The Honda CRF series is a line of four-stroke motocross, trail, and dual sport motorcycles manufactured and marketed by Honda. The CRF line was launched in 2000 as a successor to the Honda CR series. The full sized motocross bikes are equipped with liquid-cooled, single cylinder four-stroke engines that are available from to . They now have dual-sport motorcycles. The more trail friendly CRF's have simple air-cooled engines, and are available from to . The Honda CRF450R was the first in the series, followed by the CRF250R in 2004. Further down the line, the CRF450X and CRF250X bikes emerged, both designed for mostly off-road use. They are considered among the best motorcross bikes of their class, and have been a leading seller since their introduction. The CRF450R was CycleWorld's Best Motocrosser for a record eight consecutive years from 2002-2009. Engine technology The engines in these bikes use an over-square design, which means that the diameter of the cylinder is larger than the stroke of the piston. This allows for higher engine speeds and a reduction of reciprocating mass for a given displacement. Another technology that is used is short piston skirts. The "skirt" area of the piston is the portion on the side of the piston which comes into contact with the cylinder wall and aids piston stability. While the introduction of the shorter skirt on the piston helps to reduce reciprocating mass, it also leads to more "rocking" of the piston, or minute unwanted rotation of the piston around the axis of its wrist pin. This leads to more frequent maintenance intervals for the pistons, piston rings, and cylinder walls. Model overview CRF-F As of 2021, the CRF-F series includes the CRF50F, CRF110F, CRF125F, CRF125F (Big Wheel), CRF230F and CRF250F. For the 2019 Model year the CRF 110F, CRF125F, and CRF250F all come standard with electronic fuel injection. This improves cold weather starting and makes the bike easier to maintain because of the lack of a carburetor to clean. Simple, air-cooled 4-stroke motorcycles. Typically, these bikes come in low-power and confidence inspiring configurations for new market entrants. In all, Honda has made a CRF50F, CRF70F, CRF80F, CRF100F, CRF110F, CRF125F, CRF125FB, CRF150F, CRF230F, and a CRF250F. The CRF70F, CRF80F, CRF100F, CRF150F and the CRF230F have been discontinued. The 70 was replaced by the 110, the 80 and 100 were replaced by the 125, and the 150F does not have a