Buying a new bottom bracket

[MontyVeda]

The last time bought a new BB was because I'd bought a new set of cranks with a splined fit instead of a square one... so i went to a bike shop and bought a splined BB.

today i went to my LBS to buy a new splined BB for a 68mm shell.

"What kind of spline is it?" Mr LBS asked.

"er...." I repleid, adding, "They're truvative cranks."

his assistant said something along the lines of 'octodrive'

I said "it has isis drive written on the cranks" somewhat confused.

Then they asked what width my axle was.

"er..." I repleid, adding "does it matter?"

Ten years back when I bought the BB I'm looking to replace I'm sure the conversation in the LBS went along the lines of:

"Have you got a splined bottom bracket?"

"Yes"

"how much?"

"a tenner."

"Cheers."

And i left with a new BB, went home and fitted it.

I have no recollection of being asked about axle width or which kind of spline.

So my question is (or questions are...)

As long as the shell size is correct, does the axle width matter?

And what type of spline does a Truvativ FireX crank from 2002ish have?

Today the bloke said Octodrive which suggests 8 splines, but i can count 10 in my cranks.


It never used to be this hard to buy a BB

 

[potsy]

Sounds like an Octalink BB, same as my Secteur, the width should be stamped on the old one but you'll need a tool to get it out.

 

[boydj]

Octalink (Shimano) and ISIS are two different standards. Bike shop should have been able to work out what you needed from the info you provided - 68mm ISIS

 

[RecordAceFromNew]

You need ISIS. ISIS BBs do come with different spindle lengths (103mm/108mm/113mm/118mm etc.). You need to get the right one to maintain the right chainline, otherwise you could end up with all sorts of front shift/clash problems. If existing BB is ISIS and works with the chainset just measure existing spindle length, else you will have to find out from make and model of chainset and desired chainline which length you need.

 

[MontyVeda]

cheers chaps!

most helpful as usual.