dress the periphery of all new rubber wheel and make concentric to the bore of the steel disk upon which the rubber is mounted. The concentricity of the rim shall be within .05 mm (.002 in.) total indicator reading on the diameter. Follow the same dressing procedure on used wheel that develop grooves or that wear unevenly so as to develop trapezoidal or unevenly wear scars on the test specimen (fig. 11). The intent is to produce a uniform surface that will run tangent to to the test specimen without causing vibration or hopping of the lever arm. The wear scars shall be rectangular in shape and of uniform depth at any section across the width. The rubber wheel may be used until the diameter wears to 315.9 mm (8.50 in.). New rubber rims may be mounted on steel disk by the qualified source.