Chainline Question
 

Hey everyone. I am building up a Nashbar cyclocross frame and I purchased this crank to go with it. http://cgi.ebay.com/NEW-SHIMANO-OCTA...item4cf3880841

The tech docs suggest a 121mm Octalink BB for a 47.5mm chainline. I was going to throw in a 118 for a 46mm chainline. The crank would be used with a 105 triple front derailleur and 135mm rear hub spacing. Would 46mm work? I can't do any real trial and error stuff because I am in Korea and am buying the bottom bracket online. Thanks!

Are you aware that there were two Octalink interfaces, V-1 and V-2? V-1 was used with road cranks (105, Ultegra, Dura Ace) and XTR MTB cranks. V-2 was uses with the other MTB cranks. If the recommended spindle was 121 mm it has to be a V-2 since, AFAIK, V-1 only came in 109 mm (double) and 118 mm (triple) lengths. Be sure the crank is matched to the correct Octalink type.

I am totally aware of both interfaces. The crank I bought was one of their "non series" components. The tech docs say to use a BB-ES25 which is Octalink v2. I can snag one from JensonUSA for 16 bucks. My main concern right now is the 46mm chainline I will be getting with using a shorter spindle, the 45mm recommended for the FD, and the 135mm rear spacing of the frame.

I wouldn't be concerned about the slightly shorter chainline but be sure the chainrings will all clear the chainstays if the crank is closer than the recommended spindle will place it. That would be my primary concern.

That is a definite concern of mine. I have a compact double that I bought and need to get rid of because it wouldn't clear the chainstays. I am assuming that a touring triple crank would be designed to accommodate frames with wider chainstays. If 3mm of overall spindle length determines whether or not the crank is usable with my frame then it was probably iffy to begin with. I just hate not being able to head to a bike shop and buy something, try it, and return it if it doesn't work. Living in Korea is for the birds.

THe deciding factor on chainline should be the hub. Correct chainline means getting the center of your crankset lined up perfectly with the center of the cassette. If you have 135mm rear spacing, I would bet the 47.5mm chainline is better to get the gears lined up.

Generic alignment , on a triple. : middle chainring in plane with middle cog on the rear cassette.
shop locally? Seoul has bike shops , no Doubt.
Go Off Base?

I agree that the BB to get to 47.5mm chain line is ideal given the OP has a 135mm rear hub. http://sheldonbrown.com/chainline.html#standards

I haven't heard of anyone having trouble getting a road triple FD to work with a 47.5mm chain line. I imagine there is plenty of throw available. Can anyone verify this?

Will a 47.5mm chainline shift correctly with road front brifters?

As long as you have a road FD that can swing out far enough.

Any experiences with a 105 triple?

The nearest shop is 10 miles away and I actually bought my 7.3FX from him. I came back a week later and it looks like the owner's repair policy is as follows: "If it doesn't fit, bend it or use a mallet until it does." I saw him do it firsthand to cranks and derailleurs. I think I'll pass and do it myself. Also the language barrier was pretty bad. :P