SS Chainline/BB?

[Aaroneous]

So I've got almost all the parts to build up my SS, but I haven't figured this out yet...
I just got the rear wheel yesterday - Surly hub, Sun CR18, DT spokes :D - from One on One (Thanks, guys!), and I need to figure out what size BB I need to get the perfect chainline.
According to Sheldon - http://sheldonbrown.com/chainline/index.html - the rear chainline measurement of the Surly hub is 46.5mm. I understand how that's measured, and I can throw a freewheel on there and get the exact measurement to double-check.
I also get that you measure the front chainline from the middle of the seat tube to the middle of the chainring...

BUT, how do you translate that measurement to BB size?
Thanks for any advice...

[bigwheel]

So I've got almost all the parts to build up my SS, but I haven't figured this out yet...
I just got the rear wheel yesterday - Surly hub, Sun CR18, DT spokes :D - from One on One (Thanks, guys!), and I need to figure out what size BB I need to get the perfect chainline.
According to Sheldon - http://sheldonbrown.com/chainline/index.html - the rear chainline measurement of the Surly hub is 46.5mm. I understand how that's measured, and I can throw a freewheel on there and get the exact measurement to double-check.
I also get that you measure the front chainline from the middle of the seat tube to the middle of the chainring...

BUT, how do you translate that measurement to BB size?
Thanks for any advice...

I don't have the complete answer, but the Race Face crankset comes with directions and numbers, where you tell it the chainline measurement and the width of your bottom bracket (on your frame), and it tells you how many shims you need put in. Also, Park has a tool for measuring chain line.

[funky-funky-chicken]

That depends on the manufacturer of your crankset. In my personal experience, dealing with chainline and most ISIS type cranks is a PITA, square taper is much easier. With ISIS, your choices for length are relatively limited, much moreso than with "old fashioned" square taper. If you can find the information for the brand and model of crank that you own, you can "calculate" what you will need for a BB length. You could read the spew over on Surly: http://www.surlybikes.com/spew5.html for a good example for options on how to deal with chainline.

In my experience... I have a whole box of sqare taper BB that I use for experimentation purposes until I can get the chainline exactly right.

[Aaroneous]

I'm going square-taper for sure - I've already got a couple different cranks, and there's no better BB value out there than a good ol' UN-53.
I'm probably not going to find any size info on the 20 year old Suginos I'm gonna use...
I guess what I really need is a whole box of old BBs... ;)

I do have a 118, so maybe I'll throw that on there and see what it looks like. I was just hoping there was a magic formula that would help me avoid trial & error...

[funky-funky-chicken]

I guess what I really need is a whole box of old BBs... ;)

I do have a 118, so maybe I'll throw that on there and see what it looks like. I was just hoping there was a magic formula that would help me avoid trial & error...

Use your 118, then measure to see how far off you are. If you'd like to move your chainring in or out (say 5mm) then you know you'd need a 113 or 122 for example.

[Aaroneous]

Ended up needing a 127.5mm BB - seems crazy-wide, but lines up darn near perfect...

[mtnbykr]

... I have a whole box of sqare taper BB that I use for experimentation purposes until I can get the chainline exactly right.

i use the race face adjustable bb in square or isis and dial it in until the cl is perfecto.

kl

[Aaroneous]

i use the race face adjustable bb in square or isis and dial it in until the cl is perfecto.

kl

But I bet those are more than $20. ;) UN-53 for life, baby!

I just read your other post about your back. Holy f-ing s, dude! Best wishes and heal fast...

[mtnbykr]

But I bet those are more than $20. UN-53 for life, baby!

I just read your other post about your back. Holy f-ing s, dude! Best wishes and heal fast...

yea just a little more than $20 :?) but they last me forever. i've only had 1 die in 8 years and i have 3 of them in action now.

thanks for the thoughts. it's gonna be a long fall/winter.

kl