Hello,

I'm converting my Concord New Yorker (an 80's Japanese knock-offs of the old diamond frame Phillips and Raleighs) from a cottered crankset to cotterless. The bb shell width is 68mm, the threading is 24 tpi. The bike is set up as a single speed with a coaster brake in the rear, with a chainline of about 35mm. My main concern in the conversion is getting the correct spindle length for a decent chainline. I know that the crankset will have some impact on chainline as well, but I want to get in the general ballpark of the correct spindle length. I've been told that you measure the cottered crankset's spindle from the center of one cotter pin indention to the center of the other cotter pin indention, and that should be the square taper axle length to look for:

https://imgur.com/RkPlVnx

(sorry, I can't seem to post pictures here)

But that measures 125mm on my spindle. This was just a single chainring set-up; doesn't a 125mm spindle sound like it would put my chainline waaaaaay out there? I usually hear people recommending spindles around 103-110mm for single chainring set-ups.

Thanks for any help!

Everything is based off the crank you use.

Decide upon your new crankset and then follow the manufacturer's recommendations as regards BB specs. Different cranksets have varying offsets which need different BB spindle lengths so choosing a BB first is putting the cart before the horse.

Maybe a Bike shop can sort out all this stuff given you leave us too much online blind guessing to do anything, remotely..

Do have a 35mm chainline ? , seems short since half of a 68mm bb shell is 34, so I think you dont even know how a chainline is Measured.

Okay, thanks for the input guys. I primarily have experience working on one piece cranks, so I guess I didn't realize how litte standardization there was amongst 3 piece cranks. I kinda thought spindle length was the main driver of chainline here. I have a crankset in mind, but it's off of an old 80's Raleigh MTB (a Sakae SX crankset), so I won't have any manufacturer's specs to go off of. I'll just have to go the old fasion route of trial and error through the LBS .

I know, it does sound a little off (I know 45mm is a typical chainline with a coaster brake), but that's as accurate of a measurement I'm getting with a laced, mounted wheel. 110mm hub (locknut to locknut)/2 = 55mm - 20mm (distance from inside surface of dropout to the middle of the sprocket) = 35mm.

starting point is the Centerline through the bicycle .

60mm of a 120 wide rear drop-out, 34mm of that 68mm wide BB shell , 50mm of the 100mm wide fork tip spread. as if to cut the bike in half right down the middle .


so as is original parts how far is the chainring from the centerline .. It needs replicating with the New (totally Unknown combination of) parts..

Nothing I can say sight unseen Hence the go to a bike shop suggestion.. Good Luck .. It may not be as Cheap as you Desire..

At least square taper cranks as a Type offer a variety of BB spindle length choices .

Oh yeah, I know it'll end up costing me a bit. In fact, it'll end up running me a lot more than I paid for the entire bike ($25), but it's one of those bikes I have a weird sentimental attachment to, so it's worth throwing the money into it .