Bicyclists that ride bicycles in races or over rough terrain may desire to equip their bicycles with shock absorbing front forks. A special shock absorbing fork may be purchased by the bicyclist and he or she will simply remove the standard fork and replace it with the shock absorbing fork.
The bicycle fork connects the front wheel to the frame of the bicycle and to the handlebars which act through the fork to steer the front wheel. The fork includes a strut on each side of the wheel that extends from the wheel axle to a crown that overlies the front wheel and which secures the upper extends of the struts together. A steerer tube extends from the crown upwardly through a head tube on the front of the frame and then interconnects with the bicycle's handlebars.
The shock absorbing fork provides the struts with spring movement for absorbing the jarring action incurred when the front wheel encounters a rut or rock which would otherwise be directly transmitted to the rider through the rigid struts and steerer tube.
There are many different brands and sizes of bicycles with different fitting requirements as between the fork's steerer tube and the bicycle's frame hub and handlebar. However, the struts and crown portion of the fork are fitted to the wheel of the bicycle. Many different brands and even sizes of bicycles are equipped with the same wheel size.
The problem that the above creates is that the manufacturer, dealers and retailers of shock absorbing forks to be retro-fitted onto bicycles, either have to produce and stock a wide variety of full fork assemblies for the different bicycle brands or provide for a common crown and strut subassembly and the capability of interchangeably assembling a variety of steerer tubes to the subassembly. In this latter event, a sufficient quantity of the struts and crown subassemblies (the more expensive components of the shock absorbing fork) can be stocked for universal application and a wide variety of the less expensive steerer tubes can be separately stocked for selective assembly to the crown and strut subassembly as needed.
Heretofore a typical method for interchanging steerer tubes involved the provision of slots in the crown with pinch bolts and sleeves to accommodate different diameters of steerer tubes. The slot weakens the crown causing unwanted flex and stress concentrations. A high degree of stress is generated in the fork assembly at the connection between the crown and steerer tube and accordingly the steerer tubes are typically made of high strength steel which is relatively heavy and undesirable for bicycle construction for that reason.