FSA RPM cartridge square taper bottom bracket

[johnjohn]

Greetings,hope this thread is in correct section,never sent one before.
I have a Shimano M151 28/38/48 chainset attached to a FSA RPM cartridge. Can I change the chainset for any other square taper FSA or Shimano chainset.
The reason I am thinking of this is that with my 11-28 8 speed cassette I have high gears I never use on my Giant hybrid. Never use the 11 or even the 12 sprocket. I need to keep the low gearing, it's hilly in North Lancashire. Thanks, Johnjohn.

 

[rusty bearing]

You can but they are becoming far and few between, and mostly 9 speed so narrower chain. Different chain-sets also might have a different spec for the BB dimensions which gives the correct chainline, what you have runs on a 122mm spindle so you need to match that up or its a new BB as well. Why not think about putting a bigger cassette on the back ? Something like an 11-32?

 

[PpPete]

What rb says is true, but I cant see that another Shimano MTB chainset (i.e. one with fewer teeth) is going to change the chainline from what you have now. If you were changing to a road chainset it might be an issue, but you should be safe IMO. If I'm wrong - the cost of a new square taper BB is not huge compared with that of a new chainset.

 

[johnjohn]

What rb says is true, but I cant see that another Shimano MTB chainset (i.e. one with fewer teeth) is going to change the chainline from what you have now. If you were changing to a road chainset it might be an issue, but you should be safe IMO. If I'm wrong - the cost of a new square taper BB is not huge compared with that of a new chainset.

Thanks, the basic idea was to change from 48-38-28 to say 42-34-24 or 42-32-22 which would give me closer mid range gears which I use a lot,remove the totally unused high end ie11-48 (I'm 60 odd yr recrational cyclist) whilst giving me the low end I need.
Ideally I would like a 14-28 cassette and not change the chainset but the days of custom cassettes with individual sprockets have disappeared in the 30yrs since my first cycling life!

 

[PpPete]

Not impossible to create a custom cassette. A couple of years ago when I converted my then best bike (an 80's steel tourer) to triple 9 speed I found the standard ratios were too high for me, or the gaps in the MTB cassettes too wide. In the end I bought 2 different low cost cassettes (about £15/ea), ground off the rivet heads that hold the block element together, and mixed up the sprockets to give me a 12-30 with acceptable gaps and which still worked with a "road" rear mech. This was significantly cheaper than any of the bespoke options like the Harris Cyclery one for similar ratios.
Since then I discovered I preferred Campag Ergos to Shimano STIs and so my new bike is all Campag - which gives me access to their 13/29 cassette ( not a million miles from your ideal 14-28)

 

[RecordAceFromNew]

Not impossible to create a custom cassette. A couple of years ago when I converted my then best bike (an 80's steel tourer) to triple 9 speed I found the standard ratios were too high for me, or the gaps in the MTB cassettes too wide. In the end I bought 2 different low cost cassettes (about £15/ea), ground off the rivet heads that hold the block element together, and mixed up the sprockets to give me a 12-30 with acceptable gaps and which still worked with a "road" rear mech. This was significantly cheaper than any of the bespoke options like the Harris Cyclery one for similar ratios.

+1. I regularly mix and match sprockets from different cassettes.

To answer the original question I think the chance of hitting the right chainline by purchasing ANY chainset without changing the square tapered bb is not great. Many Shimano modern ones' (and older ones here) requirements are here.