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
