chain line.... again!?

[Wilson jr]

Hi guys. I'm new to this bike building malarkey. I'm building up a bike with some new parts and some parts that I "inherited". Basically I would like some advice on bottom bracket spindle/axle length. At the moment I have a 122.5 mm axle in and with a carefull bit of measuring have found my chain line to be 7mm too far out on the crank end. Now am I right in saying for it being 7mm out I'd need a 14mm shorter spindle/ axle length? (7mm each side?) Any help would be appreciated. Cheers.

 

[Yellow Saddle]

Yes

 

[midlife]

Depends if it's an asymmetric axle...

 

[Wilson jr]

Thank you yellow saddle. The chain line is the only part of build that has concerned me. The rest has been very enjoyable and almost therapeutic. Now ordering smaller bb. Fingers crossed.

 

[Wilson jr]

Shimano un55 fitted at the moment with 122.5mm axle length.

 

[Yellow Saddle]

Thank you yellow saddle. The chain line is the only part of build that has concerned me. The rest has been very enjoyable and almost therapeutic. Now ordering smaller bb. Fingers crossed.

Just confirm with your measurements that you can afford to lose 7mm on the left side.

 

[midlife]

Just confirm with your measurements that you can afford to lose 7mm on the left side.

Yup, Losing 7mm on the non-drive side might have the crank banging against the BB ...

 

[Wilson jr]

I'm pretry sure there is room but as you suggest I will double check. I did measure crank side and have around 12mm to play with before the chain ring hits the chainstays.

 

[Wilson jr]

I had the 122.5mm bb in a box of bits given to me and thought it would be a place to start. Am happy as I have a reference measurement to work with to get chain line as straight as possible before spending money on nearly the right part.

 

[Wilson jr]

So, I just had a measure up. I have 20mm before the crank arms hit the chain stays. 13mm before the chain ring hits the chainstay. So i am going to try a smaller axle length on the bottom bracket. That will hopefully give me a straight (as possible) chain line. I'll keep you posted. Thanks for your advice.

 

[Wilson jr]

Just checked sizes available, closest I can seem to find is 110 mm. My measurements say ideally I'd need 108.5mm. So my next question.... would a 110 mm bottom bracket with a 1mm spacer at frewheel give me a straight enough chain line? it would leave me in theory .5mm out. Sorry for the schoolboy questions.

 

[Yellow Saddle]

Just checked sizes available, closest I can seem to find is 110 mm. My measurements say ideally I'd need 108.5mm. So my next question.... would a 110 mm bottom bracket with a 1mm spacer at frewheel give me a straight enough chain line? it would leave me in theory .5mm out. Sorry for the schoolboy questions.

Yes, that would be fine.

 

[Wilson jr]

Thank you. Just ordered bottom bracket and spacer set that should allow a perfectly straight chain line. Will let you know how I get on.

 

[midlife]

Thank you. Just ordered bottom bracket and spacer set that should allow a perfectly straight chain line. Will let you know how I get on.

Measure twice and buy once lol

 

[Wilson jr]

Just a quick update on the chainline issues I was having. Glad to say it's sorted. Thanks guys for clearing things up.