Question about CX cable routing

[Lewis Moon]

So...I was looking at the NAHBS photos of CX bikes, and I started to wonder:
Do those little pulleys used to route TT mounted front derailleur cables really get gummed up less than traditionally routed cables?

[nooneline]

Hmm.
Good question.
I'm not entirely sure that it's an issue of getting less gummed up.

CX bikes traditionally do have top-tube-routed cables for a couple reasons - one is to keep the exposed cables a bit further away from possible mud and wet, yes, but the other reason is that with cables running along the downtube, grabbing the downtube to shoulder the bike means you could get your fingers snared in the cables. It's not necessarily a constant problem, but I would find it uncomfortable. So, cables along the top tube (yes, you also grab cable if you lift by the TT, but the contact with the cables is with your palm rather than at your fingers), and the pulley is there so that one can use a bottom-pull, road front derailleur rather than try to find an off-group, mountain-style top-pull derailleur.

[Lewis Moon]

Hmm.
Good question.
I'm not entirely sure that it's an issue of getting less gummed up.

CX bikes traditionally do have top-tube-routed cables for a couple reasons - one is to keep the exposed cables a bit further away from possible mud and wet, yes, but the other reason is that with cables running along the downtube, grabbing the downtube to shoulder the bike means you could get your fingers snared in the cables. It's not necessarily a constant problem, but I would find it uncomfortable. So, cables along the top tube (yes, you also grab cable if you lift by the TT, but the contact with the cables is with your palm rather than at your fingers), and the pulley is there so that one can use a bottom-pull, road front derailleur rather than try to find an off-group, mountain-style top-pull derailleur.

I can understand running the rear on the TT, as there really isn't that much difference, you just have to put the stop on the seat stay rather than on the chain stay. You need a whole new braze on pulley to run a TT routing with a bottom pull derailleur.
I just know that when I ride in wet gunk, the FD ALWAYS gets gummed up, so I figure having another moving part in the linkage in the same area might not be so good. I wonder how much extra drag would result from running the TT route, but having the top seat tube cable stop on the front/right side and the cable running underneath the BB through a teflon tube.
Just thinking out loud.

[oldpotatoe]

So...I was looking at the NAHBS photos of CX bikes, and I started to wonder:
Do those little pulleys used to route TT mounted front derailleur cables really get gummed up less than traditionally routed cables?

Well, No. Some are wee cart bearings but remember that the cable moves very little and even if the pulley isn't turning, it works pretty much the same as a BB guide.

[zennmotion]

This is a preference, there are great hand made bikes using both cable routes, top pull FD is another option that works well. I prefer the cable pulley route because I tend to lift my bike from the downtube rather than "suitcase" from the TT- I'm sometimes lazy or weak or both and I've banged my wheels hard on barriers not lifting the bike high enough. Even though I'm average male height, this is even more of an issue with shorter riders. Grabbing the FD cable on the DT isn't particularly uncomfortable, but I don't like the idea of accidently pulling my FD out of alignment with my hands by pulling on the cable- if it's sticky or frozen it might be a problem when I start pedaling again. But it's just a preference, one of those things cross riders debate endlessly, like moto-style brake lever position or extra top mount levers or BB drop or canti's vs miniVs vs discs, or single ring vs double. It all works but still we argue!

[oldpotatoe]

This is a preference, there are great hand made bikes using both cable routes, top pull FD is another option that works well. I prefer the cable pulley route because I tend to lift my bike from the downtube rather than "suitcase" from the TT- I'm sometimes lazy or weak or both and I've banged my wheels hard on barriers not lifting the bike high enough. Even though I'm average male height, this is even more of an issue with shorter riders. Grabbing the FD cable on the DT isn't particularly uncomfortable, but I don't like the idea of accidently pulling my FD out of alignment with my hands by pulling on the cable- if it's sticky or frozen it might be a problem when I start pedaling again. But it's just a preference, one of those things cross riders debate endlessly, like moto-style brake lever position or extra top mount levers or BB drop or canti's vs miniVs vs discs, or single ring vs double. It all works but still we argue!

well, except there are no, road specific, top pull Fders made.

[zank]

I have found the top pull Shimano CX70 works incredibly well with Shimano levers (of course), Campagnolo Ultrashift and Powershift levers, and any SRAM lever. The one caveat to the SRAM comment is the CX70 and 2012 Red lever combination, which I don't have any first-hand experience with. I'm not saying it won't work well; I just have never set one up myself and can't say for sure.

[gavingould]

there are also bottom pull to top pull adapters... saw these in at least one NAHBS photo, can't recall which bike though.

[zennmotion]

well, except there are no, road specific, top pull Fders made.

Road specific, no. But Lewis was asking about cross bikes in the OP, which I interpret as bikes designed for- you know- cyclocross racing, since he's asking about the pulleys that are designed specifically to address the mud and portaging issues that are unique to cross racing, and of course these use smaller chainrings. I've used a top mount Shimano XT FD with CX-sized chain rings (eg as small as 34, as large as 46t) both Shimano and Campy shifters and it works quite well. I don't know how well it would or would not work with a big ring larger than 46t, so if I were using a cross bike for more road/"all around" riding where I wanted larger rings, you're right, I would not want a top pull FD. But for a cross rig, especially one that's raced in swampy black lagoon or freezing slush conditions? If that's where you race then a top pull FD can't be beat IMO. Thanks for your advice- always appreciated and trusted here!