An adjustable hub adapter for coupling an on-car brake lathe to a wheel hub. An annular support frame coaxially carries an axially bored and threaded central mounting hub with a set of equidistantly spaced spokes. A lug bolt receiver is associated with each spoke, and consists of a receiving tube, a lever arm pivotally coupled to the spoke at a pivot bolt in proximity to the annular support frame. An engagement pin on each lever arm is captured within a synchronizing ring carried on the annular support frame. The rotational movement of any lug bolt receiver about an axis of the pivot bolt imparts rotational movement to the synchronizing ring, and in turn, causes each remaining bolt receiver to rotate about an associated pivot bolt axis, maintaining the lug bolt receivers in a synchronized and symmetric radial displacement from the central mounting hub.