SECTION 7.2

The maximum operating speed (max RPM) is marked on each wheel, its blotter, or (for small wheels) its container. This number and the outer diameter (D1, in inches) of the new wheel establishes its maximum surface feet per minute (max sfpm) by the following formula:

max sfpm = (p * D1 * max RPM) / 12

This formula allows the max sfpm of the new wheel to set the safe usage limit of the wheel. That is, as the wheel OD is worn down, its RPM may be increased as long as that max sfpm is never exceeded. To maintain the new-wheel sfpm as the OD wears, the following formula may be used:

max RPM 2 = D1 / (D2 * max RPM 1)