Which bottom bracket?

[helston90]

It appears after around 3000 all weather miles the bottom bracket on my Giant Rapid 4 needs changing,
according to the specs it's currently got a FSA BB-7420ST - 116mm,

How can I tell what I can replace it with? Does it have to be like for like or would any of the Shimano UN series fit so long as it's the 116mm square taper?

Trying to find a deal as money is tight so just trying to suss out what I can get.

Cheers,

 

[PpPete]

UN55 is the one to go for. Very little more expensive than UN 26 and lasts seemingly forever.
116mm sounds a bit odd though.
113 and 118 are the popular ones, CRC do offer a 115mm which is probably close enough to make no difference

 

[RecordAceFromNew]

UN55 is the one to go for. Very little more expensive than UN 26 and lasts seemingly forever.
116mm sounds a bit odd though.
113 and 118 are the popular ones, CRC do offer a 115mm which is probably close enough to make no difference

+1. Shimano used to do 116mm (code YL in Shimano speak) square taper but no longer it seems. The 115mm is 1mm shorter on the drive side, while the 118mm is 1mm longer on each side.

 

[helston90]

The 115mm is 1mm shorter on the drive side

Will this not make a difference to the fit? I know it's only 1mm but I don't want to run into problems on my first BB change.

 

[themosquitoking]

I'm guessing from some of the replies, bb donut myself, that the actual length of the bb shell on the bike is the same it just depends on how much protrudes out of the shell.

 

[RecordAceFromNew]

Will this not make a difference to the fit? I know it's only 1mm but I don't want to run into problems on my first BB change.

Plus or minus a mm or two to the chainline is usually not a problem, but if you wish to be sure you can check to see if your front mech can under or over-reach by adjusting the limit screws and cable tension.

Before ordering it is worth measuring the existing chainline, and actually check the bb dimension and not just rely on a bike's advertised spec.