If there’s difficulty balancing a tire and the dynamic balancing machine is requiring more and more weights around the rim, suspect something may be inside the tire. It could be an emergency liquid flat repair, excessive compressor liquid, or something inside the tire causing this problem. The tire must be dismounted to verify this condition. Unbalanced tires cause a vibration that increases with vehicle speed. They also wear and become cupped.
Today's vehicles contain (TPMS) Tire Pressure Monitoring Systems. They may be direct or indirect. An indirect system uses wheel speed sensors to calculate tire pressure based on the principle that a tire with low air pressure will have a lower profile and spin faster that a properly inflated tire will. Today's direct TPMS systems contain a sensor located in each wheel, beware often including, and don’t forget to check, the spare. These sensors can become contaminated with liquid in the tire. They also become contaminated from the environment by simply leaving the protective cap of the sensor or replacing the special nickel valve core with a standard brass one. Always use the correct core. Some TPMS sensors have rubber valve stems instead of the standard metal stem found on many TPMS sensors.