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Top-tube Routing the RD Cable

1548 Views 3 Replies 3 Participants Last post by  FBinNY
I have an '07 Specialized Hardrock. The standard cable routing is via the down tube, and under the bottom bracket, which I think is stupid. I just had to chuck my cable and housings anyway, so I'm planning to do top-tube routing instead. This is just for the rear derailleur - I haven't touched the front derailleur, and I think I'll probably just leave it routed as is if/when I have to replace it.

I'm not totally sure how I want to do it. I switched to hydraulic disc brakes, so there are cable stops available on the top tube, on the left. The bend doesn't look too bad if I route the derailleur cable from the aft cable stop, around the left side of the part of the seat tube that projects above the top tube, and then down the top of the chain stay. It's also an aesthetic match for the brake cable routing. However, the cable housing has to cross right over the brake line if I do that, and it seems like I'm introducing an extra bend in the rear part of the housing. I'm also not too happy with how tight the bend in the derailleur cable has to get up by the handlebars if I crank my handlebars hard over to the left. I don't know if it would cause a problem in normal riding, though.

I'm also thinking it might make more sense to ignore the cable stops and just run a full length housing. If I did that, I could zip-tie the housing to the top tube further back, and give it a little more breathing room up by the head tube. I have fairly narrow, low handlebars, so there's not a ton of distance to travel. I still have to get from the left side of the bike to the right side of the bike using that routing, although I imagine I could get a pretty straight run if I cross under the top tube on my way to the chainstay, and then follow the chainstay however is easiest.

I could just route the rear derailleur cable to the right of the head tube, but I don't want to introduce that much bend. I had it routed to the left on its way to its cable stop and used crossover routing under the down tube in the previous configuration, and I think going to the left of the head tube makes the bend a lot mellower.

So I'm curious as to how other people with top tube routing have done it, especially on bikes designed with down tube routing.
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As long as you stay to the left of the head tube, I don't know why any of your options wouldn't work well. Since you have empty cable stops on the tt, I would probably use them and stay on the left side of the seat tube. In the end, no one else is likely to notice how you route it.
I talked it over with my mechanic, and just did downtube routing again. He said that on bikes with a very sloping top tube, the housings actually collect even more debris than with the downtube routing. Hopefully between a nicer rear derailleur, new housings (that I was a little anal about) and knowing that the bb shell is something I have to keep an eye on, I'll get better performance than I was. Certainly at the moment, the bike is shifting better than it ever has.
Top tube routing for RD cables was popular for a short while. The assumption would be that it would eliminate the crud that gets onto the wire at the BB.

The problem is that the seatstay fulcrum (cable stop) is open to the top, so that gravity would help mud thrown onto the seatstay dribble down into the rear housing loop.

If you use full length housing, toptube/seatstay routing may be better because of less bend in the rear loop, but otherwise the chainstay is a better place for the rear fulcrum.
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