Question about BB length and cranks...
 

Are there any riding dis/advantages involving BB length and crank spacing?

My BB runs 68x118 and there looks to be space to get a shorter BB so I can bring my cranks in a bit.

Good idea? Bad idea? Preferential?


Also, any thoughts regarding chainring positioning being outboard or inboard of the crank tabs or is that simply an aesthetic call?

The goal is to have your chainring and cog line up i.e. be the same distance from the centerline of the bike.

Read this: http://www.sheldonbrown.com/gloss_ch.html#chainline

Running the chainring on the outside position will allow for a shorter spindle and a narrower Q-factor (distance width-wise from one crank arm to another), which people say provides more powerful pedalling.

Chainring position is all aesthetics so long as it's not a track crank with no inner tabs. In some rare cases the inner tabs might not clear the stays with the ring in the outer position, but I wouldn't worry about it.

118 is a looong bottom bracket, though some old road doubles give you a 42mm chainline on the inside position with this BB length. You can definitely come in, just remember that you need to go shorter by twice as much as you want to move the chainring. Also remember that not all BB's are symmetrical, 110's are the same as 107's on the drive side, I forget what other issues there are but someone else will chime in. A shorter BB will give you less Q factor (the distance between the pedals), though probably not enough to worry about unless you're running clipless and have bad knees. It will also help with pedal clearance a little, so pedal strike will be less likely.

Many thanks for the feedback.