Drivetrain confusions of a beginner

[Paul]

I will shortly be having a bike put together, being a bit of a beginner I recognise my serious lack
of mechanical skill and will be having a professional mechanic put the thing together. I 'just' need
to get the components together.

The chainset will be a standard drive (26,36,48) Deore Octalink, easy enough. I am however a little
confused when it comes to the bottom bracket. The companion BB to the Deore chainset is the ES50/51
octalink. The frame that the bike will be built around has a 68mm BB shell so I know that I need a
68mm BB. However the ES50/51 comes in 2 axel lengths, 113 and 118 and I don't know which I will
need. The frame manufacturer's site says 113mm for MOST cranksets. I can't find the info. I need on
the Shimano site and was wondering whether anyone here could help? Once I have the correct
BB/chainset the rest should be fairly straight forward since the chainline should be correct, the
rest is just standard Deore fare.

To confuse me even further the Shimano website has standard and 'E' type octalink BBs, what is an
'E' type and how do I know if I need one?

Many thanks for any help and guidance that can be given.

With Kind Regards, Paul

 

[James Thomson]

"Paul" <[email protected]> wrote:

> The frame that the bike will be built around has a 68mm BB shell so I know that I need a 68mm BB.
> However the ES50/51 comes in 2 axel lengths, 113 and 118 and I don't know which I will need.

Longer bottom brackets are usually specced on bikes with oversized seat tubes. A fat seat tube
prevents the front derailleur from swinging close enough to the centre line of the bike to reach the
smallest chainring, so Shimano's solution is to move the crank outwards. You mentioned before that
your frame has a 28.6mm seat tube, so you need the shorter bottom bracket.

> To confuse me even further the Shimano website has standard and 'E' type octalink BBs, what is an
> 'E' type and how do I know if I need one?

An E-type bottom bracket is designed to work with an E-type front derailleur - a derailleur that
mounts to a special plate fitted to the bottom bracket, designed to avoid compatibility problems
with rear suspension designs and unconventional seat tubes. You don't need an E-type derailleur, so
you don't need an E-type bottom bracket.

James Thomson

 

[Paul]

Many thanks again James, I feel much more confident about going ahead and ordering up some
components.

Your help is much appreciated.

With Kind Regards, Paul.

 

[Bill]

Just curious when a seat tube would be classified as oversized. I have a 1 1/4" tube on my Trek 520
- is it oversized ?

Thanks

"James Thomson" <[email protected]> wrote in message
news:[email protected]...
> "Paul" <[email protected]> wrote:
>
> > The frame that the bike will be built around has a 68mm BB shell so I know that I need a 68mm
> > BB. However the ES50/51 comes in 2 axel lengths, 113 and 118 and I don't know which I will need.
>
> Longer bottom brackets are usually specced on bikes with oversized seat tubes. A fat seat tube
> prevents the front derailleur from swinging close enough to the centre line of the bike to reach
> the smallest chainring, so Shimano's solution is to move the crank outwards. You mentioned before
that
> your frame has a 28.6mm seat tube, so you need the shorter bottom bracket.
>
> > To confuse me even further the Shimano website has standard and 'E' type octalink BBs, what is
> > an 'E' type and how do I know if I need one?
>
> An E-type bottom bracket is designed to work with an E-type front derailleur - a derailleur that
> mounts to a special plate fitted to the bottom bracket, designed to avoid compatibility problems
> with rear suspension designs and unconventional seat tubes. You don't need an E-type derailleur,
> so you don't need an E-type bottom bracket.
>
> James Thomson