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To ISIS or Not To ISIS?  To
ISIS or not to ISIS is not an easy question. You increase the bb
spindle and you get more stiffness that is pretty much a no-brainer.
You increase the spindle and then drill it out. Two things come into
play: #1, I need to make the pipe as stiff as the solid spindle and, #2, I
need to make sure I don't crimp the hollow spindle when I drop a pedal.
In most major accidents the crank and or the ISIS spindle bite the big one, but there is enough insertion on the ISIS to prevent dropped pedals from ruining things. It is the bending force in a crash from big side load that kills things. The only reason for ISIS is to shed weight at this point. The spindle gets lighter and so can the crank to spindle interface. Campy carries quite a bit of pork in the crank arm spindle eye for the bb spindle interface. The big payoff on Campy is bearing resistance. Most ISIS internal guys are using a roller bearing to prevent the pipe from flexing at the bearing and causing a high stress and ware point. The use a ball setup to center the pipe in the cups. The drag from that bearing setup is huge. A Campy bottom bracket compared to a Dura-Ace is over 4 times as much drag (for the ShimaNO unit) with a 170-pound rider. There is no real problem with small bearings in a bottom bracket except for drag. As the bearing size decreases the drag goes up. Campy may be old school, but they can at least think beyond a gram of weight. If you move the bearings out board you can increase the size again and start reducing the drag. You still have a similar problem even outboard with supporting a hollow axle, but you are at least addressing the drag issue a little. If you can get the support point close the the crank you can decrease the roller bearing size and reduce drag again. It is still not as good as Campy. There is only so much you can do. You either go after drag or weight and work on the compromise. |