125cc standing for 125 cubic centimeters, is a popular engine size, particularly of dirt bikes. For years, it was a very popular class in the AMA Supercross Series. It was generally considered the class below the 250cc class. Recently, 250cc four-strokes have been allowed in the 125cc class. Because of the increased engine size allowance, two-stroke 125cc engines have become nearly extinct in professional races. The series has been renamed the Supercross Lites Series, since 125cc engines are no longer used exclusively.

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