A positioning device includes a sleeve member engaged with one of holes defined in the wheel rim and a base has its shank extending through a passage of the sleeve member. A threaded hole is defined in the shank so that an end of a spoke is threadedly engaged with the threaded hole in the shank. A sealing ring made of non-metallic material is mounted to the sleeve member so as to seal the hole in the rim. The coating of the rim is not scrubbed by any of the parts of the positioning device and the installing processes are easy and can be finished within a short period of time.