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I feel like I'm missing something and can't figure out what size bottom bracket to buy. I'm planning on building a bike and am picking out all the parts before I buy them. I am planning on buying a Poloandbike CMNDR frame and Sugino Pista Crankset. I was looking on the geometries for the frame and couldn't find a description for the size of the bottom bracket I need. Is this something I would figure out in some other way?

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More than likely it's a 68mm wide English threaded BB shell on the frame. You may just want to wait until you get the frame to verify that. The Tech Specs on page for the crankset actually do say that it's designed for "103mm bottom bracket" and "JIS Square Taper". Those should be all the measurements you need (assuming the frame is 68mm English): 68/103/JIS.

If you want a matching Sugino BB, here's one: https://www.ebay.com/b/Sugino-Square-Taper-JIS-Bicycle-Bottom-Brackets/177805/bn_5810397

  • This seems like a silly question but I can't figure it out: how can I figure out what size crank bolt to buy for these? – TheStrangeQuark Jun 29 '17 at 12:56
  • Many BB units will come with bolts. But if you need to get some, standard for square taper is 8mm diameter. – Noah Sutherland Jun 29 '17 at 14:13
  • Sounds good. And I'll just need a bottom bracket tool and torque wrench for installation? – TheStrangeQuark Jun 29 '17 at 14:29
  • BB tool, yes. I don't think a torque wrench is necessary. You screw it in from the drive side until the flange is firmly against the frame. Then screw in the "cup" on the non-drive side just until it's solid (it's really just a spacer to keep the cartridge aligned properly). Make sure you look at the threads carefully since the two sides thread in opposite of each other. Grease the threads and be VERY careful not to cross-thread when you put it in. It's easy to goof it up. – Noah Sutherland Jun 29 '17 at 19:40
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    The most common cartridge BBs will be compatible with Shimano spline pattern. I recommend the Park BBT-32: parktool.com/product/… There are, of course many exceptions to the compatibility, this is the most common. It's also good to find a way to clamp the tool in place, especially if you are trying to remove a stuck BB. Here's one way to do that: youtube.com/watch?v=2wzA6MsRPJE – Noah Sutherland Jun 30 '17 at 15:58
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One simple solution: Search your bike manufacturer website!

Another solution: Go to authorised shimano dealers and ask for advice!

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    Another: Take the old one to a LBS and they can measure it with calipers and tell you what size you need. – Criggie Jun 23 '17 at 7:02
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    @Criggie - Actually, even with the old BB assembly in hand it's often hard to judge the shaft length and offset, since, on square-taper units, the reference point for the measurement is an arbitrary point along the end of the shaft. – Daniel R Hicks Jun 23 '17 at 12:02

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