cyclezealot

This is like my second or third time I've had a flat adjacent to the valve stem . Upon removal I've discovered the tube folded over multiple times at the stem. Being that the tube and tire are 700 mm, how can ther4 be that much excess length.
. I insert the tube very carefully, the best one can see the tube is not crumpled upon insertion. To assure its not crumpled upon insertion , I partially inflate the tube prior to mounting the tire about the rim. . Deflate and insert the deflated tire on the rim. Several hundred miles later I have a flat, with the leak in the crumpled segment adjacent the valve stem. Anyone else have this problem. This seems so unnecessary and getting old. What am I doing wrong. Thanks.

79pmooney

Do you inflate them a little first? I always do. There's a simple way that requires neither a pump or air canister. Blow them up like a balloon. With your breath. A hard exhale by a cyclist gets just about exactly the right amount of air to get the tube to keep its shape but not resist the final mounting efforts.

Troul 

what are the specs of the wheel, tube, & tire? it might be undersized & upon rupturing, it pretzels in the tire cavity.

Andrew R Stewart 

Riding a tire under inflated will often result in the tire trying to shift rotationally around the wheel. The tube, however, is trapped in place by that pesky valve. So the tire shifts around dragging the tube with it and the tube bunches up on one side of the valve and is stretched out on the other side. Very often the valve becomes canted in the rim as it' base is being pulled one way and pushed from the other way. Andy

Trakhak

You say you partly inflate the tube to make sure that it doesn't fold when you insert it in the tire, and then fully deflate the tube.

I think that that last step is the problem.

I also always partly (minimally) inflate the tube and insert it into the tire. But, instead of immediately deflating the tube once it's in the tire, I leave the tube partly inflated and push the tire over the lip of the rim, all the way around one side of the wheel. Or if the tire is too tight on my first attempt, I let a tiny bit of air out of the tube and try again.

Once I have one side of the tire installed in the rim, I check to make sure that the stem is straight. If it isn't, I let a tiny bit of air out and pull the installed side of the tire along the rim until the stem straightens. If it seems appropriate to do so, I might reinflate the tube a bit, to make certain that it doesn't fold.

Finally, I begin seating the tire on the other side of the rim, working it on with both hands symmetrically away from the valve (after having first pushed the valve down into the tire to make sure that the reinforced valve seat doesn't prevent the tire from properly seating at the valve).

It isn't until I get to the point where the tire refuses to be pushed over the rim that I let most (or, if absolutely necessary, all) of the air out of the tube.

Having succeeded in getting both sides of the tire fully into the rim, I then inflate the tire to 10 pounds of pressure or so and check the tire's witness line all the way around the wheel to make sure that the tire is fully and evenly seated.

Once the tire is correctly seated, I inflate to about half of full pressure, check the tire seating again, and then, if the tire looks good, inflate to full pressure.

cyclezealot

This ocurred to me just after creating this post. You raise a good point. I have four bikes , I better be sure I have the right size tube for the correct tire. . Nah. I just checked. The tire was 25 mm and the tube was 18-25 mm.
. The above might be the real problem. I fully deflate the tube just prior to putting the tire on the rim.

rickpaulos

I see this all the time on newly donated bikes at our local bike coop. Mostly on juvenile bikes but it happens on all wheel sizes. If the valve stem is crooked at all, you can bet the tube is jammed up by the valve. Many bikes come in with the rim strips broken and hanging out. Turns out the Asian made rubber strips rot when exposed to air/sun and left out for a few years.

Next time you install the tire & tube, line the tire label up exactly at the valve stem or put some witness marks on the tire and rim with a sharpie. If the marks move apart, that is the evidence the tire is creeping around the rim.

You might think the air pressure will hold the tires in place. Generally true but not at low pressures. Old dry tires will slide easier. Stray talc on the rims make them slippery. Hard braking will want to move the tire.

In some motor sports, they drill holes through the rim and tire and bolt the tire to the rim to keep it from slipping. Drag cars with crazy amounts of torque and beach buggies with very low air pressures.

A small amount of glue (rubber cement) may help keep the tire from slipping.

Troul 

I'd try using a tube from the same brand that supports the next range up in tire width [25-32mm] .

KerryIrons

Perfect summation of the likely cause.

masonv45

I had this happening on my tubed MTB rims because the pressure is so low. Used cornstarch to make them "slippery" and it's never happened again.
Interestingly, it only happened on my disc brake MTB, not the rim brake MTB ... hmmm... :-)

grumpus

That's why I don't use lock rings on Presta valve stems - if the tube starts to migrate the stem indicates that by tilting, before any damage occurs. Not so useful with deep section rims, which will hold the stem straight.