Alright. I understand what chainline is, but I’m a little unclear as to what factors play in. I read through Sheldon’s page and now I’m more confused.
SO…
It is the distance measured from the center of the chain, to the center of the seat tube? If I have a crankset on one bike and I want to calculate the BB length I should use on another frameset, can I do this?
Center of ST to center of chainring.
The other frameset should accept the same length BB per crankset regardless of frame. Frames do not determine chainline - that’s all up to the rear hub chainline/cog brand, and BB length/taper/cranks.
Can’t remember if whether a frame has an Italian vs. English BB shell makes a difference in what length BB you need though.
It’ll be english to english anyways.
So basically, if I measure my chainline on my current frame and know the length of the bb spindle, that will give me an idea of spindle length I’d need on the new frame?
Yes as long as your chainline is on.
A quick and easy method I use to see if chainline is on without measuring (since the difference of a couple mm’s in measurement is pretty easy to attribute to human error) is put the bike on a bike stand, give the pedals a good spin, and when everything comes to a complete stop, closely eye how the chain engages on the chainring teeth and cog teeth. If everything is good, it should be perfectly or near perfectly centered. If it’s off to one side or another, you got problems.
[quote=EivlEvo]Alright. I understand what chainline is, but I’m a little unclear as to what factors play in. I read through Sheldon’s page and now I’m more confused.
SO…
It is the distance measured from the center of the chain, to the center of the seat tube? If I have a crankset on one bike and I want to calculate the BB length I should use on another frameset, can I do this?[/quote]
are you using the same crankset on the new frame? if so, it should say the bb spindle length on the bb. what crankset anyway?
Yeah I am, but a new BB. Its a Shimano 600 set that I’m obv running as a single. But it also wasn’t running with the stock 600 BB (which is on my gf’s bike) (this set had a bent chainring so I swapped it to 1/8".
cross chain as much as possible
pretty sure you need a 107mm JIS spindle for those cranks.
shit… thanks for reminding me about JIS vs. ISO… TOTALLY slipped my mind.
i’m only going from memory and never measured the chainline when i had those cranks on, but the chain was fucking silent when it was clean and it looked very straight…
I’ve been pretty much planning to get a 107 after doing some measurements. But I was about to order and I wasn’t even THINKING JIS or ISO.
It looks about right, and if its noisy I’ll just have to kill people by walking up behind them.