hey all,

so i'm working on upcycling an old mtb. i had replaced the hub quite awhile back and thought i put a 123 mm bb in last time. i guess it was a little longer, measured about a 125 (i can't read it on the cartridge anymore). so i also replaced the cranks and chainrings, and dropped down a few teeth. the inner ring does not come close to the chain stay now (whereas with the old crank i had like 2 mm clearance or less). the new bb axle is 123 mm, and i'm wondering if you guys think it will cause any problems. just asking what the main difference is, and if it's ok to shorten that a little. want to ask before i change out the rear wheel and put on a new chain just to find i have some unforseen problem.

it looks like the chain line will be ok, so what's the big deal with having specific axle lengths?? just better for these super tight clearance modern designs?

thanks for any opinions and advice...

You have to analyze what the purpose of a "correct" chainline is-
If you have a triple & odd number of cogs, the chain should be parallel to the centerline of the bike when on the middle ring & cog.
A double and/or even number of cogs will change this slightly.

I tend to use the middle ring & outer cogs, so I run a slightly longer spindle to keep the chain running "more straight" on the cogs I use the most.

there is a mating of crank design and BB spindle length some cranks facilitate a shorter spindle

others necessitate the spindle come out to meet the crank arm...

chain line is a line parallel to the bike centerline.. aligning centers of gear cluster and crankset ..

a double & even number of speeds on rear cluster, it is the space between the central 2..


Will 2 mm matter to you?








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