ineedalabotomy

Hi,
Re: Trek7300fx Hybrid (2006)
I wondered if someone can help ? I really need to replace the old Shimano Nexave triple ring 170mm cranks/ 48/38/28 with a suitable equivalent and possibly change the old VP-BC82 .. 24T..73x120mm BB whilst I'm at it, although it is holding up well atm. I have already replaced the cassette for > SRAM PG830 8 Speed 11/32 and the chain KMC x8.. Any recommendations gratefully received.

Tia

hokiefyd 

Cranksets usually have a bottom bracket spindle length specification, so you are sure to get the correct length bottom bracket. For example, the Shimano FC-TX801 crankset recommends a 123mm bottom bracket spindle to achieve a 50mm chainline.

I would measure your existing chainline (the lateral distance from the middle ring to the center of the seat tube) and then adjust from there. For example, if your current chainline is 50mm, then you go right with the 123mm spindle (if you bought that FC-TX801 crankset). If your existing chainline differs from 50mm, then you could add or subtract double that difference for the spindle. For example, if you have and want to maintain a 48mm chainline with that FC-TX801 crankset, then you'd need a bottom bracket spindle about 4mm shorter than spec, or 119mm. If you can't find a 119mm, a 118mm or 120mm would probably work.

Some of this can be a little bit of trial and error. When installing the parts, watch to ensure your chain rings won't scrape the chainstay of the frame, etc.

ineedalabotomy

Thanks for your reply & apologies for the late response. Some useful info and food for thought. Will have a play around. 👍