Dirt bikes in the 125-cubic-centimeter-engine category have top speeds that range from 55 to 60 miles per hour. Heavy riders and downhill road conditions can push the operating speed above this range although it is not recommended by dirt bike manufacturers to let this intentionally happen.
Dirt bikes with 125 cubic centimeter engines range from 5.9 to 7.8 horsepower at 7500 revolutions per minute. They tend to feature single cylinder, four-stroke engines. Four-stroke engines, the most common type of modern engine, have four distinct phases: intake, compression, power and exhaust. New dirt bikes in the 125-cubic-centimeter class range in price from $495 to $1,516, as of October 2014.