BB Axle Size

Hi all,

Looking to install a new bottom bracket into a shell of 73mm.

Wondering what axle length would be required to give sufficient clearance.

I’m thinking between 113mm and 118mm… does this sound about correct?

Will be running square taper 170mm cranks.

Thanks in advance.

Axle length is set by chain line not by clearance. Get the chain line right and the clearance should follow unless you’ve got a very odd mix of components. Besides, 73 is only 2.5 mm greater per side than 68 and I’ve always seen more than 2.5 mm clearance, even on my bike with a 103 mm axle.

Cool, thanks for that MiG

Since its an English Threaded MTB BB shell, I’d use the 118 for a 50mm chainline.

so there are two square taper types - JIS (Japanese) and (ISO) European. Make sure you use the one which is compatible with your cranks.

118mm seems quite long (?) I use a 110 with my sugino RD cranks and miche primato hub, for perfect chainline (and the sprocket’s positioned fairly wide on the hub). I would have thought that a 118 was designed for a triple crankset and would push the crank arms out too far for the chainring to be aligned with the track sprocket (unless it is mounted on the inside of the crankarms - which is fugly). But it all depends on your cranks, perhaps you have a friendly LBS that can help you get the right one since you’re fitting it for the first time - which I would have thought was probably just a process of elimination. Good luck.