Join Date: Oct 2003
Bikes: 03' BigHit Comp/DH
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Choosing the right bottom bracket
When choosing a new bottom bracket or crankset, you must take note of the varying standards used to attach the crankset to the bottom bracket, as well as shell width. There are currently 3 competing standards used to attach the crank to the bottom bracket:
The I.S.I.S. international standard is used on bottom brackets from Race Face, Truvativ, and others. I.S.I.S. uses a splined system similar to (but not compatible with) Shimano. I.S.I.S cranks and bottom brackets are available from a variety of manufacturers, including Race Face and Truvativ.
The Shimano system also uses a splined interface. It is not compatible with the I.S.I.S. standard. Within the Shimano system, two incompatible standards are used:
Shimano V1 spline - Used on the XTR line of components. Only XTR cranks will fit on XTR bottom brackets.
Shimano V2 spline - Used on the Deore XT and LX line of components. XTR cranks will not fit on the XT and LX bottom brackets.
Because of the incompatibilities between various Shimano components, it is best to choose the same model of bottom bracket and crankset. For example, if you plan to use XT cranks, you should also purchase an XT bottom bracket.
Conventional square taper bottom brackets are becoming less common on both mountain and road bikes. This equipment can be identified by the square mounting hole in the cranks and square shape of the bottom bracket spindle.
Bottom Bracket Shell Width
Bottom bracket shells come in varying sizes. The most common are 68mm and 73mm. Many bottom brackets (Race Face, some Shimano, Truvativ) can accomodate either size shell. Others (some Shimano) need to be ordered in a seperate size depending on the size of the bottom bracket shell. Measure your frame to be certain prior to ordering.
When installing or removing a bottom bracket, you must be aware that most frames are REVERSE threaded on the drive side of the bike. This is the opposite of most fittings on your bike.