What keeps a tire securely on the rim?

The tire bead is the correct answer because it plays a critical role in keeping the tire securely mounted on the rim. The tire bead is a continuous, thick rubber band that runs along the inner edge of the tire. It is designed to fit snugly against the rim's edges, creating a seal that holds the tire in place, especially when inflated. The fit between the tire bead and the rim is essential for maintaining the tire's structure and ensuring that it does not slip off, which can lead to flats or blowouts.

Air pressure is important for the overall performance and functionality of the tire, as it helps maintain the tire's shape and facilitates contact with the road surface. However, it is the tire bead's physical structure and grip on the rim that actually secures the tire in position. While rim locks can offer additional security in certain applications, they are not standard in all tire designs and primarily serve specialized purposes. The tire valve, meanwhile, is responsible for inflating and deflating the tire but does not contribute to keeping the tire on the rim. Therefore, the tire bead is the key component in ensuring that the tire remains securely attached to the rim during use.