The Golden Wrench

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

Wednesday, January 20, 2010

Know Your Splined Bottom Brackets Part Two: Splines Go International

Shimano's legendary XTR 950 cranks found their way onto every conceivable type of bicycle. I've seen them on BMX bikes, observed trials bikes, downhill racing bikes with 8" of travel--even a touring bike for an elderly gentleman who needed lower gearing--and lots and lots of race-level mountain bikes. The technology trickled down to the XT 760, which had hollow arms that kind of looked like poofy bread sticks, and it looked like Shimano had another hegemonic stranglehold on the industry.

"See here!" retorted some industry malcontents with a loud retort, "why is it that we have to pay Shimano lots of royalties if we don't want our crank arms to do this..."

"...and this?!?!?"
And they dratted their luck, wondering aloud why they had left their beds and changed out of their jammies that morning.

Then one day at a local Las Vegas Denny's restaurant (they're all local: visit one and ask, "Is this a local Denny's restaurant?" An employee will nod slowly and say "Indeed.") the fellers from TruVativ and Race Face, as well as the guy who started Chris King (his name eludes me temporarily... oh well) all bumped into one another . It was a bit of a kerfuffle getting all the tables arranged so they didn't have to holler across the dining room, but over some sumptuous Grand Slams they all agreed that a new standard must be born.

During the feast, a spirit of dejection hovered over the group like an ominous cloud. The Big Red "S" had shown up at Interbike with little Nasty-Grams printed on card stock and handed them to all the other crank and BB manufacturers present. The text read thus:

Har-dy Har har, American drive train fashioners, on account of the throat-grip of the industry in my possession! We are indeed willing to extract joyfully the excise of currency for to lend from us the patents and allow the both of you to make sloppy American crankshaft arms to fit glorious Shimano wonderful bottom-set! As though it were probable. Tee! Hee!

Have a day which is niece,


To add insult to injury, the messengers were wearing XTR t-shirts over top of their polo shirts, which made them look like elementary school chaperons. It was a truly demoralizing scene.

Breakthrough occurred during some typical bike industry breakfast tomfoolery. Hoisting a sausage aloft, one of the Race Face guys said "If I put ten splines on this, tapered them one degree, and made the splines match the width of the entire crank arm, it would be delicious wrapped in half of a pancake." He was clearly joshing, but the table fell silent for several moments. It was as though Providence had spoken, and soon napkins became drafting-boards, conversation turned to fatigue life and bearing diameters, and a new standard was born. They agreed to make the design public domain since everyone was too stuffed and amiable-feeling to roshambo for the rights. In honor of the matron-goddess of Egyptian mythology (patroness to the downtrodden), they named the new interface ISIS. Other contenders for the name included "Eat Our Collective Shorts, Big Blue 'S,'" "Super Duper Spline-O-Mat 1999," Phil Niekro" (after the legendary Braves knuckleballer), and "Ten Fins On This Shark, Homeslice."

You could read about it here if you want to really be a bike nerd.

You may be saying to yourself, "what about those el-cheapo splined hunxajunk that came on my low-end rig in 2004?" You'd probably be referring to Powerspline, a 12-splined interface developed by Truvativ and limited to low-end units. Otherwise, you may be suffering from a brain injury and only think that you have a bicycle. Either way, apparently Powerspline was easy to manufacture.

Another interface was born of an inherent weakness in the ISIS design: bearing life. Since the ISIS spindle was much larger in diameter than typical square taper units, bearings had to become smaller to accommodate it. Smaller bearings meant shorter lifespan, especially in big-hit riding like downhill and freeride, where finesse may be a favorite hair product but means nothing on the trail. The spindle ends were just a tad smaller so that more material could be used in the cranks themselves, and the bearings moved outboard. This is known as the Howitzer system.

So now you know maybe a bit more about splined cranks. Study up: there may be a quiz!

Click on the pictures to make them REALLY BIG... you'll thank me!