jaredpc

Hello,

I have begun a project to convert an old Nishiki Sport to a 1x10 gravel bike. I cold set the rear triangle to take the rear wheel I have (135mm hub spacing). I have a 10 speed cassette (11-42t) and a compatible 10 speed derailleur that can mange the range. I now need to figure out which bottom bracket and crankset will work with this set up. The bottom bracket shell is english threaded 70mm, so I figure a standard 68mm bottom bracket should work? However, i am not exactly sure which bottom bracket and then associated crankset will give me the best function and appropriate chainline. I would love some guidance on how to think about this and make sure I get it right. I don't care about weight but would prefer cheaper options.

thanks!

shelbyfv

I'd suggest you pick the crank first, then get whatever bb it requires. The GRX crank is an obvious choice if 40t will work. You might get a little better chainline with GRX than a regular road crank.

Rolla

Just spitballing here, but have you measured the chainline in the rear, now that the spacing has been modified? Maybe start there and then see about finding a 68mm BB and crankset that achieves approximately that number. Might need to use a single spacer on the driveside of the BB and/or play with the inboard/outboard chainring mounting to tweak the chainline at the crank.

Moe Zhoost

Yes, indeed. You can get a pretty good idea of your target chainline by doing some measurements of your rear hub. Matching that to a crank/BB system may then be as easy as going with manufacturer's specs, but I've always had to do some trial and error stuff. For standard square taper BBs, I usually mount a spare BB of known spindle length, measure the chainline offset, and then use that info to determine the final spindle length. External BBs may be easier since it's just a matter of playing with spacers.

With 10-11 speed rears, I can't see that getting chainline exact is a big deal. You'll only be perfect on one of the cogs (or near perfect on 2 of them). More important is that you aligned your rear triangle following cold-setting.

jaredpc

thanks for the replies. I have not checked the chain-line again but tI made sure the frame is pretty well aligned after cold setting. I am not entirely sure how to measure my desired chain-line? I've read sheldon brown's page on chain-line, is there an easier way to get a number for your theoretical chain-line? Looking for cranks before BB is well taken advice.

thanks

Rolla

Rear:
A. With the wheel installed, measure the distance between the inside surfaces of the rear dropouts. Divide in half. You should get a number somewhere around 67.5mm

B. Measure the distance from the center of the middle cog to the inside of the driveside dropout. Subtract this number from the first number. The result is your rear chainline.

Front:
Measure the distance from the center of the seat tube to the chainring. This number should be close to the result you got from above [(1/2 A) - B.] It's often easier to measure from the outer driveside edge of the seat tube to the chainring, and then add half of the seat tube diameter.