Cranks & Bottom Bracket Length

[Rich B]

I currently have a 127.5mm (Shimano UN51) tapered square bottom bracket on my bike. I am considering
replacing the crank with a current vintage Shimano XT or LX which take a splined bottom bracket. The
longest Shimano splined bottom bracket I can find is 118.5mm. Question – Do differences in the
cranks between what I have now and the new XT or LX account for the difference in bottom bracket
length or can I not use one of these cranks ? On the Shimano web page, they list chain line
dimensions. Is this what I need to key off of ?

Thanks
Rich

 

[Paul Kopit]

The bb lenght is crank specific. You need the 118.5 for a triple.

On 31 Mar 2003 17:55:40 -0800, [email protected] (Rich B) wrote:

>current vintage Shimano XT or LX which take a splined bottom bracket. The longest Shimano splined
>bottom bracket I can find is 118.5mm.

 

[Robert Quindazz]

Actually they make a 113mm for that spline style also (which is only found on XT and LX cranks). I
would try to use the shorter one if possible as those cranks have a pretty wide "Q" factor. I use
the 113mm one on my touring bike with an XT crankset.

http://www.performancebike.com/shop/Profile.html?SKU=6288
http://www.pricepoint.com/bbracketsmtb.html

On Tue, 01 Apr 2003 03:48:52 GMT, Paul Kopit <[email protected]> wrote:

>The bb lenght is crank specific. You need the 118.5 for a triple.
>
>On 31 Mar 2003 17:55:40 -0800, [email protected] (Rich B) wrote:
>
>>current vintage Shimano XT or LX which take a splined bottom bracket. The longest Shimano splined
>>bottom bracket I can find is 118.5mm.

 

[Jim Price]

Robert Quindazzi wrote:
> Actually they make a 113mm for that spline style also (which is only found on XT and LX cranks). I
> would try to use the shorter one if possible as those cranks have a pretty wide "Q" factor. I use
> the 113mm one on my touring bike with an XT crankset.

Two things:
1.The Octalink 2 spline pattern is also available on the Deore chainset. Many people don't seem to
have updated this information on their web sites etc. (possibly because the Deore chainset came
out after the LX and XT ones?).

2.5mm is also the difference between a 68 and 73 mm bottom bracket shell. If all else stays the
same, you would need the longer axle in the wider BB. I bet they don't do the 113 for a 73 mm BB,
on the assumption that it may foul the cranks.

The only reason I can think of to use the 68/118 is if you use really large chainrings, which would
otherwise foul your chainstays.

> On Tue, 01 Apr 2003 03:48:52 GMT, Paul Kopit <[email protected]> wrote:
>>The bb lenght is crank specific. You need the 118.5 for a triple.

Surely the shorter length for the triple, and the longer length for using the same crankset as a
double, to keep the chainline optimised? The road splined chainsets are of a different pattern, and
not interchangeable, IIRC.

I've got this setup in Deore with a 68/113, and its very impressive, especially when its available
mail order for less than £60 for the chainset and BB.

JimP

 

[Qui Si Parla Ca]

rbruvee-<< Question – Do differences in the cranks between what I have now and the new XT or LX
account for the difference in bottom bracket length or can I not use one of these cranks ?

yes, the crank design determines the BB spindle length- Get the Bb that gives you proper chainline
and proper fder action-probably a 118mm but perhaps a
113mm...

Peter Chisholm Vecchio's Bicicletteria 1833 Pearl St. Boulder, CO, 80302
(114)440-3535 http://www.vecchios.com "Ruote convenzionali costruite eccezionalmente bene"