(a) Motorcycles must be grouped into classes determined by separate combinations of the following parameters:
(1) Engine type:
(i) Gasoline - two stroke.
(ii) Gasoline - four stroke.
(iii) Gasoline - rotary.
(iv) Other.
(2) Engine displacement.
(3) Engine configuration:
(i) Number of cylinders.
(ii) Cylinder arrangement (i.e., in line, opposed, etc.).
(4) Exhaust system:
(i) Muffler:
(A) Type,
(B) Location,
(C) Number.
(ii) Expansion chambers:
(A) Location,
(B) Size.
(iii) Spark arrestors.
(iv) Other exhaust system components.