This was my first attempt at internal cable routing and it went ok. I pretty much copied Little Fish Cycles’ blog post about this so it’s nothing huge to share. I bought the internal routing ‘kit’ is sold by Nova Cycles and it includes a brass internal tube that is 7mm outside diameter and 500mm in length. It’s just for the cable to pass through – unlike how some other builders do internal routing by using stainless steel tubes (1/4″ x 0.016″) or 9/32 x 0.014″ brass tubing, which have a large enough inner diameter to pass the entire cable housing through (see this link for an example). Both are viable options for internal routing, but both are both heavier and way more complicated to fabricate than using external cable stops. The internal routing I’m using for this cross bike is not that much heavier than normal routing (weight of brass tube isn’t that much) but I am not sure I’ll use this method any longer and instead opt for the internal stainless sleeves so to run full length cable housing. It looks cleaner (to me) and ensures that no water will ever get in to muck up the cable, whereas with the brass tube there is a possibility that water or dirt can still get in and make braking less smooth. If it does get gunked up, at least it’s easy to clean with spraying some some WD40 in there and blowing it out with an air compressor! I didn’t have any stainless tubing lying around and did have the Nova system in house so there you go. It does look pretty cool when done no matter how much a pain it was to drill, file, fit, and braze in there! The braze-ons are VERY thin so they’re easy to overheat with the torch.
The main reason not to do internal routing is that external cables are though easier to swap & maintain/clean. But you could run Gore cables for protection in wet conditions, or you can just run plastic sheaths that slide over the cables between cable stops on the top tube. For shifters, it definitely needs to be friction free so having the ability to at least run one stretch without housing (top tube) would make them easy to clean. The lower section from the top tube down to the rear derailleur could be enclosed and protected from the elements in housing. But externally routed would be so easy compared to fishing/bending/brazing an internal tube down the seat-stays or chainstays from the top tube! It’s all possible, but it’s definitely more time and money to do internal cables! I estimate that this method takes 1-2 hours depending on how many cables you’re running internally where as external braze-ons take maybe 10 minutes for all of them.