thehugoball

Technically this is not a singlespeed or fixed-gear question because I'm building this bike up as a three speed, but I figured this category would be the most likely place to find single chainring and cog chainline experts. So the frame is a Raleigh Record from the late sixties that was originally a ten speed and the crank I'm using is a Sugino Super Mighty. Anybody know what the proper chainline would be for this set up? I am having the bottom-bracket shell re-tapped and faced so it will accept a standard English-thread 68mm bottom bracket. I need to figure out the appropriate spindle length. Any information and/or suggestions are greatly appreciated. Thanks!!!!

coelcanth

you're using a nonstandard setup..
you'll have to take measurements yourself

take the rear hub you're intending to use and calculate the chainline it requires.
measure the distance from the inside of the dropout (outside of the locknut) to the center of the cog.
(sturmey-archer hubs have some adjustability with their two spacers and flippable cog)
subtract this from one-half of the rear dropout spacing measurement.
make sure the hub is spaced for your application or modify it to be so..

if the rear hub needs a 42mm chainline and the super might crank requires a 109mm spindle for 42mm chainline, then you need a 109mm spindle..
if the hub can only be setup with a 43mm chainline then you need 1mm more on the driveside of the spindle to space it out (2mm more width on a symmetrical spindle)

remember, 1 or 2mm variation in chainline might not be a big deal in the long run,
and you can make adjustments by varying the orientation of the cog and/or washers
or even by using a spindle of a taper different than that originally spec'd for your crank

thehugoball

"if the rear hub needs a 42mm chainline and the super might crank requires a 109mm spindle for 42mm chainline, then you need a 109mm spindle.."

How do I find out what the required chainline is for this particular crank? Is there an online database? I haven't found one anywhere on sheldon brown's website. Thanks for the quick and concise response!

Sheldon Brown

There is no "required chainline" for a crank. You can vary the chainline of any 3-piece crankset by choosing an appropriate bottom bracket length.

See: https://sheldonbrown.com/chainline and https://sheldonbrown.com/bbsize

You need to start, as the prehistoric fish mentioned, buy determining the chainline of the hub. 3-speeds generally use chainlines in the 40-42 mm range. The chainline is usually adjustable at the hub by flipping the sprocket or re-arranging spacers.

The key is not to have any specific chainline value; the key is to have the front match the rear so the chain runs straight.

Sheldon "Straight Ahead" Brown

thehugoball

Thanks Sheldon!

Landgolier

What Sheldon said. Unless it's a current or well know crank (though yours sort of is), you're usually better off just popping the drive side arm onto a known BB, measuring, and doing the math. If you don't have any old BB's hanging around, take your problem to the LBS, they ought to be willing to put it on some old piece of junk so long as they get to sell you a new BB out of the deal.