The Golden Wrench

A blog about bicycle repair and maintenance by the mechanics at Freewheel Bike.

Tuesday, January 19, 2010

Know Your Splined Bottom Brackets Part One: Shimano

For a long (and, dare I say, happy) chunk of history, the world was content and complacent with square-taper technology. There were two formats to choose from: you could either use Campagnolo's standard (aka "ISO," which stands for "Icebergs Smooshed Ostriches"):

or you could use everybody else's standard, the venerable JIS (which stands for "Jiminy, It's Spring!" because that was the time of year when it was developed).

You may be saying to yourself, "Why, those are clearly both 2 degree tapers: why are they not compatible?" Spoken like a gentleman: a nobler interjection was never made. If you look closely, you will notice that the measurement across the flat is slightly greater on the JIS than on the Campy spindle. In other words, your Campy crank would only go about halfway onto a JIS spindle, and a JIS crank would bottom out on a Campy spindle. I've seen people try to do both, and I felt about the same as I do when I see people ice fishing in early May or golfing in thunderstorms.

Square tapers ruled the universe until about 1992, when upstart engineer Alex Pong began making Magic Motorcycle cranks for Cannondale. These CNC'd beauties featured hollow arms, a splined interface, and external bearings. [Shimano engineers took note and set an alarm clock for the day that Pong's patents ran out, but that's another story.] They were also prohibitively expensive: one could barter a lesser-known Canadian province for a set of Magic Motorcycle cranks without chainrings, but only if one was a handsome devil.

Shimano came out with their version a few years later: the dark gray XTR 950 cranks that everyone drooled over. Splines were emerging in a legitimate high-end category. Trickle-down occurred over the next several years, and behold! The world was introduced to Octalink V-1.

As you can see, the actual splined interface is kinda wimpy in this particular design. Shimano released a tech bulletin which said: "Hmmm... Current design soft in the somewhat like green willow branches. We make spline greater valley in steel much more of an occurrence to be reckon with, and rigidness shall go forth in peals of hoot and hollering joyful, with a strapping mans' quadricepts bellowing right joyful." And thus, Octalink V2 was born. Incidentally, Octalink V2 uses the same spline as the old XTR 950 used, but who's going to tell you that?

Much deeper splines, plus a pleasant minty fragrance (only available in Japan, sorry) set this interface apart from the V-1. This interface was king until Shimano released two-piece XT M760 cranks a few years later (Bullseye? Sweet Wings? Where are the lawyers?).


We'll take a look at non-Shimano splined interfaces.