Hi, I just ordered a frame of chainreaction and the sizing info is 68mm for the Bottom Brackett, I was thinking of getting some 'Shimano LX Cranks HollowTech II & BB M580' http://www.chainreactioncycles.com/Models.aspx?ModelID=7251 they are going for a bargain £70 on here.

My question is what is the sizing info related to? You can get 170mm or 175mm? Is this the crank arm length?

When you look at most bottom bracketts the length is also quoted, eg 68-110mm or 68-113mm. How do I know if these will be suitable to fit my frame? The frame is this one, http://www.chainreactioncycles.com/Models.aspx?ModelID=6073

Thanks for any help

You don't need to buy an additional BB with the Hollowtech II cranks as it comes with the chainset. It fits both 68 and 73mm frames. Yes the 170 and 175 are crank length. 175 is normal on an MTB.