What's the significance of "Inside" vs "Outside" caliper hose connection?

Question

When Shimano rolled over from the "x000" series mtb brakes (e.g. 6000, 7000, 8000) to the x100 series, one thing that changed is where the hose connects to the caliper. Before, it was on the out (left) side. Now it is on the "in" (right) side. What does this do and which routing should I prefer?

Seems like maybe the inside routing might be for bikes that run hose within the chainstay? (ugh, pain to service pivots), but does it also have advantages for those running hose external to the stay but on the inner side as many do? I notice inner side of stay routing to outside caliper connection often puts a wear groove in seatstay and hose-- would inside caliper routing be an improvement despite the hose being closer to moving spokes and debris?

Answer 1

I think the main purpose is to help with the hose routing. Disc brake calipers are generally outside of the chainstay, so having the hose on the inside of the caliper reduces the angle formed by the caliper-chainstay transition. While this does put the hose closer to the spokes, more importantly, it protects the hose from external impact. Disregarding a few mm of wheel flex, the spokes are essentially stationary relative to the hose, so there's no risk there if adequate clearance exists. On the other hand, all sorts of funny business can happen that may result in the outside of the bike being hit, which is where the old routing was.

Another possible benefit is having the hose and bleed nipple on the same side of the caliper. Older calipers often had them on different sides, meaning there was a less direct path for air bubbles to escape via. Now, I don't know whether the change in hose routing directly allowed for this or if it was due to some other engineering factors, but it's certainly a nice benefit.

I will admit that the new routing style makes it somewhat more difficult to access the banjo bolt for hose repositioning, but that's a minor concern considering you really only need to do that once in the life of the brake installation.