A tire uniformity machine having a framework for receiving a tire to be tested, a rotatable chuck located within the framework and having a spindle driven by a motor directly coupled to the spindle to selectively cause rotation thereof, whereby the tire is chucked within the chuck assembly and caused to rotate by the motor. The TPU elastomers exhibit good optical clarity, particularly when formed into relatively thick injection molded parts. Locks are provided at the right and left ends of the extension pieces to lock the extension pieces to each other in the overlapped state. The perlite in the fixed bed is then replaced, with the exhausted perlite disposed of as appropriate. The side members preferably have a lower lip for supporting the fuel unit.