BBK confusion.

[Gillstay]

Hi. I am converting my bike to a 3 x 10 setup and think Tiagra bits will do it nicely. Flat bars, getting older so need to gears for hills.

Looking at bottom brackets I can see a BB-RS501 and an RS500 is one for the double and the other for the triple as it does not say clearly as far as I can discern.

All the rest looks quite clear but if anyone has done this recently and has any advice I would be glad to hear it. Thanks.

 

[Ajax Bay]

Assuming Tiagra chainset FC-4703, either BB would do you (assume 68mm and threaded BB shell).
Edit: To get the chainline 'right' - the spacer (numbered '11') is used.
https://si.shimano.com/en/pdfs/ev/FC-4703-3934/EV-FC-4703-3934B.pdf

 

[Gillstay]

Assuming Tiagra chainset FC-4703, either BB would do you (assume 68mm and threaded BB shell).
The crankset gets the chainline 'right'.
https://si.shimano.com/en/pdfs/ev/FC-4703-3934/EV-FC-4703-3934B.pdf

Oh, thats a handy link and your assumptions are correct. I should have been clearer. Thank you.

 

[Gillstay]

Why would they have two BB's so very similar though ?