I've upgraded drivetrain bits for for a few folk and the ones I've seen have all followed roadie - 68mm bb shell with a 43mm chainline and 130mm rear OLD. One guy had bought an XT triple drive train for some reason but it installed and road fine - just had to mess about with the spacers - I put them all on the none drive side bb rather than 2 and 1 as supposed to be and the chainline was near as dammit - about 1mm out so not an issue. Couldn't guarantee that they are all like that though - check the specs of the one you want to buy before parting with cash, just to be sure. Can't see any reason why they would follow MTB specs to be honest they need big chain rings because of the small wheel size so I would have thought that the narrower the rear dropouts the better for that.
Thanks, thats interesting to hear. Seeing that you put no spacer on the drive side, that means you brought the crank in about 5mm. (spacer is 2.5mm i believe) that would bring the chainline to about 45mm.
I guess it depends on the spec of the rear hub/fork OLD of the small wheeled bike. The reason I raised this question is because I've come across 3 'road-like' double cranks and attempted to fit them on an old steel bike (126 OLD) with narrow BB's (110 or less) and they never quite gave me the chainline I need. its likely that these low end cranks (except for 1 non series shimano) all came from MV bikes.
These suspected MV cranks gave me chainlines of around 55mm of which road FD's were not able to reach far out enough. In one trial, I had to resort to a MTB FD for the extra reach to guide the chain into the outer chainring
I've currently got another 126OLD frame with another cheap crank / 110 bb and again it's not fitting. Thus am suspecting that my 126 OLD frame does not mate well with modern day road cranks. Perhaps its the thinner steel tubes vs oversized Alumium/carbon frames.
Are you talking about square taper / octalink style cranks / BB's? If so you need to work out what spindle length BB cartridge you need based on the chainline spec of the frame and crank or you could shove a wheel and casette in and use a straight edge to measure the chainline. The problem is going to be getting hold of an odd size cartridge these days.
Or you could always get out the bastard file and push out the high limit stop on the 43mm roadie FD
I was talking square taper. I've given up on octalink! difficult to find and got to watch our for Octalink I or II. Anyway, the question for the chain line was a theoretical interest based on the situations I faced. I've just ordered in some Hollowtech II cranks and will take it from there.
and you know.. i never thought about filing down the high stop limit! Geez thats brilliant!!