Cable Routing in General

[MacB]

I was doing some work on the boys bikes and one of them has both gear cables and the rear brake cable routed along the top of the top tube. This struck me as very practical for fettling, not getting covered in road gunk and for spotting if there are cable issues. I can understand that they may be more likely to get snagged accidentally but couldn't that be sorted by a hard case covering that encompasses all three cables?

Are there mechanical reasons for routing cables under the BB or is it more to do with aesthetics?

 

[Moodyman]

I was thinking of this too recently.

My new Trek hybrid has all 3 cables on the top of the top tube and it's great for keeping them clean and out of harm's way.

I was forever cleaning the cables of my old bike which ran along the downtube.

I think it must be aesthetics.

I've noticed that Trek pay a lot of attention to detail - they were amongst the first first to put the rear disk brake caliper between the chain & seat stay to get round the rack fitting problem.

 

[Landslide]

Under the BB requires less sections of outer. The less sections, the less friction and kinks.
Also, on top-routed bikes, the final section of outer before the rear mech tends to point up on the seatstay, thus facilitating the ingress of water.

 

[MartinC]

This is common on cross bikes and MTB's - to keep the cables away from the mud as far as possible. As the previous poster has pointed out it's not perfect though.