Trek Earl Chainring change
 

I would like to change the chainring on my Trek Earl to a 46 or possibly a 48 and change the crank also. Anybody know what type and size (square, splined) of BB is installed at the factory? I was looking at the Omnium or the Sugino 75 cranks. There isn't much in the way of specifics on Trek's website or in the manual.

Considering your two choices, it doesn't matter what length or type spindle your current BB has.

If you get Omniums, they don't use a traditional spindle and include a GXP BB specific to that crank. If you choose Sugino 75s you will need to use a BB having a 109mm ISO spindle, which I am 100% certain your stock BB does not have.