An archaic
car part that has been made mostly obsolete by tubeless tires. These days an inner tube is much more useful for floating on
water, or for sledding on snow. It's a lot more fun that way too.
It's
soft, inflated, donut-shaped, usually black, and frequently has patches glued to it where it had leaked.
Smaller versions may still be found in many bicycle tires.
I was shocked when I took that tire off the rim, and found an inner
tube inside it.
Watch out for the stem of that inner tube. If you
break that part, there's no patching it, and it can leave a nasty scratch on your
skin too.