Front suspension
Historically, with motorcycles borrowing so heavily from bicycle technology, the first front suspensions were nothing more than bicycle forks reinforced with various forms of link girders. The link girders provided limited vertical movement of the front wheel. Slowly, better systems were developed.
Front suspension systems come in three basic varieties: leading link, telescopic fork and swingarm. Leading link forks began appearing as optional add-ons to rigid forks. Leaking links are characterized by a fork pivot positioned behind the wheel spindle. Vertical wheel movement is allowed by the action of the link. Damping is then possible through some form of spring or hydraulic device. (You may have heard about an Earles suspension, which is a variation of leading link.) Although not common, this design is still in production and found on low end motorcycles and scooters, and the upper end retro-classic Harley FXSTS Springer.
Originally found on production motorcycles as early as 1908, the telescopic front fork did not become the standard until right after World War II. Most modern bikes use a double-acting internal spring telescopic fork. This type of fork uses a progressively wound coil spring fitted inside the fork tube to provide most of the suspension action. Components inside the fork are activated anytime load is placed on the front fork or whenever the front wheel receives a shock. Shock absorption is accomplished through spring action, air compression in an inner tube and resistance to the flow of oil forced into a cylinder by outer tube movement. There is a compression stroke action and an extension stroke action to provide constant shock absorption and rebound control. If both directions of fork travel were not regulated, the bike would buck uncontrollably. Front wheel swingarm design has only recently been introduced into mass produced motorcycles. Bimota and Yamaha lead the pack, but other manufacturers' designs are sure to follow. In this design, the steering and shock absorption functions are separated into two totally independent mechanical systems. This separation provides engineers the luxury of tuning each system to perform at maximum effectiveness.