In the late 1990's three bicycle parts manufacturers took a huge
leap of faith and came together to discuss the concept of a standard
set of measurements and designs for the bottom bracket and crank
arm interface. In 1998 Truvativ, Chris King and Race Face did
succeed and put on paper the ISIS crankset drive standard. What
does it matter?
What the ISIS crank set standard stipulates:
- What most cyclists noticed was that the ISIS standard created
a standard spline pattern on the end of the spindle. The geometry
required a constant outer diameter shaft with 10 evenly spaced
flutes machined into each end of the spindle.
- A shoulder must be machined into the spindle exactly 16mm
from each end of the spindle to provide a constant stopping
point for the installation of each crankarm.
- The standard dictated a series of standard spindle lengths
and the associated measurements between the crank shoulder and
the spindle center line. This effectively dictated a predictable
position of the crank arm relative to the frame centerline,
for any standard spindle length.
- Two sizes of attachment bolts were drafted into the ISIS standard
to offer greater flexibility for road vs mountain bike design
decisions. ISIS drive cranks are compatible with either an M12
or M15 bottom bracket. The smaller sized M12 bolt will create
a stronger spindle due to the thicker wall possible within the
spline geometry.
Note: that the attachment bolt should be supplied with the bottom
bracket to assure that the threads match.
What it was NOT!
This design standard does not encompass any issues related to
the size or configuration of the bearings in the bottom bracket.
They can be a sealed cartridge or needle bearing or bushings entirely
up to the fabricators of these bicycle components.
Advantages:
It created a common connection between the spindle and the crank
arm that made it easier to swap parts between different bikes
and different manufacturers. For you and I this created less obsolescence,
and easier bicycle part upgrades.
This standard created more predictable results in the positioning
of the chainset relative to the center line of the bike frame
and thus more precise alignment with other parts of the drive
train.
The standard was left in the FREE public domain so many manufacturers
could gain marketing advantage of creating bicycle parts recognized
as complying with a more universal standard. For you and I that
makes the prices come down.
Thus when buying bicycle parts
ISIS offers one piece of clarity when choosing different crankset
components made by different suppliers.
Related Articles:
Bicycle Cranksets:
Bottom brackets, cranks & chainrings
