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Bb Isis Or Square Taper


echo8

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Hi,

My mate has snapped about 4 square taper bb's in the space of around 3 months but dont worry he is about 6.5". i run square taper at the moment but i am just switching to isis, i would say go for isis if you have the money :) and like dan says they can also round of. I would rather have weak bearings knowing my cranks will not strip.

Moza

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Please use the search, this will be the 3rd thread ive posted this in.

The ISIS interface is inherently stiffer, and allows for the use of a larger diameter axle to increase strength. Unfortunately however, the larger axle means there is less room for bearings, so in most situations the load capacity of the BBs are reduced, or they don't last as long, or both. Various methods have been devised to prevent this, such as the external bearing BBs, although the mentioned SKFs seem the best on the market at the moment.

You are right about the actual taper causing problems over time. Square taper cranks work on a fully tapered interface, you can just keep going if the crank becomes slightly loose, wheres the ISIS taper has a much shallower angle, and actually has a stop, so unlike square tapers which you can keep forcing when the taper wears a little, the isis cranks push on and stop at a set point. If any play develops, which it can after a lot of use (accelerated by multiple removal of cranks) then there is no way of getting rid of it, the taper is permanently damaged. I've seen this happen to a few cranks, including middleburns. you undo the crank bolt and you can just slide the crank off, no need for an extractor.

Square has been around almost forever, and i think it will have its place for a long time to come yet, its simple, cheap, universally known and easy to maintain.

ISIS is a great solution for the more extreme ends of biking nowadays, which inherently have shorter lifespans on high stress parts such as cranks any way, so you may be able to justify the reduced longevity for the extra strength.

ISIS are more expensive as the Tapers profile is harder to manufacture, it is a more complicated shape and has to be made to a higher tolerance than square taper cranks.

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