cazzooo

I understand one pulls from from top and one bottom, but what difference does it make? Can you use either one just as well?

jeff williams

Depends how your cables are routed?
Bottom pull have a bolt on cable guide under the bb, or routes through the shell.

meb

The traditional bottom pull derailleurs which worked fine for road use had cable run vulnerabilities to dirt thrown up when used on mountain bikes. The mountain bike solution was to redesign the cable runs through less vulnerable locations above.

The top pull fders usually have a cage shaped for a 46-48T large ring so would not shift as well on a 52-53 large ring. Conversly, a bottom pull road bike fder would not shift optimally with a 46-48T big ring. With some bikes (not all) one would need some extra contortions to run the cables to the fder on the opposite side.

khuon

With bottom routed cable-runs, you might want to consider installing a sheath over the housing end to prevent gunk from getting inside. This is on my roadbike and as you can see, even that machine can collect a lot of grime. Of course I haven't cleaned this since fall-riding in the PNW took its toll.

operator

Is that sheath something I can walk in and ask my LBS for?

Retro Grouch 

The big difference has to do with where the cable stops are on your frame. It sounds like rerouting the shift cable would be a simple process but it actually involves semi-major surgery on your bike's frame. There are a few front derailleurs that bat both ways. They are designed such that they will accept a cable pulling from either direction.

I haven't noticed any difference in front derailleur performance. Back in my mountain biking days my bikes had bottom pull front derailleurs and I never had any problems with them. I always just ran the bare cable and never felt the need for a sheath or anything to exclude the crud. I have a very slight preference for BB routed rear shift cables because a seat stay routed cable can allow water to run down and collect in that short little section of cable housing and cause rust. Mostly, I really don't think that it matters.

sydney

Well, I certainly fail to see the point,as there is nnothing but a bare cable from the cable stops on the downtube to to derailer.

jeff williams

I'm pretty sure it's an internal cable routed lower pull derailler. The upper cable is just the end. The sheath fits between the frame route and the derailler.

khuon

Ding! Ding! Ding! You sir, are correct.

jeff williams

Khuon, I'm constantly amazed at the tweaks you have on your bikes.

khuon

Probably... since that's what I did.