[Closed] Chainlines?

Sheldon knows;

[url= http://sheldonbrown.com/chainline.html ]http://sheldonbrown.com/chainline.html[/url]

Sheldon knows more...

http://sheldonbrown.com/bbsize.html

PaulD

Helpful thank you. I measured the chain line this evening and it looks like 45mm, although it is very dark out there! I have a Shimano UN55 bottom bracket fitted which is a 68mm body and a 113mm spindle. Reading the product specifications it seams that for the Shimano Alivio M411 chainset I have I need between a 47.5 and 50mm chain line. Does this seem right? If so would I use a bottom bracket with a 115mm spindle?

p,

You are probably correct as it is.
I favour the middle ring being in line with sprocket 5 (9-speed) or 1 sprocket further inboard to give a good line when under most torque.
Not worth swapping 113 for 115 unless a ring is touching the chainstay under load.

The reason given for Alivio needing/offering a chainline of 47.5 and 50 is to allow for different width rear hubs. These have increased over the decades from 120 (5-speed) to 135mm (current 10/11spd), excluding DH frames at 150mm.

PaulD

Hey,

Thanks for that. On closer consideration the specification says for a 50mm chain line and a 123mm spindle, however the bikes websites suggest a 118mm spindle.

Thanks

Your earlier measurement was spot on at 45mm.

You may find the front mech will not go inboard enough to drop to the granny.

If this is too far inboard, and you will know if you fit it and it feels or plain looks wrong, I offer you a solution;

I have a brand new in the box UN54 68x122 that I will swap if your UN55 is close to new.

We each pay our postage.

Let me know.

paul.r.davisAThotmail.co.uk

Hey,

Thanks for the offer but I had already ordered a 118mm bottom bracket on the basis of SJS website and due to the fact that I am only running a 7 speed cassette.

Thanks