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International Spline Interface Standard
ISIS Bicycle Crankset Standardization?

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:

  1. 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.
  2. 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.
  3. 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.
  4. 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

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copyright Jan. 2007