Bike Forums - View Single Post - Need help with chainline/bottom bracket calculations

07-03-22, 04:53 PM

#6

SoSmellyAir

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Quote:

Originally Posted by alexk_il

I have new rebranded Sugino 42/26t cranks. My bike has BB30, I am planning to install FSA BB30 to standard threaded adapter. I will need a 68mm square JIS BB for these cranks, these come in different lengths, so I am in position to just chose the right size.

Here is my math.

My bike has chainline of 44mm, with a new cassette I will need 44-1.7=~42mm.

According to the shop, my new cranks have 43.5mm chainline with 68x116mm bottom bracket. A standard Shimano UN300 can be bought in 113mm. This should bring the chainline down to required 42mm.

Did I get this right?

Yes, your math checks out.

I highly recommend you spend $15 more for a Made in Japan Tange Seiki LN-3922 bottom bracket:

Tange LN-3922 Bottom Bracket | (benscycle.com)

Tange LN-3922 Square Taper Bottom Bracket – The Bikesmiths

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