A valve stem is a device that allows you to put air in your tires Made of cast rubber, the valve stem has a spring-loaded valve that screws inside of it The air pressure within the tire forces the valve seat against a seal; this is how the air is held in a tire The valve snuggly fits into a hole in the rim that is smaller than its diameter; this forms an air seal Valve stems are subject to the weather and other environmental elements, causing the rubber to break down and leak Have them inspected every time you have your tires rotated (every 6,000 miles) and replace them every time you replace your tires
The point on a tire where it is filled with air When contact is made between cars, this stem is often sheered off by the other car's sheet metal Nascar rules require all tires to have two air chambers within a tire, so all tires have two valve stems The second stem is located deep in the rim, to protect it from being sheered off