Blowing Bottom Brackets

Blowing Bottom Brackets

Reader Bill asks “Our rear bottom bracket on the tandem bicycle has seized… my question would be, did water get into the bottom bracket and freeze it up? If so, what would be your recommendation of replacement?” After a few hundred tough miles on the mountain bike tandem the downhill type bottom bracket has failed leaving their tandem bike team with the same question that faces most hard-core tandem teams early on, what is the right bottom brackets for our needs?

The answer starts with basic physics. Tandem teams, notably tandem mountain bike teams, place a huge amount of rotational and torsional stress on the bottom brackets. With the standard left side stoker to captain chain and the drive side chain on the rear bottom bracket this component experiences stress it was not designed to handle.

Standard bottom bracket designs incorporate two bearings, one on each side, that allows the spindle to rotate smoothly. In some cases the drive side bearings are designed to withstand more stress. Heavier duty bottom brackets take this drive side support up a level with dual drive side bearings and a single bearing on the non-drive side. For tandem teams this solution still does not resolve the problems with added stress to the non-drive side of the equation.

Currently there is only one viable alternative that affords tandem teams a usable option for the bottom bracket. FSA manufactures a quad bearing bottom bracket. With four bearings set into two on the drive side and two on the non-drive side tandem teams are afforded added durability to the bottom bracket.

In the case of this reader’s question the timing of the bottom bracket failure coincided with heavy rains in the area. The assumption one can easily make is that the bottom bracket failed as a result of the rain when the real cause was probably premature wear from the vigors of tandem usage. Replacing the part with a quad bearing FSA bottom bracket should improve longevity for this team.



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