Hi there, I've got an older frame with two holes in the top tube for an internally routed brake cable. When I bought the bike (second-hand) it wasn't being used, they simply had the brake cable in a normal exterior housing running alongside the top tube. What are the pros and cons of using the internal routing vs exterior? I'm redoing my cables so considering both options.

Also, if I use the internal routing, do I need a narrow housing within the hole, or can you just thread the cable in bare?

Thanks for any advice.