Bicycle Mechanics - Crankset and Bottom Bracket help

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nathan-m
01-05-08, 04:22 PM
I'm in the market for a new crankset and am having trouble figuring out the crankset/BB lingo.

I'm looking at either the FSA MegaExo Carbon Compact, or the Shimao FC-R700. Does anyone know what type of BB the Shimano is used with? Or, are cranksets and BBs interchangeable

Ok, maybe i'm totally off here, but i'm just assuming that a crankset comes with a defined BB.

Also, if my current BB is ISIS, can I switch it out for a MegaExo BB?

Basically, i barely know what i'm talking about so any help would be much appreciated.

operator
01-05-08, 04:41 PM
Cranksets and bb's are interchangeable as long as they use the same interface. However usually only one or two bb sizes will give you the correct chainline ofr a conversion.

The crankset usually specifies what BB (length) it needs in order to get some number chainline. So in short, pick out your crankset, then your bb for teh chainline.
Ex Pres
01-05-08, 06:34 PM
Yes, you can swap your ISIS for a X-style.

Don't both of those crankset already come with the spindle attached [to the drive side]? That means that the BB is just the cups, unlike what you are used to.

hbutler
01-06-08, 01:25 PM
Yes, you can swap an ISIS BB for an integrated/external style, such as MegaExo, or Shimano's Hollowtech. Just make sure to get the threading right, either English or Italian. If you get an integrated/external style crankset, you don't have to worry about chainline because the axle is built into the right side of the crank, and is already the correct length. If you stay with a cartridge style BB and crank, like
ISIS or a square taper (don't discount them, there are some nice options for those as well) you will need to get a BB with the proper spindle length to have a proper chainline. It isn't too hard to figure out since most cranks list what length BB they need. Personally, I would go with that Shimano RC700. It shifts better than the FSA due to its better engineered chainrings and I think it looks better, but that is just me.