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Bicycle Crank Set
The History of Technological Inovation in Bicycle Crank Set Design?

The bicycle crank set is the power center of the bicycle. Parts are designed to transmit power from human pedaling to the drivetrain. Thus cranksets must be efficient in energy translation and at the same time support the weight of the driver when standing, or maybe if you persist in bunny hopping… when landing. So what technology have bicycle component manufacturers developed to add power and speed to the cycling experience?

The original cranksets in older and cheaper bicycles were a one piece fused assembly of two crankarms and a solid steel spindle. Although it was great for durability, nothing ever came loose; it added a huge amount of weight to the bicycle and was not flexible enough to allow for maintenance.

This changed when most mid-range bikes, converted to a crankset consisting of a separate bottom bracket assembly, matching cups for installation and a separate set of crank arms. Usually you were given a list of chainring options to complete the chainset. This created what was referred to as a 3 piece chainset; two arms and one spindle-bearing assembly.

This offered more upgrade potential. The sealed bottom bracket could be swapped in and out if the bearing wore out and crank arms could be replaced or upgraded. A solid spindle was essential for rigid performance but added a huge amount of weight and technicians were starting to look for a way to incorporate a hollow spindle into the design.

The diameter of the existing spindle was too small to offer the necessary strength and rigidity if the middle of it was bored to create a hollow design. The solution was to reduce the size of the bottom bracket bearings to create more room for a larger spindle, but the smaller bearings didn't last as long and required ongoing repairs.

 

Shimano and RaceFace addressed this challenge by placing the bearings outside the bottom bracket shell to give plenty of space inside the shell to enlarge the spindle. A side benefit was the increase in spacing between the bearings making the drivetrain more stable.

But the hollow spindle created huge design challenges to get a reliable connection between the spindle and the cranks. It was necessary to shift from the traditional solid taper-end to a splined hollow spindle end with more surface area to address this concern for greater rigidity and reliability.

Current innovations in bicycle componentry have fused the right crank arm to the axle eliminating entirely the problem and weight of bolting a crankarm to the drive side spindle. The spider-chainset combination is pre-mounted, and this creates what today we refer to as a 2 piece crankset. (they don't really include the bearing assembly as part of the story)

Check out the new Campagnolo Centaur Ultra-torque Crankset. It has taken the design further splitting the axle at the mid point of the bottom bracket shell and allowed Campagnolo to fuse both spindle-crank connections eliminating all crankarm bolts. This has offered significant weight advantages over traditional designs.

Related Articles:
Bicycle Crank Set: Bottom brackets, cranks & chainrings

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copyright Jan. 2007