Chainline/bottom bracket/Sugino 75/ISO/question
 

So, let me get this straight. Eric Sovern from Surly has said that the Surly rear track hub is spec'd to give a chainline of 42.5-43.5 mm. I bought a Steamroller complete, and am interested in getting Sugino 75's instead. I know for Sugino 75's, I need a 109mm spindle ISO taper bottom bracket to get a 42 mm chainline. I also know the Steamroller complete's current BB is 68x103mm so it's 68mm wide.

So, to get a 43mm chainline for the 75's, in order to match the Surly track hub's 42.5-43.5mm, I would need to get a 111mm ISO taper bottom bracket to use with the Sugino 75's, because every 1mm increase in spindle length increases chainline by 0.5mm, right? Would any ISO taper bottom bracket do?

For example:

Campy Veloce BB 68x111mm, ISO Taper (gives 43mm chainline)
http://aebike.com/page.cfm?PageID=30...ils&sku=CR9647

Or, this Miche Primato Track BB 68x110mm, ISO Taper, (gives 42.5mm chainline)
http://aebike.com/page.cfm?PageID=30...ils&sku=CR1621

How come nobody has suggested using the Miche Primato Track BB as a cheap ($20) alternative to buying a Sugino 75 or Sugino 68 BB?? Is there something I'm missing here?

miche works for me on my Bareknuckle, I know I suggested its use in another thread about it. I don't feel like finding the thread right now, but it works. I have Phil hubs, Sugino 75 Crank, with Miche bottom bracket. I think my chainline is something like 41.5.

if you want a standard track chainline, you'll want to get the 109mm sugino bottom bracket. It will realistically put the chainline at about 42.5-43mm

Okay, so, when someone says the standard track hub creates a chainline of 42mm, is this the measurement without a cog? So the true chainline *with* a cog will be like 44mm or so?

Or, when someone says the standard track hub creates a chainline of 42mm, this is including the cog, and should match up perfectly with a chainring spaced exactly 42mm away (e.g. Sugino 75 + 109mm BB).

business cycles has a pic of how the chainline is measured.

yeah, i've looked at it twice, but it still does not address whether when people say "42mm standard track chainline" if it includes the cog in this width, or if it just assumes the cog adds on a couple extra millimeters for a true 43-45 chainline..

chainline is measured from the centerline of the frame to the cog.

if you don't have a cog mounted you can't have a chainline
much like if you don't have a crank mounted, you can't measure chainline.

"standard" 42mm chainline is an approximation to begin with. different cog+hub combinations will produce different chainlines even if they are all designed around a "standard". most of these combinations will be somewhere near 42ish mm

thanks, makes sense. i guess i was being stupid. the chainline is exactly where the chain will go, so obviously to the cog. yay.

I would get the 109, put the cranks on it with a torque wrench, and then measure your chainline. If it needs to go out, put in a BB spacer and call it a day. Also, make sure your BB shell is faced.

Also, most frames aren't aligned precisely enough to be worth worrying about chainline being .5mm off or something like that.