Sudden hard braking or acceleration just at the time of rupture would be needed to spin the tire relative to the wheel.

[oldpotatoe]

If the tire somehow slid circumferentially along the rim, taking the tube with it while the valve stayed anchored to the valve hole, it could have done something like this. The tube rupturing would have allowed the tire to slide. Sudden hard braking or acceleration just at the time of rupture would be needed to spin the tire relative to the wheel.

Why ya powder yer tubes....

[Chief]

If the tube was rated 18-25 mm, then it had a diameter less than 18 mm otherwise the tube would wrinkle when placed in a 18 mm rim. So let's assume that the tube diameter is 18 mm so that we may attach some numbers to the event because as Einstein said if you can't attach a number to it, you have nothing. When placed in a 40 mm diameter tire and inflated, tube's radius would increase 11 mm = (40 -18)/2 : i.e., more than double. If the inflated tube ruptured, the tube would want to recover its initial radius, diameter or cross section circumference; i.e. its initial shape. If there was no retaining nut on the stem, then the stem would retract at least 11 mm, difference in tube's inflated and uninflated radii. That is at least 11 mm of the stem would be pulled into the rim from the blow out. The load on the rotating wheel would want to flatten the stem and likely produce the damage seen on the inside as well as on the outside of the rim. While the blow out may have precipitated the damage, the pressure release acting alone did not produce the damage.

[Mark McM]

The valve stem was not blown off the tube. The tube was split on the seam adjacent to the stem. To me, it looks like the force went from the inside of the rim then out through the outside of the rim. I can't see any other explanation than the force of the exploding tube deformed the rim, from inside to outside. I'm curious to see what Kurt Pacenti thinks.

Your scenario is impossible. If the tube is completely inside an intact tire/rim, than the tube is not holding the pressure - the tire and rim are the structural elements holding the pressure. Therefore, since the tube is not holding back the pressure, it can not release the pressure in an explosion when it is inside the tire/rim.

The description of the damage to the tube is very telling. As noted, when the tube is inside the tire/rim, it can not explode. However, if the bead lifts off the rim and exposes the tube to the outside, the tube at that point is being asked to hold the internal pressure. As tubes are not nearly strong enough to hold high pressure, they will almost immediately explode. And as the gap between the tire and rim is a typically a long, narrow slit, the hole in the blown tube tends to be a long slit as well.

With this additional information, it seems likely that the damage to the rim occurred after the tire lifted off the rim and the tube exploded. With the tire deflated and not completely seated on the rim, the tire/tube can shift around the circumference, causing the stem to cock in the valve hole, resulting in the damage seen around the valve hole.

So the question is, how did the tire lift off the rim? The most common cause is tube installation error. Sometimes a small portion of the tube gets trapped between the tire and rim. Over time, air from inside the main tube chamber can leak into the herniated section of the tube. When enough pressure has built up in the herniated section, it can lift the tire off the rim in that section, exposing the tube to the outside, resulting in a loud Bang and the long tear in the tube you described.