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My bike is this:

https://www.santafixie.co.uk/derail-black-fixed-bike.html

The BB measurements on the link are CH55 BSA 68/107.

I know literally bare minimum about bottom brackets and crank sets. I wanted to get this Miche Primato advanced track crank set and I need some ideas of what bottom bracket I could get that would work with this and my bike. (my bottom bracket currently has play in it so I need a new one anyway).

Or if anyone could check my current specs and recommend a compatible BB and crank set (preferably 48t) that is good. I know there are other factors like chain line width but as I've given the BB length I'm thinking a same length new one would be the same chain line width?

Cheers.

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    We don't really give product recommendations here, but it would help if we knew why are replacing the crankset. – ojs Mar 29 at 19:52
  • The crank set I currently have is generic factory made, I guess i'm just trying to upgrade the parts of the bike that are actually worth upgrading, like wheels and crank set. – Luke Russell Mar 29 at 22:29
  • Upgrading a bike part by part is going to be far more expensive than buying a better bike, and you have to consider parts compatibility at each step. Anyway, with that bike I'd start upgrading from frame and wheels, unless there is a specific problem with the cranks. – ojs Mar 30 at 6:08
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Like most bicycle components cartridge bottom brackets are highly standardized. Almost all bikes with threaded bottom bracket shells are ISO standard: 1.37inch x 24 threads per inch, drive side is left hand threaded. The ISO standard is also known as 'English' or 'BSA'. Obviously this is what your frame has.

There are two other parameters you need to know. Frame bottom bracket shell width and axle length.

Standard widths are 68mm and 73mm. The shell width is very easy to measure. Some cartridges will fit both a 73mm shell and a 68mm one with two 2.5mm spacers.

Different models of cranks require a different length axle to get the same chainline. This is because the square taper in the crank arms can be in a different position along the axle axis (closer to or further away from the center of the frame. In general you can't put a different crank on a given BB and definitely expect the chainline to come out right.

What you need to do is know or measure what you chainline is, make sure you are buying a crank that gives you the correct chainline, get the correct bottom bracket axle length for the crank, and bottom bracket shell width of your frame.

If you are buying Shimano they make this very easy as they publish extensive specifications and compatibility. With other manufacturers it can be more difficult. I found some data for the Miche crank here, and I note that in actual fact it calls for a BB axle length of 107mm for a chainline of 42.5mm (which I assume is the standard for track bikes).

Another example, the manual for the FSA Vero Pro specifies a 110.5mm axle for chainline of 44mm.

You can of course modify the chainline of a square taper crank by getting a BB with an axle greater or less than what is specified (remember that to get 1mm of chainline difference you need 2mm difference in axle length).

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  • I have measured my chainline and it is around 45mm? So I need a BSA 68/107 BB and a crankset with a 45mm chainline? – Luke Russell Mar 29 at 22:53
  • 45mm seems a bit wide, chainline is a little tricky to measure, I'd check it. Also try measuring rear chainline as you have a single speed and want the front and rear sprockets to align. Also look at what chainline various track cranks offer i.e. the Miche is 42.5. Read this for info on chainline sheldonbrown.com/chainline.html – Argenti Apparatus Mar 30 at 1:01
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    Re So I need a BSA 68/107 BB and a crankset with a 45mm chainline. No. You need a crank with the required chainline (45, or 42 whatever it turns out to be), and the BB axle length that the crank documentation specifies. – Argenti Apparatus Mar 30 at 1:04
  • The Vero pro looks like it's meant for 1x derailleur setups, not singlespeed. This explains the chainline. – ojs Mar 30 at 9:17
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    @ojs, just using it as another example – Argenti Apparatus Mar 30 at 11:20
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BSA 68 is the bottom bracket shell type. BSA determines the threads an shell length, so this needs to match the frame, so it should be the same as old BB. 107 is axle length. This is determined by the crankset, so you need to find the specs for the crankset you want and take the number there. Track bikes have standard chainline, so unless you want to misalign the chainring and cog, the length from crankset's specs is the correct one.

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