An inflation system for tubeless bicycle tires may include a valve, a sealant canister, a pump head, and/or a valve core adapter. The valve, sealant canister, and pump head may collectively facilitate sealant injection into a tire by a user. The valve has an external valve seat, and includes a valve body, a valve stem extending through the length of the valve body, and a retaining mechanism for the valve stem disposed interior to the valve body. The valve stem is configured to move relative to the valve body, such that a resilient seating surface disposed at a proximal end of the valve stem is displaced relative to a valve seat formed by an exterior surface of a proximal end of the valve body.