seat, recumbents are not as easy to use on tight, curving unpaved singletrack. Large-diameter wheels, mountain gearing and off-road specific design have been used since 1999. Crank-forward designs that facilitate climbing out of the saddle, such as the RANS Dynamik, also can be used off-road. Lowracers Lowracers are a type of recumbent more common in Europe among racing enthusiasts. These typically have two 20" wheels or a 26" wheel at the rear and 20" wheel at the front. The seat is positioned between the wheels rather than above them. The extreme reclined position, and the fact that the rider is sitting in line with the wheels rather than atop them, makes this type the most aerodynamic of unfaired recumbents. Highracers Highracers are distinguished by using two large wheels (usually ISO 559, 650c or 700c). This necessitates a higher bottom bracket than on a lowracer so that the rider's legs are above the front wheel, and this in turn requires a higher seat. The seating position may be otherwise identical to that on a lowracer allowing similar aerodynamics. "Racer" in the name implies that this will often be the case, since these bikes strive for speed. Highracers are generally more maneuverable than lowracers since their higher center of mass make them easier to balance at lower speeds. Given the same seating position they may be faster than lowracers, since it is widely believed that rolling resistance is inversely proportional to wheel diameter. However, lowracer proponents reply that their design is faster due to aerodynamics. The reasoning is that the riders body is in line with the wheels, reducing drag. Hip and elbow injuries are more common on highracers than on lowracers due to the greater height from which the rider can fall. However, the injuries are very rare and seldom serious. Semi-recumbent and crank forward bicycles Bicycles that use positions intermediate between a conventional upright and a recumbent are called semi-recumbent or crank forward designs. These generally are intended for casual use and have comfort and ease of use as primary objectives, with aerodynamics sacrificed for this purpose. Tandem recumbents Just as with upright bicycles, recumbents are built and marketed with more than one seat, thus combining the advantages of recumbents with those of tandem bicycles. In order to keep the wheelbase from being any longer than absolutely necessary, tandem recumbents often place the stoker's crankset under the captain's seat. A common configuration for two riders in the recumbent position is the sociable tandem, wherein the two riders ride side by side. There are also hybrid recumbent designs such as the Hase Pino Allround that utilize a recumbent stoker in the front, and an upright pilot in the rear. Recumbent tricycles Recumbent tricycles (trikes) are closely related to recumbent bicycles, but have three wheels instead of two. Handcycles In order to accommodate paraplegics and other individuals with little or no use of their legs, many manufacturers have designed and released hand-powered recumbent trikes, or handcycles. Handcycles are a regular sight at HPV meetings and are beginning to be seen on the streets. They usually follow a delta design with front wheels driven by standard dérailleur gearing powered by hand cranks. Brake levers are usually mounted on the hand holds, which are usually set with no offset rather than the 180° of pedal cranks. The entire crank assembly and the front wheel turn together, allowing the rider to steer and crank simultaneously. Although arms are weaker than legs, many hand cyclists are able to make use of the power of the whole upper body. A good hand cyclist can still achieve a