Originally Posted by
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
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.