Previewed: Fifteen.G Cranks and Bottom Bracket

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After more than two years in development the new Fifteen.G cranks are going into production and will be available for sale early in the spring. Fifteen.G is the mountain bike brand of a product design collective known as The Hive.


The cranks come in the triple-ring setup, shown here, or a single-ring configuration with a bashguard. The triple weighs in at 711 grams and the single tips the scales at an odious 666 grams.


But the real story with the crank lies in its spindle interface, which, while innovative in its execution, is not the first time a tapered polygonal interface has been tried on a bicycle crank. Some might remember Grove Innovations’ try a crank with a similar tapered, three-sided spindle. But if you don’t, you’re not along, because the system, which relied on an—ahem—*spindlier* steel axle and bottom bracket bearings small enough to fit into a bottom bracket shell (kids, ask your parents), tended to blow out bearings and never caught on.


Fast forward a technological generation in manufacturing advances and behold a beefier, more precise 30-millimeter diameter axle, which runs on bigger, externally-mounted bearings. The Fifteen.G cranks use the same 30-by-42-millimeter bearings as the up-and-coming BB30 standard—long used by Cannondale and now being hyped and pushed by components companies like Full Speed Ahead and being adopted by more and more frame manufacturers taken by the promise of lighters, stiffer bottom bracket interfaces.


But the beauty of the Fifteen.G crank is that it works with any conventional 68- or 73-millimeter-wide bottom bracket shell. The package sells for $295 with a 32- or 34-tooth chain ring and a corresponding-sized bashguard. The triple shown here will set you back $275, and the bottom bracket is sold separately for $70. The crank uses 4-by-104 millimeter chain ring spacing, and is available in 175- and 180-millimeter crank arm lengths.


Buy the whole kit together and you get this trick installation tool for the bottom bracket, which also includes a 15-millimeter pedal wrench, and a socket slot for torquing the BB to spec. (If you loathe the idea of more specialty tools, fret not—a 1-3/4-inch 12-point socket will also do the trick on install. And a free pedal wrench is nothing to scoff at.)


The advantage of using the tapered polygonal interface, as it’s technically called, is that it makes for a 100-percent contact connection between the crank and spindle. With an interface like the fast disappearing ISIS standard, a compression fit between a steel spindle and an alloy crank arm, over repetitive press-fits, leads to corrosion between the grain boundaries of the respective components, and, eventually, slop in the connection or failure. Given the tight tolerances of the Fifteen.G interface, there is only 1.6 millimeters of space to be taken up while torquing the crank arm to the spindle. With ISIS-style connections, there is between 3 and 6 millimeters to compress to get a solid fit.


The Hive also produces trick super-wide flange singles-peed hubs under the Chub brand name and is working on road bike components under the REVL name, but these cranks are the first Fifteen.G products to market. Availability of the cranks is expected to be March 1. Keep an eye on www.bythehive.com for more.


LINKS:
Full Speed Ahead: fullspeedahead.com







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